Matthias C. Hoffmann

All Publications

• Element-specific ultrafast lattice dynamics in FePt nanoparticles STRUCTURAL DYNAMICS-US Turenne, D., Vaskivskyi, I., Sokolowski-Tinten, K., Wang, X. J., Reid, A. H., Shen, X., Lin, M., Park, S., Weathersby, S., Kozina, M., Hoffmann, M. C., Wang, J., Sebesta, J., Takahashi, Y. K., Granas, O., Oppeneer, P. M., Durr, H. A. 2024; 11 (6)

  View details for DOI 10.1063/4.0000260

  View details for Web of Science ID 001351080800001

• Element-specific ultrafast lattice dynamics in FePt nanoparticles. Structural dynamics (Melville, N.Y.) Turenne, D., Vaskivskyi, I., Sokolowski-Tinten, K., Wang, X. J., Reid, A. H., Shen, X., Lin, M. F., Park, S., Weathersby, S., Kozina, M., Hoffmann, M. C., Wang, J., Sebesta, J., Takahashi, Y. K., Grånäs, O., Oppeneer, P. M., Dürr, H. A. 2024; 11 (6): 064501

  Abstract

  Light-matter interaction at the nanoscale in magnetic alloys and heterostructures is a topic of intense research in view of potential applications in high-density magnetic recording. While the element-specific dynamics of electron spins is directly accessible to resonant x-ray pulses with femtosecond time structure, the possible element-specific atomic motion remains largely unexplored. We use ultrafast electron diffraction (UED) to probe the temporal evolution of lattice Bragg peaks of FePt nanoparticles embedded in a carbon matrix following excitation by an optical femtosecond laser pulse. The diffraction interference between Fe and Pt sublattices enables us to demonstrate that the Fe mean square vibration amplitudes are significantly larger that those of Pt as expected from their different atomic mass. Both are found to increase as energy is transferred from the laser-excited electrons to the lattice. Contrary to this intuitive behavior, we observe a laser-induced lattice expansion that is larger for Pt than for Fe atoms during the first picosecond after laser excitation. This effect points to the strain-wave driven lattice expansion with the longitudinal acoustic Pt motion dominating that of Fe.

  View details for DOI 10.1063/4.0000260

  View details for PubMedID 39582608

  View details for PubMedCentralID PMC11585363

• Author Correction: Non-equilibrium pathways to emergent polar supertextures. Nature materials Stoica, V. A., Yang, T., Das, S., Cao, Y., Wang, H. H., Kubota, Y., Dai, C., Padma, H., Sato, Y., Mangu, A., Nguyen, Q. L., Zhang, Z., Talreja, D., Zajac, M. E., Walko, D. A., DiChiara, A. D., Owada, S., Miyanishi, K., Tamasaku, K., Sato, T., Glownia, J. M., Esposito, V., Nelson, S., Hoffmann, M. C., Schaller, R. D., Lindenberg, A. M., Martin, L. W., Ramesh, R., Matsuda, I., Zhu, D., Chen, L. Q., Wen, H., Gopalan, V., Freeland, J. W. 2024

  View details for DOI 10.1038/s41563-024-02044-2

  View details for PubMedID 39402217

• Non-equilibrium pathways to emergent polar supertextures. Nature materials Stoica, V. A., Yang, T., Das, S., Cao, Y., Wang, H. H., Kubota, Y., Dai, C., Padma, H., Sato, Y., Mangu, A., Nguyen, Q. L., Zhang, Z., Talreja, D., Zajac, M. E., Walko, D. A., DiChiara, A. D., Owada, S., Miyanishi, K., Tamasaku, K., Sato, T., Glownia, J. M., Esposito, V., Nelson, S., Hoffmann, M. C., Schaller, R. D., Lindenberg, A. M., Martin, L. W., Ramesh, R., Matsuda, I., Zhu, D., Chen, L. Q., Wen, H., Gopalan, V., Freeland, J. W. 2024

  Abstract

  Ultrafast stimuli can stabilize metastable states of matter inaccessible by equilibrium means. Establishing the spatiotemporal link between ultrafast excitation and metastability is crucial to understand these phenomena. Here we utilize single-shot optical pump-X-ray probe measurements to capture snapshots of the emergence of a persistent polar vortex supercrystal in a heterostructure that hosts a fine balance between built-in electrostatic and elastic frustrations by design. By perturbing this balance with photoinduced charges, an initially heterogeneous mixture of polar phase disorders within a few picoseconds, leading to a state composed of disordered ferroelectric and suppressed vortex orders. On the picosecond-nanosecond timescales, transient labyrinthine fluctuations develop, accompanied by the recovery of the vortex order. On longer timescales, these fluctuations are progressively quenched by dynamical strain modulations, which drive the collective emergence of a single vortex supercrystal phase. Our results, corroborated by dynamical phase-field modelling, reveal non-equilibrium pathways following the ultrafast excitation of designer systems to persistent metastability.

  View details for DOI 10.1038/s41563-024-01981-2

  View details for PubMedID 39317816

  View details for PubMedCentralID 8024274

• Dynamical decoding of the competition between charge density waves in a kagome superconductor. Nature communications Ning, H., Oh, K. H., Su, Y., von Hoegen, A., Porter, Z., Capa Salinas, A., Nguyen, Q. L., Chollet, M., Sato, T., Esposito, V., Hoffmann, M. C., White, A., Melendrez, C., Zhu, D., Wilson, S. D., Gedik, N. 2024; 15 (1): 7286

  Abstract

  The kagome superconductor CsV3Sb5 hosts a variety of charge density wave (CDW) phases, which play a fundamental role in the formation of other exotic electronic instabilities. However, identifying the precise structure of these CDW phases and their intricate relationships remain the subject of intense debate, due to the lack of static probes that can distinguish the CDW phases with identical spatial periodicity. Here, we unveil the out-of-equilibrium competition between two coexisting 2 × 2 × 2 CDWs in CsV3Sb5 harnessing time-resolved X-ray diffraction. By analyzing the light-induced changes in the intensity of CDW superlattice peaks, we demonstrate the presence of both phases, each displaying a significantly different amount of melting upon excitation. The anomalous light-induced sharpening of peak width further shows that the phase that is more resistant to photo-excitation exhibits an increase in domain size at the expense of the other, thereby showcasing a hallmark of phase competition. Our results not only shed light on the interplay between the multiple CDW phases in CsV3Sb5, but also establish a non-equilibrium framework for comprehending complex phase relationships that are challenging to disentangle using static techniques.

  View details for DOI 10.1038/s41467-024-51485-5

  View details for PubMedID 39179535

  View details for PubMedCentralID 9950456

• Terawatt-scale attosecond X-ray pulses from a cascaded superradiant free-electron laser NATURE PHOTONICS Franz, P., Li, S., Driver, T., Robles, R. R., Cesar, D., Isele, E., Guo, Z., Wang, J., Duris, J. P., Larsen, K., Glownia, J. M., Cheng, X., Hoffmann, M. C., Li, X., Lin, M., Kamalov, A., Obaid, R., Summers, A., Sudar, N., Thierstein, E., Zhang, Z., Kling, M. F., Huang, Z., Cryan, J. P., Marinelli, A. 2024

  View details for DOI 10.1038/s41566-024-01427-w

  View details for Web of Science ID 001220935700001

• Giant Terahertz Birefringence in an Ultrathin Anisotropic Semimetal. Nano letters Sie, E. J., Othman, M. A., Nyby, C. M., Pemmaraju, D., Garcia, C. A., Wang, Y., Guzelturk, B., Xia, C., Xiao, J., Poletayev, A., Ofori-Okai, B. K., Hoffmann, M. C., Park, S., Shen, X., Yang, J., Li, R., Reid, A. H., Weathersby, S., Muscher, P., Finney, N., Rhodes, D., Balicas, L., Nanni, E., Hone, J., Chueh, W., Devereaux, T. P., Narang, P., Heinz, T. F., Wang, X., Lindenberg, A. M. 2024

  Abstract

  Manipulating the polarization of light at the nanoscale is key to the development of next-generation optoelectronic devices. This is typically done via waveplates using optically anisotropic crystals, with thicknesses on the order of the wavelength. Here, using a novel ultrafast electron-beam-based technique sensitive to transient near fields at THz frequencies, we observe a giant anisotropy in the linear optical response in the semimetal WTe2 and demonstrate that one can tune the THz polarization using a 50 nm thick film, acting as a broadband wave plate with thickness 3 orders of magnitude smaller than the wavelength. The observed circular deflections of the electron beam are consistent with simulations tracking the trajectory of the electron beam in the near field of the THz pulse. This finding offers a promising approach to enable atomically thin THz polarization control using anisotropic semimetals and defines new approaches for characterizing THz near-field optical response at far-subwavelength length scales.

