I am a condensed matter physicist with research interests in quantum materials, ultrafast optics and X-ray science. I grew up in the Stanford neighborhood where I attended Palo Alto High School. I went on to the College of Creative Studies at UCSB where i worked in the lab of David Awschalom studying semiconductor spintronics. I got my PhD in physics from the University of Colorado, Boulder, working with Dan Dessau, where we developed the first system to perform angle-resolved photoemission spectroscopy (ARPES) using a table-top laser rather than a large synchrotron facility. I moved to Lawrence Berkeley National Lab for my postdoctoral research with Joe Orenstein where we applied a wide variety of ultrafast optical techniques to study emergent properties in quantum materials and semiconductor devices. I stayed in Berkeley to work with Bob Schoenlein developing ultrafast X-ray techniques to study quantum materials. In 2014 I moved to SLAC where I am now a staff scientist in the Materials ScienceDepartment at the Linac Coherent Light Source (LCLS), the world's first X-ray free-electron laser.

Education & Certifications

  • BS, University of California, Santa Barbara, College of Creative Studies, Physics (1999)
  • PhD, University of Colorado, Boulder, Physics (2006)

All Publications

  • Liquid Heterostructures: Generation of Liquid-Liquid Interfaces in Free-Flowing Liquid Sheets. Langmuir : the ACS journal of surfaces and colloids Hoffman, D. J., Bechtel, H. A., Huyke, D. A., Santiago, J. G., DePonte, D. P., Koralek, J. D. 2022


    Chemical reactions and biological processes are frequently governed by the structure and dynamics of the interface between two liquid phases, but these interfaces are often difficult to study due to the relative abundance of the bulk liquids. Here, we demonstrate a method for generating multilayer thin film stacks of liquids, which we call liquid heterostructures. These free-flowing layered liquid sheets are produced with a microfluidic nozzle that impinges two converging jets of one liquid onto opposite sides of a third jet of another liquid. The resulting sheet consists of two layers of the first liquid enveloping an inner layer of the second liquid. Infrared microscopy, white light reflectivity, and imaging ellipsometry measurements demonstrate that the buried liquid layer has a tunable thickness and displays well-defined liquid-liquid interfaces and that this inner layer can be only tens of nanometers thick. The demonstrated multilayer liquid sheets minimize the amount of bulk liquid relative to their buried interfaces, which makes them ideal targets for spectroscopy and scattering experiments.

    View details for DOI 10.1021/acs.langmuir.2c01724

    View details for PubMedID 36220141

  • Generation and characterization of ultrathin free-flowing liquid sheets NATURE COMMUNICATIONS Koralek, J. D., Kim, J. B., Bruza, P., Curry, C. B., Chen, Z., Bechtel, H. A., Cordones, A. A., Sperling, P., Toleikis, S., Kern, J. F., Moeller, S. P., Glenzer, S. H., DePonte, D. P. 2018; 9: 1353


    The physics and chemistry of liquid solutions play a central role in science, and our understanding of life on Earth. Unfortunately, key tools for interrogating aqueous systems, such as infrared and soft X-ray spectroscopy, cannot readily be applied because of strong absorption in water. Here we use gas-dynamic forces to generate free-flowing, sub-micron, liquid sheets which are two orders of magnitude thinner than anything previously reported. Optical, infrared, and X-ray spectroscopies are used to characterize the sheets, which are found to be tunable in thickness from over 1 μm  down to less than 20 nm, which corresponds to fewer than 100 water molecules thick. At this thickness, aqueous sheets can readily transmit photons across the spectrum, leading to potentially transformative applications in infrared, X-ray, electron spectroscopies and beyond. The ultrathin sheets are stable for days in vacuum, and we demonstrate their use at free-electron laser and synchrotron light sources.

    View details for DOI 10.1038/s41467-018-03696-w

    View details for Web of Science ID 000429521200005

    View details for PubMedID 29636445

    View details for PubMedCentralID PMC5893585

  • Femtosecond structural dynamics drives the trans/cis isomerization in photoactive yellow protein SCIENCE Pande, K., Hutchison, C. M., Groenhof, G., Aquila, A., Robinson, J. S., Tenboer, J., Basu, S., Boutet, S., DePonte, D. P., Liang, M., White, T. A., Zatsepin, N. A., Yefanov, O., Morozov, D., Oberthuer, D., Gati, C., Subramanian, G., James, D., Zhao, Y., Koralek, J., Brayshaw, J., Kupitz, C., Conrad, C., Roy-Chowdhury, S., Coe, J. D., Metz, M., Xavier, P., Grant, T. D., Koglin, J. E., Ketawala, G., Fromme, R., Srajer, V., Henning, R., Spence, J. H., Ourmazd, A., Schwander, P., Weierstall, U., Frank, M., Fromme, P., Barty, A., Chapman, H. N., Moffat, K., van Thor, J. J., Schmidt, M. 2016; 352 (6286): 725–29