  View details for DOI 10.1021/acs.nanolett.4c00758

  View details for PubMedID 38717626

• Terahertz electric-field-driven dynamical multiferroicity in SrTiO3. Nature Basini, M., Pancaldi, M., Wehinger, B., Udina, M., Unikandanunni, V., Tadano, T., Hoffmann, M. C., Balatsky, A. V., Bonetti, S. 2024; 628 (8008): 534-539

  Abstract

  The emergence of collective order in matter is among the most fundamental and intriguing phenomena in physics. In recent years, the dynamical control and creation of novel ordered states of matter not accessible in thermodynamic equilibrium is receiving much attention1-6. The theoretical concept of dynamical multiferroicity has been introduced to describe the emergence of magnetization due to time-dependent electric polarization in non-ferromagnetic materials7,8. In simple terms, the coherent rotating motion of the ions in a crystal induces a magnetic moment along the axis of rotation. Here we provide experimental evidence of room-temperature magnetization in the archetypal paraelectric perovskite SrTiO3 due to this mechanism. We resonantly drive the infrared-active soft phonon mode with an intense circularly polarized terahertz electric field and detect the time-resolved magneto-optical Kerr effect. A simple model, which includes two coupled nonlinear oscillators whose forces and couplings are derived with ab initio calculations using self-consistent phonon theory at a finite temperature9, reproduces qualitatively our experimental observations. A quantitatively correct magnitude was obtained for the effect by also considering the phonon analogue of the reciprocal of the Einstein-de Haas effect, which is also called the Barnett effect, in which the total angular momentum from the phonon order is transferred to the electronic one. Our findings show a new path for the control of magnetism, for example, for ultrafast magnetic switches, by coherently controlling the lattice vibrations with light.

  View details for DOI 10.1038/s41586-024-07175-9

  View details for PubMedID 38600387

• Improved temporal resolution in ultrafast electron diffraction measurements through THz compression and time-stamping. Structural dynamics (Melville, N.Y.) Othman, M. A., Gabriel, A. E., Snively, E. C., Kozina, M. E., Shen, X., Ji, F., Lewis, S., Weathersby, S., Vasireddy, P., Luo, D., Wang, X., Hoffmann, M. C., Nanni, E. A. 2024; 11 (2): 024311

  Abstract

  We present an experimental demonstration of ultrafast electron diffraction (UED) with THz-driven electron bunch compression and time-stamping that enables UED probes with improved temporal resolution. Through THz-driven longitudinal bunch compression, a compression factor of approximately four is achieved. Moreover, the time-of-arrival jitter between the compressed electron bunch and a pump laser pulse is suppressed by a factor of three. Simultaneously, the THz interaction imparts a transverse spatiotemporal correlation on the electron distribution, which we utilize to further enhance the precision of time-resolved UED measurements. We use this technique to probe single-crystal gold nanofilms and reveal transient oscillations in the THz near fields with a temporal resolution down to 50 fs. These oscillations were previously beyond reach in the absence of THz compression and time-stamping.

  View details for DOI 10.1063/4.0000230

  View details for PubMedID 38655563

  View details for PubMedCentralID PMC11037933

• Monitoring the Evolution of Relative Product Populations at Early Times during a Photochemical Reaction. Journal of the American Chemical Society Figueira Nunes, J. P., Ibele, L. M., Pathak, S., Attar, A. R., Bhattacharyya, S., Boll, R., Borne, K., Centurion, M., Erk, B., Lin, M., Forbes, R. J., Goff, N., Hansen, C. S., Hoffmann, M., Holland, D. M., Ingle, R. A., Luo, D., Muvva, S. B., Reid, A. H., Rouzee, A., Rudenko, A., Saha, S. K., Shen, X., Venkatachalam, A. S., Wang, X., Ware, M. R., Weathersby, S. P., Wilkin, K., Wolf, T. J., Xiong, Y., Yang, J., Ashfold, M. N., Rolles, D., Curchod, B. F. 2024

  Abstract

  Identifying multiple rival reaction products and transient species formed during ultrafast photochemical reactions and determining their time-evolving relative populations are key steps toward understanding and predicting photochemical outcomes. Yet, most contemporary ultrafast studies struggle with clearly identifying and quantifying competing molecular structures/species among the emerging reaction products. Here, we show that mega-electronvolt ultrafast electron diffraction in combination with ab initio molecular dynamics calculations offer a powerful route to determining time-resolved populations of the various isomeric products formed after UV (266 nm) excitation of the five-membered heterocyclic molecule 2(5H)-thiophenone. This strategy provides experimental validation of the predicted high (50%) yield of an episulfide isomer containing a strained three-membered ring within 1 ps of photoexcitation and highlights the rapidity of interconversion between the rival highly vibrationally excited photoproducts in their ground electronic state.

  View details for DOI 10.1021/jacs.3c13046

  View details for PubMedID 38317439

• Publisher Correction: The persistence of memory in ionic conduction probed by nonlinear optics. Nature Poletayev, A. D., Hoffmann, M. C., Dawson, J. A., Teitelbaum, S. W., Trigo, M., Islam, M. S., Lindenberg, A. M. 2024

  View details for DOI 10.1038/s41586-024-07124-6

  View details for PubMedID 38291189

• The persistence of memory in ionic conduction probed by nonlinear optics. Nature Poletayev, A. D., Hoffmann, M. C., Dawson, J. A., Teitelbaum, S. W., Trigo, M., Islam, M. S., Lindenberg, A. M. 2024; 625 (7996): 691-696

  Abstract

  Predicting practical rates of transport in condensed phases enables the rational design of materials, devices and processes. This is especially critical to developing low-carbon energy technologies such as rechargeable batteries1-3. For ionic conduction, the collective mechanisms4,5, variation of conductivity with timescales6-8 and confinement9,10, and ambiguity in the phononic origin of translation11,12, call for a direct probe of the fundamental steps of ionic diffusion: ion hops. However, such hops are rare-event large-amplitude translations, and are challenging to excite and detect. Here we use single-cycle terahertz pumps to impulsively trigger ionic hopping in battery solid electrolytes. This is visualized by an induced transient birefringence, enabling direct probing of anisotropy in ionic hopping on the picosecond timescale. The relaxation of the transient signal measures the decay of orientational memory, and the production of entropy in diffusion. We extend experimental results using in silico transient birefringence to identify vibrational attempt frequencies for ion hopping. Using nonlinear optical methods, we probe ion transport at its fastest limit, distinguish correlated conduction mechanisms from a true random walk at the atomic scale, and demonstrate the connection between activated transport and the thermodynamics of information.

  View details for DOI 10.1038/s41586-023-06827-6

  View details for PubMedID 38267678

  View details for PubMedCentralID 5482052

• Experimental Plan for Terahertz Transport Using Overmoded Iris-Line Waveguide Othman, M. K., Fisher, A. S., Naji, A., Hoffmann, M. C., Huang, Z., IEEE IEEE. 2024

  View details for DOI 10.1109/IRMMW-THz60956.2024.10697605

  View details for Web of Science ID 001334520200081

• Femtosecond Electronic and Hydrogen Structural Dynamics in Ammonia Imaged with Ultrafast Electron Diffraction. Physical review letters Champenois, E. G., List, N. H., Ware, M., Britton, M., Bucksbaum, P. H., Cheng, X., Centurion, M., Cryan, J. P., Forbes, R., Gabalski, I., Hegazy, K., Hoffmann, M. C., Howard, A. J., Ji, F., Lin, M. F., Nunes, J. P., Shen, X., Yang, J., Wang, X., Martinez, T. J., Wolf, T. J. 2023; 131 (14): 143001

  Abstract

  Directly imaging structural dynamics involving hydrogen atoms by ultrafast diffraction methods is complicated by their low scattering cross sections. Here we demonstrate that megaelectronvolt ultrafast electron diffraction is sufficiently sensitive to follow hydrogen dynamics in isolated molecules. In a study of the photodissociation of gas phase ammonia, we simultaneously observe signatures of the nuclear and corresponding electronic structure changes resulting from the dissociation dynamics in the time-dependent diffraction. Both assignments are confirmed by ab initio simulations of the photochemical dynamics and the resulting diffraction observable. While the temporal resolution of the experiment is insufficient to resolve the dissociation in time, our results represent an important step towards the observation of proton dynamics in real space and time.

  View details for DOI 10.1103/PhysRevLett.131.143001

  View details for PubMedID 37862660

• Ultrafast X-Ray Scattering Reveals Composite Amplitude Collective Mode in the Weyl Charge Density Wave Material (TaSe_{4})_{2}I. Physical review letters Nguyen, Q. L., Duncan, R. A., Orenstein, G., Huang, Y., Krapivin, V., de la Peña, G., Ornelas-Skarin, C., Reis, D. A., Abbamonte, P., Bettler, S., Chollet, M., Hoffmann, M. C., Hurley, M., Kim, S., Kirchmann, P. S., Kubota, Y., Mahmood, F., Miller, A., Osaka, T., Qu, K., Sato, T., Shoemaker, D. P., Sirica, N., Song, S., Stanton, J., Teitelbaum, S. W., Tilton, S. E., Togashi, T., Zhu, D., Trigo, M. 2023; 131 (7): 076901

  Abstract

  We report ultrafast x-ray scattering experiments of the quasi-1D charge density wave (CDW) material (TaSe_{4})_{2}I following ultrafast infrared photoexcitation. From the time-dependent diffraction signal at the CDW sidebands we identify a 0.11 THz amplitude mode derived primarily from a transverse acoustic mode of the high-symmetry structure. From our measurements we determine that this mode interacts with the valence charge indirectly through another collective mode, and that the CDW system in (TaSe_{4})_{2}I has a composite nature supporting multiple dynamically active structural degrees of freedom.

  View details for DOI 10.1103/PhysRevLett.131.076901

  View details for PubMedID 37656841

• The 2023 terahertz science and technology roadmap JOURNAL OF PHYSICS D-APPLIED PHYSICS Leitenstorfer, A., Moskalenko, A. S., Kampfrath, T., Kono, J., Castro-Camus, E., Peng, K., Qureshi, N., Turchinovich, D., Tanaka, K., Markelz, A. G., Havenith, M., Hough, C., Joyce, H. J., Padilla, W. J., Zhou, B., Kim, K., Zhang, X., Jepsen, P., Dhillon, S., Vitiello, M., Linfield, E., Davies, A., Hoffmann, M. C., Lewis, R., Tonouchi, M., Klarskov, P., Seifert, T. S., Gerasimenko, Y. A., Mihailovic, D., Huber, R., Boland, J. L., Mitrofanov, O., Dean, P., Ellison, B. N., Huggard, P. G., Rea, S. P., Walker, C., Leisawitz, D. T., Gao, J., Li, C., Chen, Q., Valusis, G., Wallace, V. P., Pickwell-MacPherson, E., Shang, X., Hesler, J., Ridler, N., Renaud, C. C., Kallfass, I., Nagatsuma, T., Zeitler, J., Arnone, D., Johnston, M. B., Cunningham, J. 2023; 56 (22)

  View details for DOI 10.1088/1361-6463/acbe4c

  View details for Web of Science ID 000968966700001

• Rehybridization dynamics into the pericyclic minimum of an electrocyclic reaction imaged in real-time. Nature communications Liu, Y., Sanchez, D. M., Ware, M. R., Champenois, E. G., Yang, J., Nunes, J. P., Attar, A., Centurion, M., Cryan, J. P., Forbes, R., Hegazy, K., Hoffmann, M. C., Ji, F., Lin, M., Luo, D., Saha, S. K., Shen, X., Wang, X. J., Martinez, T. J., Wolf, T. J. 2023; 14 (1): 2795

  Abstract

  Electrocyclic reactions are characterized by the concerted formation and cleavage of both sigma and pi bonds through a cyclic structure. This structure is known as a pericyclic transition state for thermal reactions and a pericyclic minimum in the excited state for photochemical reactions. However, the structure of the pericyclic geometry has yet to be observed experimentally. We use a combination of ultrafast electron diffraction and excited state wavepacket simulations to image structural dynamics through the pericyclic minimum of a photochemical electrocyclic ring-opening reaction in the molecule alpha-terpinene. The structural motion into the pericyclic minimum is dominated by rehybridization of two carbon atoms, which is required for the transformation from two to three conjugated pi bonds. The sigma bond dissociation largely happens after internal conversion from the pericyclic minimum to the electronic ground state. These findings may be transferrable to electrocyclic reactions in general.

  View details for DOI 10.1038/s41467-023-38513-6

  View details for PubMedID 37202402

• Measurement of femtosecond dynamics of ultrafast electron beams through terahertz compression and time-stamping APPLIED PHYSICS LETTERS Othman, M. K., Gabriel, A. E., Snively, E. C., Kozina, M. E., Shen, X., Ji, F., Lewis, S., Weathersby, S., Vasireddy, P., Luo, D., Wang, X., Hoffmann, M. C., Nanni, E. A. 2023; 122 (14)

  View details for DOI 10.1063/5.0134733

  View details for Web of Science ID 000964331000010

• Terahertz-Driven Local Dipolar Correlation in a Quantum Paraelectric. Physical review letters Cheng, B., Kramer, P. L., Shen, Z. X., Hoffmann, M. C. 2023; 130 (12): 126902

  Abstract

  Light-induced ferroelectricity in quantum paraelectrics is a new avenue of achieving dynamic stabilization of hidden orders in quantum materials. In this Letter, we explore the possibility of driving a transient ferroelectric phase in the quantum paraelectric KTaO_{3} via intense terahertz excitation of the soft mode. We observe a long-lived relaxation in the terahertz-driven second harmonic generation (SHG) signal that lasts up to 20 ps at 10 K, which may be attributed to light-induced ferroelectricity. Through analyzing the terahertz-induced coherent soft-mode oscillation and finding its hardening with fluence well described by a single-well potential, we demonstrate that intense terahertz pulses up to 500  kV/cm cannot drive a global ferroelectric phase in KTaO_{3}. Instead, we find the unusual long-lived relaxation of the SHG signal comes from a terahertz-driven moderate dipolar correlation between the defect-induced local polar structures. We discuss the impact of our findings on current investigations of the terahertz-induced ferroelectric phase in quantum paraelectrics.

  View details for DOI 10.1103/PhysRevLett.130.126902

  View details for PubMedID 37027861

• Ultrafast Optomechanical Strain in Layered GeS. Nano letters Luo, D., Zhang, B., Sie, E. J., Nyby, C. M., Fan, Q., Shen, X., Reid, A. H., Hoffmann, M. C., Weathersby, S., Wen, J., Qian, X., Wang, X., Lindenberg, A. M. 2023

  Abstract

  Strong coupling between light and mechanical strain forms the foundation for next-generation optical micro- and nano-electromechanical systems. Such optomechanical responses in two-dimensional materials present novel types of functionalities arising from the weak van der Waals bond between atomic layers. Here, by using structure-sensitive megaelectronvolt ultrafast electron diffraction, we report the experimental observation of optically driven ultrafast in-plane strain in the layered group IV monochalcogenide germanium sulfide (GeS). Surprisingly, the photoinduced structural deformation exhibits strain amplitudes of order 0.1% with a 10 ps fast response time and a significant in-plane anisotropy between zigzag and armchair crystallographic directions. Rather than arising due to heating, experimental and theoretical investigations suggest deformation potentials caused by electronic density redistribution and converse piezoelectric effects generated by photoinduced electric fields are the dominant contributors to the observed dynamic anisotropic strains. Our observations define new avenues for ultrafast optomechanical control and strain engineering within functional devices.