    A variety of organisms have evolved mechanisms to detect and respond to light, in which the response is mediated by protein structural changes after photon absorption. The initial step is often the photoisomerization of a conjugated chromophore. Isomerization occurs on ultrafast time scales and is substantially influenced by the chromophore environment. Here we identify structural changes associated with the earliest steps in the trans-to-cis isomerization of the chromophore in photoactive yellow protein. Femtosecond hard x-ray pulses emitted by the Linac Coherent Light Source were used to conduct time-resolved serial femtosecond crystallography on photoactive yellow protein microcrystals over a time range from 100 femtoseconds to 3 picoseconds to determine the structural dynamics of the photoisomerization reaction.

    View details for DOI 10.1126/science.aad5081

    View details for Web of Science ID 000375417100042

    View details for PubMedID 27151871

    View details for PubMedCentralID PMC5291079

  • Tracking Cooper Pairs in a Cuprate Superconductor by Ultrafast Angle-Resolved Photoemission SCIENCE Smallwood, C. L., Hinton, J. P., Jozwiak, C., Zhang, W., Koralek, J. D., Eisaki, H., Lee, D., Orenstein, J., Lanzara, A. 2012; 336 (6085): 1137–39


    In high-temperature superconductivity, the process that leads to the formation of Cooper pairs, the fundamental charge carriers in any superconductor, remains mysterious. We used a femtosecond laser pump pulse to perturb superconducting Bi(2)Sr(2)CaCu(2)O(8+δ) and studied subsequent dynamics using time- and angle-resolved photoemission and infrared reflectivity probes. Gap and quasiparticle population dynamics revealed marked dependencies on both excitation density and crystal momentum. Close to the d-wave nodes, the superconducting gap was sensitive to the pump intensity, and Cooper pairs recombined slowly. Far from the nodes, pumping affected the gap only weakly, and recombination processes were faster. These results demonstrate a new window into the dynamical processes that govern quasiparticle recombination and gap formation in cuprates.

    View details for DOI 10.1126/science.1217423

    View details for Web of Science ID 000304647900043

    View details for PubMedID 22654053

  • From a Single-Band Metal to a High-Temperature Superconductor via Two Thermal Phase Transitions SCIENCE He, R., Hashimoto, M., Karapetyan, H., Koralek, J. D., Hinton, J. P., Testaud, J. P., Nathan, V., Yoshida, Y., Yao, H., Tanaka, K., Meevasana, W., Moore, R. G., Lu, D. H., Mo, S., Ishikado, M., Eisaki, H., Hussain, Z., Devereaux, T. P., Kivelson, S. A., Orenstein, J., Kapitulnik, A., Shen, Z. 2011; 331 (6024): 1579-1583


    The nature of the pseudogap phase of cuprate high-temperature superconductors is a major unsolved problem in condensed matter physics. We studied the commencement of the pseudogap state at temperature T* using three different techniques (angle-resolved photoemission spectroscopy, polar Kerr effect, and time-resolved reflectivity) on the same optimally doped Bi2201 crystals. We observed the coincident, abrupt onset at T* of a particle-hole asymmetric antinodal gap in the electronic spectrum, a Kerr rotation in the reflected light polarization, and a change in the ultrafast relaxational dynamics, consistent with a phase transition. Upon further cooling, spectroscopic signatures of superconductivity begin to grow close to the superconducting transition temperature (T(c)), entangled in an energy-momentum-dependent manner with the preexisting pseudogap features, ushering in a ground state with coexisting orders.

    View details for DOI 10.1126/science.1198415

    View details for PubMedID 21436447

  • Emergence of the persistent spin helix in semiconductor quantum wells NATURE Koralek, J. D., Weber, C. P., Orenstein, J., Bernevig, B. A., Zhang, S., Mack, S., Awschalom, D. D. 2009; 458 (7238): 610–U73