  View details for DOI 10.1021/acs.nanolett.2c05048

  View details for PubMedID 36898060

• Lightwave-driven electron emission for polarity-sensitive terahertz beam profiling APL PHOTONICS Lange, S., Hoffmann, M. C., Jepsen, P. 2023; 8 (1)

  View details for DOI 10.1063/5.0125947

  View details for Web of Science ID 000923543500001

• Terahertz Pump/X-ray Probe Experiments At LCLS Hoffmann, M. C., IEEE IEEE. 2023

  View details for DOI 10.1109/IRMMW-THz57677.2023.10298857

  View details for Web of Science ID 001098999800008

• Spatiotemporal Imaging of Near-Fields from a Tilted Pulse Front THz Source Gabriel, A. E., Othman, M. K., Hoffmann, M. C., Nanni, E. A., IEEE IEEE. 2023

  View details for DOI 10.1109/IRMMW-THz57677.2023.10299154

  View details for Web of Science ID 001098999800303

• Ultrafast modification of the electronic structure of a correlated insulator PHYSICAL REVIEW RESEARCH Granaes, O., Vaskivskyi, I., Wang, X., Thunstroem, P., Ghimire, S., Knut, R., Soederstroem, J., Kjellsson, L., Turenne, D., Engel, R. Y., Beye, M., Lu, J., Higley, D. J., Reid, A. H., Schlotter, W., Coslovich, G., Hoffmann, M., Kolesov, G., Schissler-Langeheine, C., Styervoyedov, A., Tancogne-Dejean, N., Sentef, M. A., Reis, D. A., Rubio, A., Parkin, S. P., Karis, O., Rubensson, J., Eriksson, O., Dirr, H. A. 2022; 4 (3)

  View details for DOI 10.1103/PhysRevResearch.4.L032030

  View details for Web of Science ID 000856584000004

• Observation of photo-induced plasmon-phonon coupling in PbTe via ultrafast x-ray scattering. Structural dynamics (Melville, N.Y.) Jiang, M. P., Fahy, S., Hauber, A., Murray, E. D., Savic, I., Bray, C., Clark, J. N., Henighan, T., Kozina, M., Lindenberg, A. M., Zalden, P., Chollet, M., Glownia, J. M., Hoffmann, M. C., Sato, T., Zhu, D., Delaire, O., May, A. F., Sales, B. C., Merlin, R., Trigo, M., Reis, D. A. 2022; 9 (2): 024301

  Abstract

  We report the observation of photo-induced plasmon-phonon coupled modes in the group IV-VI semiconductor PbTe using ultrafast x-ray diffuse scattering at the Linac Coherent Light Source. We measure the near-zone-center excited-state dispersion of the heavily screened longitudinal optical (LO) phonon branch as extracted from differential changes in x-ray diffuse scattering intensity following above bandgap photoexcitation. We suggest that upon photoexcitation, the LO phonon-plasmon coupled (LOPC) modes themselves become coupled to longitudinal acoustic modes that drive electron band shifts via acoustic deformation potentials and possibly to low-energy single-particle excitations within the plasma and that these couplings give rise to displacement-correlations that oscillate in time with a period given effectively by the heavily screened LOPC frequency.

  View details for DOI 10.1063/4.0000133

  View details for PubMedID 35311000

• Ultrafast electron dynamics in platinum and gold thin films driven by optical and terahertz fields APPLIED PHYSICS LETTERS Unikandanunni, V., Rigoni, F., Hoffmann, M. C., Vavassori, P., Urazhdin, S., Bonetti, S. 2022; 120 (2)

  View details for DOI 10.1063/5.0068086

  View details for Web of Science ID 000791375600005

• Spatiotemporal Measurement of THz Near-Fields Using Electro-Optic Sampling Gabriel, A. E., Othman, M. K., Hoffmann, M. C., Nanni, E. A., IEEE IEEE. 2022

  View details for DOI 10.1109/IRMMW-THz50927.2022.9895825

  View details for Web of Science ID 000865953000311

• Subterahertz collective dynamics of polar vortices. Nature Li, Q., Stoica, V. A., Pasciak, M., Zhu, Y., Yuan, Y., Yang, T., McCarter, M. R., Das, S., Yadav, A. K., Park, S., Dai, C., Lee, H. J., Ahn, Y., Marks, S. D., Yu, S., Kadlec, C., Sato, T., Hoffmann, M. C., Chollet, M., Kozina, M. E., Nelson, S., Zhu, D., Walko, D. A., Lindenberg, A. M., Evans, P. G., Chen, L., Ramesh, R., Martin, L. W., Gopalan, V., Freeland, J. W., Hlinka, J., Wen, H. 2021; 592 (7854): 376–80

  Abstract

  The collective dynamics of topological structures1-6 are of interest from both fundamental and applied perspectives. For example, studies of dynamical properties of magnetic vortices and skyrmions3,4 have not only deepened our understanding of many-body physics but also offered potential applications in data processing and storage7. Topological structures constructed from electrical polarization, rather than electron spin, have recently been realized in ferroelectric superlattices5,6, and these are promising for ultrafast electric-field control of topological orders. However, little is known about the dynamics underlying the functionality of such complex extended nanostructures. Here, using terahertz-field excitation and femtosecond X-ray diffraction measurements, we observe ultrafast collective polarization dynamics that are unique to polar vortices, with orders-of-magnitude higher frequencies and smaller lateral size than those of experimentally realized magnetic vortices3. A previously unseen tunable mode, hereafter referred to as a vortexon, emerges in the form of transient arrays of nanoscale circular patterns of atomic displacements, which reverse their vorticity on picosecond timescales. Its frequency is considerably reduced (softened) at a critical strain, indicating a condensation (freezing) of structural dynamics. We use first-principles-based atomistic calculations and phase-field modelling to reveal the microscopic atomic arrangements and corroborate the frequencies of the vortex modes. The discovery of subterahertz collective dynamics in polar vortices opens opportunities for electric-field-driven data processing in topological structures with ultrahigh speed and density.

  View details for DOI 10.1038/s41586-021-03342-4

  View details for PubMedID 33854251

• Ultrafast structural dynamics of strongly-THz-driven materials Hoffmann, M. C., IEEE IEEE. 2021

  View details for DOI 10.1109/CLEO/Europe-EQEC52157.2021.9542729

  View details for Web of Science ID 000728078301051

• Enabling high repetition rate nonlinear THz science with a kilowatt-class sub-100 fs laser source OPTICS EXPRESS Kramer, P. L., Windeler, M. R., Mecseki, K., Champenois, E. G., Hoffmann, M. C., Tavella, F. 2020; 28 (11): 16951–67

  Abstract

  Manipulating the atomic and electronic structure of matter with strong terahertz (THz) fields while probing the response with ultrafast pulses at x-ray free electron lasers (FELs) has offered unique insights into a multitude of physical phenomena in solid state and atomic physics. Recent upgrades of x-ray FEL facilities are pushing to much higher repetition rates, enabling unprecedented signal-to-noise ratio for pump probe experiments. This requires the development of suitable THz pump sources that are able to deliver intense pulses at compatible repetition rates. Here we present a high-power laser-driven THz source based on optical rectification in LiNbO3 using tilted pulse front pumping. Our source is driven by a kilowatt-level Yb:YAG amplifier system operating at 100 kHz repetition rate and employing nonlinear spectral broadening and recompression to achieve sub-100 fs pulses with pulse energies up to 7 mJ that are necessary for high THz conversion efficiency and peak field strength. We demonstrate a maximum of 144 mW average THz power (1.44 μJ pulse energy), consisting of single-cycle pulses centered at 0.6 THz with a peak electric field strength exceeding 150 kV/cm. These high field pulses open up a range of possibilities for nonlinear time-resolved THz experiments at unprecedented rates.