    According to Noether's theorem, for every symmetry in nature there is a corresponding conservation law. For example, invariance with respect to spatial translation corresponds to conservation of momentum. In another well-known example, invariance with respect to rotation of the electron's spin, or SU(2) symmetry, leads to conservation of spin polarization. For electrons in a solid, this symmetry is ordinarily broken by spin-orbit coupling, allowing spin angular momentum to flow to orbital angular momentum. However, it has recently been predicted that SU(2) can be achieved in a two-dimensional electron gas, despite the presence of spin-orbit coupling. The corresponding conserved quantities include the amplitude and phase of a helical spin density wave termed the 'persistent spin helix'. SU(2) is realized, in principle, when the strengths of two dominant spin-orbit interactions, the Rashba (strength parameterized by alpha) and linear Dresselhaus (beta(1)) interactions, are equal. This symmetry is predicted to be robust against all forms of spin-independent scattering, including electron-electron interactions, but is broken by the cubic Dresselhaus term (beta(3)) and spin-dependent scattering. When these terms are negligible, the distance over which spin information can propagate is predicted to diverge as alpha approaches beta(1). Here we report experimental observation of the emergence of the persistent spin helix in GaAs quantum wells by independently tuning alpha and beta(1). Using transient spin-grating spectroscopy, we find a spin-lifetime enhancement of two orders of magnitude near the symmetry point. Excellent quantitative agreement with theory across a wide range of sample parameters allows us to obtain an absolute measure of all relevant spin-orbit terms, identifying beta(3) as the main SU(2)-violating term in our samples. The tunable suppression of spin relaxation demonstrated in this work is well suited for application to spintronics.

    View details for DOI 10.1038/nature07871

    View details for Web of Science ID 000264796200036

    View details for PubMedID 19340077

  • Laser based angle-resolved photoemission, the sudden approximation, and quasiparticle-like spectral peaks in Bi2Sr2CaCu2O8+delta PHYSICAL REVIEW LETTERS Koralek, J. D., Douglas, J. F., Plumb, N. C., Sun, Z., Fedorov, A. V., Murnane, M. M., Kapteyn, H. C., Cundiff, S. T., Aiura, Y., Oka, K., Eisaki, H., Dessau, D. S. 2006; 96 (1): 017005


    A new low photon energy regime of angle-resolved photoemission spectroscopy is accessed with lasers and used to study the high T(C) superconductor Bi2Sr2CaCu2O(8+delta). The low energy increases bulk sensitivity, reduces background, and improves resolution. With this we observe spectral peaks which are sharp on the scale of their binding energy--the clearest evidence yet for quasiparticles in the normal state. Crucial aspects of the data such as the dispersion, superconducting gaps, and the bosonic coupling kink are found to be robust to a possible breakdown of the sudden approximation.

    View details for PubMedID 16486502

  • Enhanced charge density wave coherence in a light-quenched, high-temperature superconductor. Science (New York, N.Y.) Wandel, S., Boschini, F., da Silva Neto, E. H., Shen, L., Na, M. X., Zohar, S., Wang, Y., Welch, S. B., Seaberg, M. H., Koralek, J. D., Dakovski, G. L., Hettel, W., Lin, M., Moeller, S. P., Schlotter, W. F., Reid, A. H., Minitti, M. P., Boyle, T., He, F., Sutarto, R., Liang, R., Bonn, D., Hardy, W., Kaindl, R. A., Hawthorn, D. G., Lee, J., Kemper, A. F., Damascelli, A., Giannetti, C., Turner, J. J., Coslovich, G. 2022; 376 (6595): 860-864


    Superconductivity and charge density waves (CDWs) are competitive, yet coexisting, orders in cuprate superconductors. To understand their microscopic interdependence, a probe capable of discerning their interaction on its natural length and time scale is necessary. We use ultrafast resonant soft x-ray scattering to track the transient evolution of CDW correlations in YBa2Cu3O6+x after the quench of superconductivity by an infrared laser pulse. We observe a nonthermal response of the CDW order characterized by a near doubling of the correlation length within 1 picosecond of the superconducting quench. Our results are consistent with a model in which the interaction between superconductivity and CDWs manifests inhomogeneously through disruption of spatial coherence, with superconductivity playing the dominant role in stabilizing CDW topological defects, such as discommensurations.

    View details for DOI 10.1126/science.abd7213

    View details for PubMedID 35587968

  • Microfluidic liquid sheets as large-area targets for high repetition XFELs. Frontiers in molecular biosciences Hoffman, D. J., Van Driel, T. B., Kroll, T., Crissman, C. J., Ryland, E. S., Nelson, K. J., Cordones, A. A., Koralek, J. D., DePonte, D. P. 2022; 9: 1048932


    The high intensity of X-ray free electron lasers (XFELs) can damage solution-phase samples on every scale, ranging from the molecular or electronic structure of a sample to the macroscopic structure of a liquid microjet. By using a large surface area liquid sheet microjet as a sample target instead of a standard cylindrical microjet, the incident X-ray spot size can be increased such that the incident intensity falls below the damage threshold. This capability is becoming particularly important for high repetition rate XFELs, where destroying a target with each pulse would require prohibitively large volumes of sample. We present here a study of microfluidic liquid sheet dimensions as a function of liquid flow rate. Sheet lengths, widths and thickness gradients are shown for three styles of nozzles fabricated from isotropically etched glass. In-vacuum operation and sample recirculation using these nozzles is demonstrated. The effects of intense XFEL pulses on the structure of a liquid sheet are also briefly examined.

    View details for DOI 10.3389/fmolb.2022.1048932

    View details for PubMedID 36567947

  • Spontaneous fluctuations in a magnetic Fe/Gd skyrmion lattice PHYSICAL REVIEW RESEARCH Seaberg, M. H., Holladay, B., Montoya, S. A., Zheng, X. Y., Lee, J. T., Reid, A. H., Koralek, J. D., Shen, L., Esposito, Coslovich, G., Walter, P., Zohar, S., Thampy, Lin, M. F., Hart, P., Nakahara, K., Streubel, R., Kevan, S. D., Fischer, P., Colocho, W., Lutman, A., Decker, F., Fullerton, E. E., Dunne, M., Roy, S., Sinha, S. K., Turner, J. J. 2021; 3 (3)
  • Observation of a highly conductive warm dense state of water with ultrafast pump-probe free-electron-laser measurements MATTER AND RADIATION AT EXTREMES Chen, Z., Na, X., Curry, C. B., Liang, S., French, M., Descamps, A., DePonte, D. P., Koralek, J. D., Kim, J. B., Lebovitz, S., Nakatsutsumi, M., Ofori-Okai, B. K., Redmer, R., Roedel, C., Schorner, M., Skruszewicz, S., Sperling, P., Toleikis, S., Mo, M. Z., Glenzer, S. H. 2021; 6 (5)

    View details for DOI 10.1063/5.0043726

    View details for Web of Science ID 000681018600001

  • The Photoactive Excited State of the B12-Based Photoreceptor CarH. The journal of physical chemistry. B Miller, N. A., Kaneshiro, A. K., Konar, A., Alonso-Mori, R., Britz, A., Deb, A., Glownia, J. M., Koralek, J. D., Mallik, L., Meadows, J. H., Michocki, L. B., van Driel, T. B., Koutmos, M., Padmanabhan, S., Elias-Arnanz, M., Kubarych, K. J., Marsh, E. N., Penner-Hahn, J. E., Sension, R. J. 2020


    We have used transient absorption spectroscopy in the UV-visible and X-ray regions to characterize the excited state of CarH, a protein photoreceptor that uses a form of B12, adenosylcobalamin (AdoCbl), to sense light. With visible excitation, a nanosecond-lifetime photoactive excited state is formed with unit quantum yield. The time-resolved X-ray absorption near edge structure difference spectrum of this state demonstrates that the excited state of AdoCbl in CarH undergoes only modest structural expansion around the central cobalt, a behavior similar to that observed for methylcobalamin rather than for AdoCbl free in solution. We propose a new mechanism for CarH photoreactivity involving formation of a triplet excited state. This allows the sensor to operate with high quantum efficiency and without formation of potentially dangerous side products. By stabilizing the excited electronic state, CarH controls reactivity of AdoCbl and enables slow reactions that yield nonreactive products and bypass bond homolysis and reactive radical species formation.

    View details for DOI 10.1021/acs.jpcb.0c09428

    View details for PubMedID 33174757

  • Observation of Seeded Mn K beta Stimulated X-Ray Emission Using Two-Color X-Ray Free-Electron Laser Pulses PHYSICAL REVIEW LETTERS Kroll, T., Weninger, C., Fuller, F. D., Guetg, M. W., Benediktovitch, A., Zhang, Y., Marinelli, A., Alonso-Mori, R., Aquila, A., Liang, M., Koglin, J. E., Koralek, J., Sokaras, D., Zhu, D., Kern, J., Yano, J., Yachandra, V. K., Rohringer, N., Lutman, A., Bergmann, U. 2020; 125 (3)
  • Skyrmion fluctuations at a first-order phase transition boundary APPLIED PHYSICS LETTERS Esposito, Zheng, X. Y., Seaberg, M. H., Montoya, S. A., Holladay, B., Reid, A. H., Streubel, R., Lee, J. T., Shen, L., Koralek, J. D., Coslovich, G., Walter, P., Zohar, S., Thampy, Lin, M. F., Hart, P., Nakahara, K., Fischer, P., Colocho, W., Lutman, A., Decker, F., Sinha, S. K., Fullerton, E. E., Kevan, S. D., Roy, S., Dunne, M., Turner, J. J. 2020; 116 (18)