  View details for DOI 10.1364/OE.389653

  View details for Web of Science ID 000542303000096

  View details for PubMedID 32549507

• Ultrafast Dynamics of a Terahertz Dual-Fed Relativistic Electron Bunch Compressor Othman, M. K., Snively, E. C., Kozina, M. E., Kramer, P. L., Shen, X., Ji, F., Weathersby, S., Wang, X. J., Hoffmann, M. C., Nanni, E. A., IEEE IEEE. 2020

  View details for Web of Science ID 000612090000481

• THz-driven bunch compression for varying electron beam energy Snively, E., Othman, M. K., Kozina, M., Ofori-Okai, B., Weathersby, S., Park, S., Shen, X., Wang, X., Hoffmann, M., Li, R., Nanni, E., IEEE IEEE. 2020

  View details for DOI 10.1109/IRMMW-THZ46771.2020.9370507

  View details for Web of Science ID 000662887600118

• Generation of high-field single-cycle terahertz pulses at 100 kHz Kramer, P. L., Hoffmann, M. C., Tavella, F., IEEE IEEE. 2020

  View details for Web of Science ID 000612090001010

• Nonlinear Magnetization Dynamics Driven by Strong Terahertz Fields. Physical review letters Hudl, M., d'Aquino, M., Pancaldi, M., Yang, S., Samant, M. G., Parkin, S. S., Durr, H. A., Serpico, C., Hoffmann, M. C., Bonetti, S. 2019; 123 (19): 197204

  Abstract

  We present a comprehensive experimental and numerical study of magnetization dynamics in a thin metallic film triggered by single-cycle terahertz pulses of 20MV/m electric field amplitude and 1ps duration. The experimental dynamics is probed using the femtosecond magneto-optical Kerr effect, and it is reproduced numerically using macrospin simulations. The magnetization dynamics can be decomposed in three distinct processes: a coherent precession of the magnetization around the terahertz magnetic field, an ultrafast demagnetization that suddenly changes the anisotropy of the film, and a uniform precession around the equilibrium effective field that is relaxed on the nanosecond time scale, consistent with a Gilbert damping process. Macrospin simulations quantitatively reproduce the observed dynamics, and allow us to predict that novel nonlinear magnetization dynamics regimes can be attained with existing tabletop terahertz sources.

  View details for DOI 10.1103/PhysRevLett.123.197204

  View details for PubMedID 31765192

• Dynamical Slowing-Down in an Ultrafast Photoinduced Phase Transition. Physical review letters Zong, A., Dolgirev, P. E., Kogar, A., Ergeçen, E., Yilmaz, M. B., Bie, Y. Q., Rohwer, T., Tung, I. C., Straquadine, J., Wang, X., Yang, Y., Shen, X., Li, R., Yang, J., Park, S., Hoffmann, M. C., Ofori-Okai, B. K., Kozina, M. E., Wen, H., Wang, X., Fisher, I. R., Jarillo-Herrero, P., Gedik, N. 2019; 123 (9): 097601

  Abstract

  Complex systems, which consist of a large number of interacting constituents, often exhibit universal behavior near a phase transition. A slowdown of certain dynamical observables is one such recurring feature found in a vast array of contexts. This phenomenon, known as critical slowing-down, is well studied mostly in thermodynamic phase transitions. However, it is less understood in highly nonequilibrium settings, where the time it takes to traverse the phase boundary becomes comparable to the timescale of dynamical fluctuations. Using transient optical spectroscopy and femtosecond electron diffraction, we studied a photoinduced transition of a model charge-density-wave (CDW) compound LaTe_{3}. We observed that it takes the longest time to suppress the order parameter at the threshold photoexcitation density, where the CDW transiently vanishes. This finding can be captured by generalizing the time-dependent Landau theory to a system far from equilibrium. The experimental observation and theoretical understanding of dynamical slowing-down may offer insight into other general principles behind nonequilibrium phase transitions in many-body systems.

  View details for DOI 10.1103/PhysRevLett.123.097601

  View details for PubMedID 31524450

• Dynamical Slowing-Down in an Ultrafast Photoinduced Phase Transition PHYSICAL REVIEW LETTERS Zong, A., Dolgirev, P. E., Kogar, A., Ergecen, E., Yilmaz, M. B., Bie, Y., Rohwer, T., Tung, I., Straquadine, J., Wang, X., Yang, Y., Shen, X., Li, R., Yang, J., Park, S., Hoffmann, M. C., Ofori-Okai, B. K., Kozina, M. E., Wen, H., Wang, X., Fisher, I. R., Jarillo-Herrero, P., Gedik, N. 2019; 123 (9)

  View details for DOI 10.1103/PhysRevLett.123.097601

  View details for Web of Science ID 000483048500015

• Parallel-plate waveguides for terahertz-driven MeV electron bunch compression OPTICS EXPRESS Othman, M. K., Hoffmann, M. C., Kozina, M. E., Wang, X. J., Li, R. K., Nanni, E. A. 2019; 27 (17): 23791–800

  View details for DOI 10.1364/OE.27.023791

  View details for Web of Science ID 000482098300013

• Terahertz-pump Experiments On Complex Solids at X-ray FELs Hoffmann, M. C., Kozina, M. E., Razeghi, M., Baranov, A. N. SPIE-INT SOC OPTICAL ENGINEERING. 2019

  View details for DOI 10.1117/12.2322169

  View details for Web of Science ID 000461341400004

• An Ultrafast Symmetry Switch in a Weyl Semimetal Nature Sie, E. J., et al 2019; 565, 61

  View details for DOI 10.1038/s41586-018-0809-4

• THz-driven bunch compression and timing stabilization of a relativistic electron beam Snively, E., Othman, M., Kozinal, M., Ofori-Okai, B., Weathersby, S., Park, S., Shen, X., Wang, X., Hoffmann, M., Li, R., Nanni, E., IEEE IEEE. 2019

  View details for Web of Science ID 000591783800140

• Parallel-Plate THz Waveguides for Relativistic Electron Bunch Compression Othman, M. K., Hoffmann, M. C., Li, R., Nanni, E. A., Wang, X. J., IEEE IEEE. 2019

  View details for Web of Science ID 000482226303003

• Terahertz Kerr Effect in beta-Alumina Ion Conductors Poletayev, A. D., Hoffmann, M. C., Teitelbaum, S. W., Trigo, M., Chueh, W. C., Lindenberg, A. M., IEEE IEEE. 2019

  View details for Web of Science ID 000482226301054

• THz-Pump UED-Probe on a Topological Weyl Semimetal Sie, E. J., Nyby, C. M., Pemmaraju, C. D., Park, S., Shen, X., Yang, J., Hoffmann, M. C., Ofori-Okai, B. K., Li, R., Reid, A. H., Weathersby, S., Mannebach, E., Finney, N., Rhodes, D., Chenet, D., Antony, A., Balicas, L., Hone, J., Devereaux, T. P., Heinz, T. F., Wang, X., Lindenberg, A. M., IEEE IEEE. 2019

  View details for Web of Science ID 000482226301297

• Phonon-Suppressed Auger Scattering of Charge Carriers in Defective Two-Dimensional Transition Metal Dichalcogenides. Nano letters Li, L. n., Lin, M. F., Zhang, X. n., Britz, A. n., Krishnamoorthy, A. n., Ma, R. n., Kalia, R. K., Nakano, A. n., Vashishta, P. n., Ajayan, P. n., Hoffmann, M. C., Fritz, D. M., Bergmann, U. n., Prezhdo, O. V. 2019

  Abstract

  Two-dimensional transition metal dichalcogenides (TMDs) draw strong interest in materials science, with applications in optoelectronics and many other fields. Good performance requires high carrier concentrations and long lifetimes. However, high concentrations accelerate energy exchange between charged particles by Auger-type processes, especially in TMDs where many-body interactions are strong, thus facilitating carrier trapping. We report time-resolved optical pump-THz probe measurements of carrier lifetimes as a function of carrier density. Surprisingly, the lifetime reduction with increased density is very weak. It decreases only by 20% when we increase the pump fluence 100 times. This unexpected feature of the Auger process is rationalized by our time-domain ab initio simulations. The simulations show that phonon-driven trapping competes successfully with the Auger process. On the one hand, trap states are relatively close to band edges, and phonons accommodate efficiently the electronic energy during the trapping. On the other hand, trap states localize around defects, and the overlap of trapped and free carriers is small, decreasing carrier-carrier interactions. At low carrier densities, phonons provide the main charge trapping mechanism, decreasing carrier lifetimes compared to defect-free samples. At high carrier densities, phonons suppress Auger processes and lower the dependence of the trapping rate on carrier density. Our results provide theoretical insights into the diverse roles played by phonons and Auger processes in TMDs and generate guidelines for defect engineering to improve device performance at high carrier densities.