    View details for DOI 10.1063/5.0004879

    View details for Web of Science ID 000532284300001

  • Antivitamins B12 in a Microdrop: The Excited-State Structure of a Precious Sample Using Transient Polarized X-ray Absorption Near-Edge Structure. The journal of physical chemistry letters Miller, N. A., Michocki, L. B., Alonso-Mori, R., Britz, A., Deb, A., DePonte, D. P., Glownia, J. M., Kaneshiro, A. K., Kieninger, C., Koralek, J., Meadows, J. H., van Driel, T. B., Krautler, B., Kubarych, K. J., Penner-Hahn, J. E., Sension, R. J. 2019: 5484–89


    Polarized transient X-ray absorption near-edge structure (XANES) was used to probe the excited-state structure of a photostable B12 antivitamin (Cobeta-2-(2,4-difluorophenyl)-ethynylcobalamin, F2PhEtyCbl). A drop-on-demand delivery system synchronized to the LCLS X-ray free electron laser pulses was implemented and used to measure the XANES difference spectrum 12 ps following excitation, exposing only 45 muL of sample. Unlike cyanocobalamin (CNCbl), where the Co-C bond expands 15-20%, the excited state of F2PhEtyCbl is characterized by little change in the Co-C bond, suggesting that the acetylide linkage raises the barrier for expansion of the Co-C bond. In contrast, the lower axial Co-NDMB bond is elongated in the excited state of F2PhEtyCbl by ca. 10% or more, comparable to the 10% elongation observed for Co-NDMB in CNCbl.

    View details for DOI 10.1021/acs.jpclett.9b02202

    View details for PubMedID 31483136

  • Author Correction: Generation and characterization of ultrathin free-flowing liquid sheets. Nature communications Koralek, J. D., Kim, J. B., Bruza, P., Curry, C. B., Chen, Z., Bechtel, H. A., Cordones, A. A., Sperling, P., Toleikis, S., Kern, J. F., Moeller, S. P., Glenzer, S. H., DePonte, D. P. 2019; 10 (1): 1615


    The original version of this Article contained an error in Eq. (1). This has been corrected in both the PDF and HTML versions of the Article.

    View details for DOI 10.1038/s41467-019-09457-7

    View details for PubMedID 30944301

  • Author Correction: Generation and characterization of ultrathin free-flowing liquid sheets. Nature communications Koralek, J. D., Kim, J. B., Bruza, P., Curry, C. B., Chen, Z., Bechtel, H. A., Cordones, A. A., Sperling, P., Toleikis, S., Kern, J. F., Moeller, S. P., Glenzer, S. H., DePonte, D. P. 2018; 9 (1): 2860


    The original version of this article omitted the following from the Acknowledgements:'P.B. was funded by the ELI Extreme Light Infrastructure Phase 2 (CZ.02.1.01/0.0/0.0/15008/0000162) from the European Regional Development Fund and the EUCALL project funded from the EU Horizon 2020 research and innovation programme under grant agreement No 654220,' which replaces the previous 'P.B. was funded by the ELI Extreme Light Infrastructure Phase 2 (CZ.02.1.01/0.0/0.0/15008/0000162) from the European Regional Development Fund.'This has been corrected in both the PDF and HTML versions of the article.

    View details for DOI 10.1038/s41467-018-05365-4

    View details for PubMedID 30018291

  • Coherent X-rays reveal the influence of cage effects on ultrafast water dynamics NATURE COMMUNICATIONS Perakis, F., Camisasca, G., Lane, T. J., Spah, A., Wikfeldt, K., Sellberg, J. A., Lehmkuehler, F., Pathak, H., Kim, K., Amann-Winkel, K., Schreck, S., Song, S., Sato, T., Sikorski, M., Eilert, A., McQueen, T., Ogasawara, H., Nordlund, D., Roseker, W., Koralek, J., Nelson, S., Hart, P., Alonso-Mori, R., Feng, Y., Zhu, D., Robert, A., Gruebel, G., Pettersson, L. M., Nilsson, A. 2018; 9: 1917


    The dynamics of liquid water feature a variety of time scales, ranging from extremely fast ballistic-like thermal motion, to slower molecular diffusion and hydrogen-bond rearrangements. Here, we utilize coherent X-ray pulses to investigate the sub-100 fs equilibrium dynamics of water from ambient conditions down to supercooled temperatures. This novel approach utilizes the inherent capability of X-ray speckle visibility spectroscopy to measure equilibrium intermolecular dynamics with lengthscale selectivity, by measuring oxygen motion in momentum space. The observed decay of the speckle contrast at the first diffraction peak, which reflects tetrahedral coordination, is attributed to motion on a molecular scale within the first 120 fs. Through comparison with molecular dynamics simulations, we conclude that the slowing down upon cooling from 328 K down to 253 K is not due to simple thermal ballistic-like motion, but that cage effects play an important role even on timescales over 25 fs due to hydrogen-bonding.

    View details for PubMedID 29765052

  • Stimulated X-Ray Emission Spectroscopy in Transition Metal Complexes PHYSICAL REVIEW LETTERS Kroll, T., Weninger, C., Alonso-Mori, R., Sokaras, D., Zhu, D., Mercadier, L., Majety, V. P., Marinelli, A., Lutman, A., Guetg, M. W., Decker, F., Boutet, S., Aquila, A., Koglin, J., Koralek, J., DePonte, D. P., Kern, J., Fuller, F. D., Pastor, E., Fransson, T., Zhang, Y., Yano, J., Yachandra, V. K., Rohringer, N., Bergmann, U. 2018; 120 (13): 133203


    We report the observation and analysis of the gain curve of amplified Kα x-ray emission from solutions of Mn(II) and Mn(VII) complexes using an x-ray free electron laser to create the 1s core-hole population inversion. We find spectra at amplification levels extending over 4 orders of magnitude until saturation. We observe bandwidths below the Mn 1s core-hole lifetime broadening in the onset of the stimulated emission. In the exponential amplification regime the resolution corrected spectral width of ∼1.7  eV FWHM is constant over 3 orders of magnitude, pointing to the buildup of transform limited pulses of ∼1  fs duration. Driving the amplification into saturation leads to broadening and a shift of the line. Importantly, the chemical sensitivity of the stimulated x-ray emission to the Mn oxidation state is preserved at power densities of ∼10^{20}  W/cm^{2} for the incoming x-ray pulses. Differences in signal sensitivity and spectral information compared to conventional (spontaneous) x-ray emission spectroscopy are discussed. Our findings build a baseline for nonlinear x-ray spectroscopy for a wide range of transition metal complexes in inorganic chemistry, catalysis, and materials science.

    View details for DOI 10.1103/PhysRevLett.120.133203

    View details for Web of Science ID 000428394800008

    View details for PubMedID 29694162

  • Nonlinear Ultrafast Spin Scattering in the Skyrmion Phase of Cu2OSeO3 PHYSICAL REVIEW LETTERS Langner, M. C., Roy, S., Huang, S. W., Koralek, J. D., Chuang, Y., Dakovski, G. L., Turner, J. J., Robinson, J. S., Coffee, R. N., Minitti, M. P., Seki, S., Tokura, Y., Schoenlein, R. W. 2017; 119 (10): 107204


    Ultrafast x-ray scattering studies of the topological Skyrmion phase in Cu_{2}OSeO_{3} show the dynamics to be strongly dependent on the excitation energy and fluence. At high photon energies, where the electron-spin scattering cross section is relatively high, the excitation of the topological Skyrmion phase shows a nonlinear dependence on the excitation fluence, in contrast to the excitation of the conical phase which is linearly dependent on the excitation fluence. The excitation of the Skyrmion order parameter is nonlinear in the magnetic excitation resulting from scattering during electron-hole recombination, indicating different dominant scattering processes in the conical and Skyrmion phases.

    View details for DOI 10.1103/PhysRevLett.119.107204

    View details for Web of Science ID 000409560100006

    View details for PubMedID 28949160

  • Nanosecond X-Ray Photon Correlation Spectroscopy on Magnetic Skyrmions PHYSICAL REVIEW LETTERS Seaberg, M. H., Holladay, B., Lee, J. T., Sikorski, M., Reid, A. H., Montoya, S. A., Dakovski, G. L., Koralek, J. D., Coslovich, G., Moeller, S., Schlotter, W. F., Streubel, R., Kevan, S. D., Fischer, P., Fullerton, E. E., Turner, J. L., Decker, F., Sinha, S. K., Roy, S., Turner, J. J. 2017; 119 (6): 067403


    We report an x-ray photon correlation spectroscopy method that exploits the recent development of the two-pulse mode at the Linac Coherent Light Source. By using coherent resonant x-ray magnetic scattering, we studied spontaneous fluctuations on nanosecond time scales in thin films of multilayered Fe/Gd that exhibit ordered stripe and Skyrmion lattice phases. The correlation time of the fluctuations was found to differ between the Skyrmion phase and near the stripe-Skyrmion boundary. This technique will enable a significant new area of research on the study of equilibrium fluctuations in condensed matter.