  View details for DOI 10.1021/acs.nanolett.9b02005

  View details for PubMedID 31434484

• An ultrafast symmetry switch in a Weyl semimetal. Nature Sie, E. J., Nyby, C. M., Pemmaraju, C. D., Park, S. J., Shen, X. n., Yang, J. n., Hoffmann, M. C., Ofori-Okai, B. K., Li, R. n., Reid, A. H., Weathersby, S. n., Mannebach, E. n., Finney, N. n., Rhodes, D. n., Chenet, D. n., Antony, A. n., Balicas, L. n., Hone, J. n., Devereaux, T. P., Heinz, T. F., Wang, X. n., Lindenberg, A. M. 2019; 565 (7737): 61–66

  Abstract

  Topological quantum materials exhibit fascinating properties1-3, with important applications for dissipationless electronics and fault-tolerant quantum computers4,5. Manipulating the topological invariants in these materials would allow the development of topological switching applications analogous to switching of transistors6. Lattice strain provides the most natural means of tuning these topological invariants because it directly modifies the electron-ion interactions and potentially alters the underlying crystalline symmetry on which the topological properties depend7-9. However, conventional means of applying strain through heteroepitaxial lattice mismatch10 and dislocations11 are not extendable to controllable time-varying protocols, which are required in transistors. Integration into a functional device requires the ability to go beyond the robust, topologically protected properties of materials and to manipulate the topology at high speeds. Here we use crystallographic measurements by relativistic electron diffraction to demonstrate that terahertz light pulses can be used to induce terahertz-frequency interlayer shear strain with large strain amplitude in the Weyl semimetal WTe2, leading to a topologically distinct metastable phase. Separate nonlinear optical measurements indicate that this transition is associated with a symmetry change to a centrosymmetric, topologically trivial phase. We further show that such shear strain provides an ultrafast, energy-efficient way of inducing robust, well separated Weyl points or of annihilating all Weyl points of opposite chirality. This work demonstrates possibilities for ultrafast manipulation of the topological properties of solids and for the development of a topological switch operating at terahertz frequencies.

  View details for PubMedID 30602749

• Disentangling Transient Charge Density and Metal-Ligand Covalency in Photoexcited Ferricyanide with Femtosecond Resonant Inelastic Soft X-ray Scattering JOURNAL OF PHYSICAL CHEMISTRY LETTERS Jay, R. M., Norell, J., Eckert, S., Hantschmann, M., Beye, M., Kennedy, B., Quevedo, W., Schlotter, W. F., Dakovski, G. L., Minitti, M. P., Hoffmann, M. C., Mitra, A., Moeller, S. P., Nordlund, D., Zhang, W., Liang, H. W., Kunnus, K., Kubicek, K., Techert, S. A., Lundberg, M., Wernet, P., Gaffney, K., Odelius, M., Foehlisch, A. 2018; 9 (12): 3538–43

  Abstract

  Soft X-ray spectroscopies are ideal probes of the local valence electronic structure of photocatalytically active metal sites. Here, we apply the selectivity of time-resolved resonant inelastic X-ray scattering at the iron L-edge to the transient charge distribution of an optically excited charge-transfer state in aqueous ferricyanide. Through comparison to steady-state spectra and quantum chemical calculations, the coupled effects of valence-shell closing and ligand-hole creation are experimentally and theoretically disentangled and described in terms of orbital occupancy, metal-ligand covalency, and ligand field splitting, thereby extending established steady-state concepts to the excited-state domain. π-Back-donation is found to be mainly determined by the metal site occupation, whereas the ligand hole instead influences σ-donation. Our results demonstrate how ultrafast resonant inelastic X-ray scattering can help characterize local charge distributions around catalytic metal centers in short-lived charge-transfer excited states, as a step toward future rationalization and tailoring of photocatalytic capabilities of transition-metal complexes.

  View details for PubMedID 29888918

• Anti-reflection coating design for metallic terahertz meta-materials OPTICS EXPRESS Pancaldi, M., Freeman, R., Hudl, M., Hoffmann, M. C., Urazhdin, S., Vavassori, P., Bonetti, S. 2018; 26 (3): 2917–27

  Abstract

  We demonstrate a silicon-based, single-layer anti-reflection coating that suppresses the reflectivity of metals at near-infrared frequencies, enabling optical probing of nano-scale structures embedded in highly reflective surroundings. Our design does not affect the interaction of terahertz radiation with metallic structures that can be used to achieve terahertz near-field enhancement. We have verified the functionality of the design by calculating and measuring the reflectivity of both infrared and terahertz radiation from a silicon/gold double layer as a function of the silicon thickness. We have also fabricated the unit cell of a terahertz meta-material, a dipole antenna comprising two 20-nm thick extended gold plates separated by a 2 μm gap, where the terahertz field is locally enhanced. We used the time-domain finite element method to demonstrate that such near-field enhancement is preserved in the presence of the anti-reflection coating. Finally, we performed magneto-optical Kerr effect measurements on a single 3-nm thick, 1-μm wide magnetic wire placed in the gap of such a dipole antenna. The wire only occupies 2% of the area probed by the laser beam, but its magneto-optical response can be clearly detected. Our design paves the way for ultrafast time-resolved studies, using table-top femtosecond near-infrared lasers, of dynamics in nano-structures driven by strong terahertz radiation.

  View details for DOI 10.1364/OE.26.002917

  View details for Web of Science ID 000425365900069

  View details for PubMedID 29401825

• Development of a THz Pump MeV Ultrafast Electron Diffraction Probe Apparatus Ofori-Okai, B. K., Hoffmann, M. C., Reid, A. H., Li, R., Shen, X., Yang, J., Zheng, Q., Park, S., Mannenbach, E. M., Weathersby, S. P., Edstrom, S., Polzin, W., Lindenberg, A. M., Glenzer, S. H., Wang, X., IEEE IEEE. 2018

  View details for Web of Science ID 000526031002462

• Single-Shot Electro-Optic Measurement of Mid-Infrared Pulses Kozina, M. E., Hoffmann, M. C., IEEE IEEE. 2018

  View details for Web of Science ID 000526031003024

• Anti-reflection coating design for metallic terahertz meta-materials Pancaldi, M., Freeman, R., Hudl, M., Hoffmann, M. C., Urazhdin, S., Vavassori, P., Bonetti, S., IEEE IEEE. 2018

  View details for Web of Science ID 000526031002145

• Self-referenced single-shot THz detection OPTICS EXPRESS Russell, B. K., Ofori-Okai, B. K., Chen, Z., Hoffmann, M. C., Tsui, Y. Y., Glenzer, S. H. 2017; 25 (14): 16140–50

  Abstract

  We demonstrate a self-referencing method to reduce noise in a single-shot terahertz detection scheme. By splitting a single terahertz pulse and using a reflective echelon, both the signal and reference terahertz time-domain waveforms were measured using one laser pulse. Simultaneous acquisition of these waveforms significantly reduces noise originating from shot-to-shot fluctuations. We show that correlation function based referencing, which is not limited to polarization dependent measurements, can achieve a noise floor that is comparable to state-of-the-art polarization-gated balanced detection. Lastly, we extract the DC conductivity of a 30 nm free-standing gold film using a single THz pulse. The measured value of σ0 = 1.3 ± 0.4 × 107 S m-1 is in good agreement with the value measured by four-point probe, indicating the viability of this method for measuring dynamical changes and small signals.