    View details for DOI 10.1103/PhysRevLett.119.067403

    View details for Web of Science ID 000407273700005

    View details for PubMedID 28949638

  • Polarized XANES Monitors Femtosecond Structural Evolution of Photoexcited Vitamin B-12 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Miller, N. A., Deb, A., Alonso-Mori, R., Garabato, B. D., Glownia, J. M., Kiefer, L. M., Koralek, J., Sikorski, M., Spears, K. G., Wiley, T. E., Zhu, D., Kozlowski, P. M., Kubarych, K. J., Penner-Hahn, J. E., Sension, R. J. 2017; 139 (5): 1894–99


    Ultrafast, polarization-selective time-resolved X-ray absorption near-edge structure (XANES) was used to characterize the photochemistry of vitamin B12, cyanocobalamin (CNCbl), in solution. Cobalamins are important biological cofactors involved in methyl transfer, radical rearrangement, and light-activated gene regulation, while also holding promise as light-activated agents for spatiotemporal controlled delivery of therapeutics. We introduce polarized femtosecond XANES, combined with UV-visible spectroscopy, to reveal sequential structural evolution of CNCbl in the excited electronic state. Femtosecond polarized XANES provides the crucial structural dynamics link between computed potential energy surfaces and optical transient absorption spectroscopy. Polarization selectivity can be used to uniquely identify electronic contributions and structural changes, even in isotropic samples when well-defined electronic transitions are excited. Our XANES measurements reveal that the structural changes upon photoexcitation occur mainly in the axial direction, where elongation of the axial Co-CN bond and Co-NIm bond on a 110 fs time scale is followed by corrin ring relaxation on a 260 fs time scale. These observations expose features of the potential energy surfaces controlling cobalamin reactivity and deactivation.

    View details for DOI 10.1021/jacs.6b11295

    View details for Web of Science ID 000393848400038

    View details for PubMedID 28135083

  • The room temperature crystal structure of a bacterial phytochrome determined by serial femtosecond crystallography SCIENTIFIC REPORTS Edlund, P., Takala, H., Claesson, E., Henry, L., Dods, R., Lehtivuori, H., Panman, M., Pande, K., White, T., Nakane, T., Berntsson, O., Gustavsson, E., Bath, P., Modi, V., Roy-Chowdhury, S., Zook, J., Berntsen, P., Pandey, S., Poudyal, I., Tenboer, J., Kupitz, C., Barty, A., Fromme, P., Koralek, J. D., Tanaka, T., Spence, J., Liang, M., Hunter, M. S., Boutet, S., Nango, E., Moffat, K., Groenhof, G., Ihalainen, J., Stojkovic, E. A., Schmidt, M., Westenhoff, S. 2016; 6: 35279


    Phytochromes are a family of photoreceptors that control light responses of plants, fungi and bacteria. A sequence of structural changes, which is not yet fully understood, leads to activation of an output domain. Time-resolved serial femtosecond crystallography (SFX) can potentially shine light on these conformational changes. Here we report the room temperature crystal structure of the chromophore-binding domains of the Deinococcus radiodurans phytochrome at 2.1 Å resolution. The structure was obtained by serial femtosecond X-ray crystallography from microcrystals at an X-ray free electron laser. We find overall good agreement compared to a crystal structure at 1.35 Å resolution derived from conventional crystallography at cryogenic temperatures, which we also report here. The thioether linkage between chromophore and protein is subject to positional ambiguity at the synchrotron, but is fully resolved with SFX. The study paves the way for time-resolved structural investigations of the phytochrome photocycle with time-resolved SFX.

    View details for DOI 10.1038/srep35279

    View details for Web of Science ID 000386145700001

    View details for PubMedID 27756898

    View details for PubMedCentralID PMC5069500

  • The rate of quasiparticle recombination probes the onset of coherence in cuprate superconductors SCIENTIFIC REPORTS Hinton, J. P., Thewalt, E., Alpichshev, Z., Mahmood, F., Koralek, J. D., Chan, M. K., Veit, M. J., Dorow, C. J., Barisic, N., Kemper, A. F., Bonn, D. A., Hardy, W. N., Liang, R., Gedik, N., Greven, M., Lanzara, A., Orenstein, J. 2016; 6: 23610