  View details for DOI 10.1364/OE.25.016140

  View details for Web of Science ID 000407815100049

  View details for PubMedID 28789123

• The 2017 terahertz science and technology roadmap JOURNAL OF PHYSICS D-APPLIED PHYSICS Dhillon, S. S., Vitiello, M. S., Linfield, E. H., Davies, A. G., Hoffmann, M. C., Booske, J., Paoloni, C., Gensch, M., Weightman, P., Williams, G. P., Castro-Camus, E., Cumming, D. S., Simoens, F., Escorcia-Carranza, I., Grant, J., Lucyszyn, S., Kuwata-Gonokami, M., Konishi, K., Koch, M., Schmuttenmaer, C. A., Cocker, T. L., Huber, R., Markelz, A. G., Taylor, Z. D., Wallace, V. P., Zeitler, J., Sibik, J., Korter, T. M., Ellison, B., Rea, S., Goldsmith, P., Cooper, K. B., Appleby, R., Pardo, D., Huggard, P. G., Krozer, V., Shams, H., Fice, M., Renaud, C., Seeds, A., Stoehr, A., Naftaly, M., Ridler, N., Clarke, R., Cunningham, J. E., Johnston, M. B. 2017; 50 (4)

  View details for DOI 10.1088/1361-6463/50/4/043001

  View details for Web of Science ID 000392153700001

• Single-shot terahertz time-domain spectroscopy in pulsed high magnetic fields OPTICS EXPRESS Noe, G., Katayama, I., Katsutani, F., Allred, J. J., Horowitz, J. A., Sullivan, D. M., Zhang, Q., Sekiguchi, F., Woods, G. L., Hoffmann, M. C., Nojiri, H., Takeda, J., Kono, J. 2016; 24 (26): 30328–37

  Abstract

  We have developed a single-shot terahertz time-domain spectrometer to perform optical-pump/terahertz-probe experiments in pulsed, high magnetic fields up to 30 T. The single-shot detection scheme for measuring a terahertz waveform incorporates a reflective echelon to create time-delayed beamlets across the intensity profile of the optical gate beam before it spatially and temporally overlaps with the terahertz radiation in a ZnTe detection crystal. After imaging the gate beam onto a camera, we can retrieve the terahertz time-domain waveform by analyzing the resulting image. To demonstrate the utility of our technique, we measured cyclotron resonance absorption of optically excited carriers in the terahertz frequency range in intrinsic silicon at high magnetic fields, with results that agree well with published values.

  View details for DOI 10.1364/OE.24.030328

  View details for Web of Science ID 000390809100103

  View details for PubMedID 28059309

• Femtosecond X-ray magnetic circular dichroism absorption spectroscopy at an X-ray free electron laser REVIEW OF SCIENTIFIC INSTRUMENTS Higley, D. J., Hirsch, K., Dakovski, G. L., Jal, E., Yuan, E., Liu, T., Lutman, A. A., MacArthur, J. P., Arenholz, E., Chen, Z., Coslovich, G., Denes, P., Granitzka, P. W., Hart, P., Hoffmann, M. C., Joseph, J., Le Guyader, L., Mitra, A., Moeller, S., Ohldag, H., Seaberg, M., Shafer, P., Stoehr, J., Tsukamoto, A., Nuhn, H., Reid, A. H., Duerr, H. A., Schlotter, W. F. 2016; 87 (3)

  Abstract

  X-ray magnetic circular dichroism spectroscopy using an X-ray free electron laser is demonstrated with spectra over the Fe L(3,2)-edges. The high brightness of the X-ray free electron laser combined with high accuracy detection of incident and transmitted X-rays enables ultrafast X-ray magnetic circular dichroism studies of unprecedented sensitivity. This new capability is applied to a study of all-optical magnetic switching dynamics of Fe and Gd magnetic sublattices in a GdFeCo thin film above its magnetization compensation temperature.

  View details for DOI 10.1063/1.4944410

  View details for Web of Science ID 000373713300011

  View details for PubMedID 27036761

• Time-domain electric field enhancement on micrometer scale in coupled split ring resonator upon terahertz radiation Lange, S. L., Iwaszczuk, K., Hoffmann, M., Broeng, J., Jepsen, P. U., IEEE IEEE. 2016

  View details for Web of Science ID 000391406200364

• Excitation of Coherent Oscillations in Underdoped Cuprate Superconductors by Intense THz Pulses Hoffmann, M. C., Lee, W., Dakovski, G. L., Turner, J. J., Gerber, S. M., Bonn, D., Hardy, W., Liang, R., Salluzzo, M., Rafailov, M. K., Mazur, E. SPIE-INT SOC OPTICAL ENGINEERING. 2016

  View details for DOI 10.1117/12.2224993

  View details for Web of Science ID 000381933900025

• Direct observation of lattice motion driven by strong THz pulses Kozina, M. E., Zhu, D., Glownia, J. M., van Driel, T., Bonetti, S., Staub, U., Hoffmann, M. C., IEEE IEEE. 2016

  View details for Web of Science ID 000391286401354

• Ultrafast Terahertz Gating of the Polarization and Giant Nonlinear Optical Response in BiFeO3 Thin Films ADVANCED MATERIALS Chen, F., Goodfellow, J., Liu, S., Grinberg, I., Hoffmann, M. C., Damodaran, A. R., Zhu, Y., Zalden, P., Zhang, X., Takeuchi, I., Rappe, A. M., Martin, L. W., Wen, H., Lindenberg, A. M. 2015; 27 (41): 6371-?

  Abstract

  Terahertz pulses are applied as an all-optical bias to ferroelectric thin-film BiFeO3 while monitoring the time-dependent ferroelectric polarization through its nonlinear optical response. Modulations in the intensity of the second harmonic light generated by the film correspond to on-off ratios of 220× gateable on femtosecond timescales. Polarization modulations comparable to the built-in static polarization are observed.

  View details for DOI 10.1002/adma.201502975

  View details for Web of Science ID 000364343700009

• Ultrafast Terahertz Gating of the Polarization and Giant Nonlinear Optical Response in BiFeO3 Thin Films. Advanced materials (Deerfield Beach, Fla.) Chen, F., Goodfellow, J., Liu, S., Grinberg, I., Hoffmann, M. C., Damodaran, A. R., Zhu, Y., Zalden, P., Zhang, X., Takeuchi, I., Rappe, A. M., Martin, L. W., Wen, H., Lindenberg, A. M. 2015; 27 (41): 6371-5

  Abstract

  Terahertz pulses are applied as an all-optical bias to ferroelectric thin-film BiFeO3 while monitoring the time-dependent ferroelectric polarization through its nonlinear optical response. Modulations in the intensity of the second harmonic light generated by the film correspond to on-off ratios of 220× gateable on femtosecond timescales. Polarization modulations comparable to the built-in static polarization are observed.

  View details for DOI 10.1002/adma.201502975

  View details for PubMedID 26389651

• Direct observation of ultrafast collective motions in CO myoglobin upon ligand dissociation SCIENCE Barends, T. M., Foucar, L., Ardevol, A., Nass, K., Aquila, A., Botha, S., Doak, R., Falahati, K., Hartmann, E., Hilpert, M., Heinz, M., Hoffmann, M. C., Koefinger, J., Koglin, J. E., Kovacsova, G., Liang, M., Milathianaki, D., Lemke, H. T., Reinstein, J., Roome, C. M., Shoeman, R. L., Williams, G. J., Burghardt, I., Hummer, G., Boutet, S., Schlichting, I. 2015; 350 (6259): 445–50

  Abstract

  The hemoprotein myoglobin is a model system for the study of protein dynamics. We used time-resolved serial femtosecond crystallography at an x-ray free-electron laser to resolve the ultrafast structural changes in the carbonmonoxy myoglobin complex upon photolysis of the Fe-CO bond. Structural changes appear throughout the protein within 500 femtoseconds, with the C, F, and H helices moving away from the heme cofactor and the E and A helices moving toward it. These collective movements are predicted by hybrid quantum mechanics/molecular mechanics simulations. Together with the observed oscillations of residues contacting the heme, our calculations support the prediction that an immediate collective response of the protein occurs upon ligand dissociation, as a result of heme vibrational modes coupling to global modes of the protein.

  View details for PubMedID 26359336

• Enhanced coherent oscillations in the superconducting state of underdoped YBa2Cu3O6+x induced via ultrafast terahertz excitation PHYSICAL REVIEW B Dakovski, G. L., Lee, W., Hawthorn, D. G., Garner, N., Bonn, D., Hardy, W., Liang, R., Hoffmann, M. C., Turner, J. J. 2015; 91 (22)

  View details for DOI 10.1103/PhysRevB.91.220506

  View details for Web of Science ID 000356791700002

• Combining THz laser excitation with resonant soft X-ray scattering at the Linac Coherent Light Source JOURNAL OF SYNCHROTRON RADIATION Turner, J. J., Dakovski, G. L., Hoffmann, M. C., Hwang, H. Y., Zarem, A., Schlotter, W. F., Moeller, S., Minitti, M. P., Staub, U., Johnson, S., Mitra, A., Swiggers, M., Noonan, P., Curiel, G. I., Holmes, M. 2015; 22: 621-625

  Abstract

  This paper describes the development of new instrumentation at the Linac Coherent Light Source for conducting THz excitation experiments in an ultra high vacuum environment probed by soft X-ray diffraction. This consists of a cantilevered, fully motorized mirror system which can provide 600 kV cm(-1) electric field strengths across the sample and an X-ray detector that can span the full Ewald sphere with in-vacuum motion. The scientific applications motivated by this development, the details of the instrument, and spectra demonstrating the field strengths achieved using this newly developed system are discussed.

  View details for DOI 10.1107/S1600577515005998

  View details for Web of Science ID 000353920300024

  View details for PubMedID 25931077

  View details for PubMedCentralID PMC4416678

• Optical laser systems at the Linac Coherent Light Source JOURNAL OF SYNCHROTRON RADIATION Minitti, M. P., Robinson, J. S., Coffee, R. N., Edstrom, S., Gilevich, S., Glownia, J. M., Granados, E., Hering, P., Hoffmann, M. C., Miahnahri, A., Milathianaki, D., Polzin, W., Ratner, D., Tavella, F., Vetter, S., Welch, M., White, W. E., Fry, A. R. 2015; 22: 526–31

  Abstract

  Ultrafast optical lasers play an essential role in exploiting the unique capabilities of recently commissioned X-ray free-electron laser facilities such as the Linac Coherent Light Source (LCLS). Pump-probe experimental techniques reveal ultrafast dynamics in atomic and molecular processes and reveal new insights in chemistry, biology, material science and high-energy-density physics. This manuscript describes the laser systems and experimental methods that enable cutting-edge optical laser/X-ray pump-probe experiments to be performed at LCLS.

  View details for PubMedID 25931064

  View details for PubMedCentralID PMC4416671

• Nonlinear THz Optics and Control in Complex Solids Hoffmann, M. C., IEEE IEEE. 2015

  View details for Web of Science ID 000370627101490

• Intense THz pulses for condensed matter physics Hoffmann, M. C., Vodopyanov, K. L. SPIE-INT SOC OPTICAL ENGINEERING. 2015

  View details for DOI 10.1117/12.2085105

  View details for Web of Science ID 000354360500012

• Ultrafast terahertz-induced response of GeSbTe phase-change materials APPLIED PHYSICS LETTERS Shu, M. J., Zalden, P., Chen, F., Weems, B., Chatzakis, I., Xiong, F., Jeyasingh, R., Hoffmann, M. C., Pop, E., Wong, H. P., Wuttig, M., Lindenberg, A. M. 2014; 104 (25)

  View details for DOI 10.1063/1.4884816

  View details for Web of Science ID 000338515900032

• THz Light Source at SLAC FACET User Facility Wu, Z., Fisher, A. S., Hoffmann, M. C., Bonetti, S., Higley, D., Durr, H., IEEE IEEE. 2014

  View details for Web of Science ID 000378889200288

• Selective THz excitation of collective modes in underdoped YBCO Dakovski, G. L., Lee, W., Turner, J. J., Hoffmann, M. C., IEEE IEEE. 2014

  View details for Web of Science ID 000369908600359

• Terahertz Nonlinear Optics in Semiconductors Turchinovich, D., Hvam, J. M., Hoffmann, M. C., IEEE IEEE. 2013

  View details for Web of Science ID 000345855300466

• Terahertz semiconductor nonlinear optics Turchinovich, D., Hvam, J. M., Hoffmann, M. C., Betz, M., Elezzabi, A. Y., Song, J. J., Tsen, K. T. SPIE-INT SOC OPTICAL ENGINEERING. 2013

  View details for DOI 10.1117/12.2000169

  View details for Web of Science ID 000322829300012

• Self-phase modulation of a single-cycle terahertz pulse by nonlinear free-carrier response in a semiconductor PHYSICAL REVIEW B Turchinovich, D., Hvam, J. M., Hoffmann, M. C. 2012; 85 (20)

  View details for DOI 10.1103/PhysRevB.85.201304

  View details for Web of Science ID 000304526800002

• THz quantum-confined Stark effect in semiconductor quantum dots Turchinovich, D., Monozon, B. S., Livshits, D. A., Rafailov, E. U., Hoffmann, M. C., Betz, M., Elezzabi, A. Y., Song, J. J., Tsen, K. T. SPIE-INT SOC OPTICAL ENGINEERING. 2012

  View details for DOI 10.1117/12.906448

  View details for Web of Science ID 000302550300002

• Nonlinear propagation of strong-field THz pulses in doped semiconductors Turchinovich, D., Hvam, J. M., Hoffmann, M. C., Betz, M., Elezzabi, A. Y., Song, J. J., Tsen, K. T. SPIE-INT SOC OPTICAL ENGINEERING. 2012

  View details for DOI 10.1117/12.906459

  View details for Web of Science ID 000302550300009

• Coherent single-cycle pulses with MV/cm field strengths from a relativistic transition radiation light source OPTICS LETTERS Hoffmann, M. C., Schulz, S., Wesch, S., Wunderlich, S., Cavalleri, A., Schmidt, B. 2011; 36 (23): 4473–75

  Abstract

  Terahertz (THz) pulses with energies up to 100 μJ and corresponding electric fields up to 1 MV/cm were generated by coherent transition radiation from 500 MeV electron bunches at the free-electron laser Freie-Elektronen-Laser in Hamburg (FLASH). The pulses were characterized in the time domain by electro-optical sampling by a synchronized femtosecond laser with jitter of less than 100 fs. High THz field strengths and quality of synchronization with an optical laser will enable observation of nonlinear THz phenomena.

  View details for PubMedID 22139213

• Intense ultrashort terahertz pulses: generation and applications JOURNAL OF PHYSICS D-APPLIED PHYSICS Hoffmann, M. C., Fueloep, J. 2011; 44 (8)

  View details for DOI 10.1088/0022-3727/44/8/083001

  View details for Web of Science ID 000287195000002

• MV/cm THz pulses from a coherent transition radiation source Hoffmann, M. C., Schulz, S., Wesch, S., Wunderlich, S., Schmidt, B., Koch, M. IEEE. 2011

  View details for Web of Science ID 000330296300156

• Ultrafast THz Saturable Absorption in Doped Semiconductors Turchinovich, D., Hoffmann, M. C., IEEE IEEE. 2011

  View details for Web of Science ID 000295612402337

• THz Electro-absorption Effect in Quantum Dots Turchinovich, D., Monozon, B. S., Livshits, D. A., Rafailov, E. U., Hoffmann, M. C., IEEE IEEE. 2011

  View details for Web of Science ID 000295612403302

• Semiconductor saturable absorbers for ultrafast terahertz signals APPLIED PHYSICS LETTERS Hoffmann, M. C., Turchinovich, D. 2010; 96 (15)

  View details for DOI 10.1063/1.3386542

  View details for Web of Science ID 000276794100010

• Observation of nonequilibrium carrier distribution in Ge, Si, and GaAs by terahertz pump-terahertz probe measurements PHYSICAL REVIEW B Hebling, J., Hoffmann, M. C., Hwang, H. Y., Yeh, K., Nelson, K. A. 2010; 81 (3)

  View details for DOI 10.1103/PhysRevB.81.035201

  View details for Web of Science ID 000274002300046

• Terahertz Kerr effect APPLIED PHYSICS LETTERS Hoffmann, M. C., Brandt, N. C., Hwang, H. Y., Yeh, K., Nelson, K. A. 2009; 95 (23)

  View details for DOI 10.1063/1.3271520

  View details for Web of Science ID 000272627700005

• Terahertz time-domain spectroscopy and imaging of artificial RNA OPTICS EXPRESS Fischer, B. M., Hoffmann, M., Helm, H., Wilk, R., Rutz, F., Kleine-Ostmann, T., Koch, M., Jepsen, P. U. 2005; 13 (14): 5205–15

  Abstract

  We use terahertz time-domain spectroscopy (THz-TDS) to measure the far-infrared dielectric function of two artificial RNA single strands, composed of polyadenylic acid (poly-A) and polycytidylic acid (poly-C). We find a significant difference in the absorption between the two types of RNA strands, and we show that we can use this difference to record images of spot arrays of the RNA strands. Under controlled conditions it is possible to use the THz image to distinguish between the two RNA strands. We discuss the requirements to sample preparation imposed by the lack of sharp spectral features in the absorption spectra.

  View details for DOI 10.1364/OPEX.13.005205

  View details for Web of Science ID 000230519100003

  View details for PubMedID 19498511