    In the underdoped copper-oxides, high-temperature superconductivity condenses from a nonconventional metallic "pseudogap" phase that exhibits a variety of non-Fermi liquid properties. Recently, it has become clear that a charge density wave (CDW) phase exists within the pseudogap regime. This CDW coexists and competes with superconductivity (SC) below the transition temperature Tc, suggesting that these two orders are intimately related. Here we show that the condensation of the superfluid from this unconventional precursor is reflected in deviations from the predictions of BSC theory regarding the recombination rate of quasiparticles. We report a detailed investigation of the quasiparticle (QP) recombination lifetime, τqp, as a function of temperature and magnetic field in underdoped HgBa2CuO(4+δ) (Hg-1201) and YBa2Cu3O(6+x) (YBCO) single crystals by ultrafast time-resolved reflectivity. We find that τqp(T) exhibits a local maximum in a small temperature window near Tc that is prominent in underdoped samples with coexisting charge order and vanishes with application of a small magnetic field. We explain this unusual, non-BCS behavior by positing that Tc marks a transition from phase-fluctuating SC/CDW composite order above to a SC/CDW condensate below. Our results suggest that the superfluid in underdoped cuprates is a condensate of coherently-mixed particle-particle and particle-hole pairs.

    View details for DOI 10.1038/srep23610

    View details for Web of Science ID 000373964900001

    View details for PubMedID 27071712

    View details for PubMedCentralID PMC4829850

  • Photoexcited states of the harmonic honeycomb iridate gamma-Li2IrO3 PHYSICAL REVIEW B Hinton, J. P., Patankar, S., Thewalt, E., Ruiz, A., Lopez, G., Breznay, N., Vishwanath, A., Analytis, J., Orenstein, J., Koralek, J. D., Kimchi, I. 2015; 92 (11)
  • New collective mode in YBa2Cu3O6+x observed by time-domain reflectometry PHYSICAL REVIEW B Hinton, J. P., Koralek, J. D., Lu, Y. M., Vishwanath, A., Orenstein, J., Bonn, D. A., Hardy, W. N., Liang, R. 2013; 88 (6)
  • Time-Resolved Optical Reflectivity of the Electron-Doped Nd2-xCexCuO4+delta Cuprate Superconductor: Evidence for an Interplay between Competing Orders PHYSICAL REVIEW LETTERS Hinton, J. P., Koralek, J. D., Yu, G., Motoyama, E. M., Lu, Y. M., Vishwanath, A., Greven, M., Orenstein, J. 2013; 110 (21)


    We use pump-probe spectroscopy to measure the photoinduced reflectivity ΔR of the electron-doped cuprate superconductor Nd(2-x)Ce(x)CuO(4+δ) at a value of x near optimal doping, as a function of time, temperature, and laser fluence. We observe the onset of a negative ΔR signal at T(*)≈75 K, above the superconducting transition temperature, T(c), of 23 K. The relatively slow decay of ΔR, compared to the analogous signal in hole doped compounds, allows us to resolve time-temperature scaling consistent with critical fluctuations. A positive ΔR signal onsets at T(c) that we associate with superconducting order. We find that the two signals are strongly coupled below T(c), in a manner that suggests a repulsive interaction between superconductivity and another fluctuating order.

    View details for DOI 10.1103/PhysRevLett.110.217002

    View details for Web of Science ID 000319278400018

    View details for PubMedID 23745913

  • Doppler velocimetry of spin and charge currents in the 2D Fermi gas Koralek, J. D., Yang, L., Tibbetts, D. R., Reno, J. L., Lilly, M. P., Orenstein, J., Chergui, M., Taylor, A., Cundiff, S., DeVivieRiedle, R., Yamagouchi, K. E D P SCIENCES. 2013
  • Coherent Propagation of Spin Helices in a Quantum-Well Confined Electron Gas PHYSICAL REVIEW LETTERS Yang, L., Koralek, J. D., Orenstein, J., Tibbetts, D. R., Reno, J. L., Lilly, M. P. 2012; 109 (24): 246603


    We use phase-resolved transient grating spectroscopy to measure the propagation of spin helices in a high mobility n-GaAs/AlGaAs quantum well with an applied in-plane electric field. At relatively low fields helical modes crossover from overdamped excitations where the spin-precession period exceeds the spin lifetime, to a regime of coherent propagation where several spin-precession periods can be observed. We demonstrate that the envelope of a spin polarization packet reaches a current-driven velocity of 10(7) cm s(-1) in an applied field of 70 V cm(-1).

    View details for DOI 10.1103/PhysRevLett.109.246603

    View details for Web of Science ID 000312299500008

    View details for PubMedID 23368357

  • Observation of Coherent Helimagnons and Gilbert Damping in an Itinerant Magnet PHYSICAL REVIEW LETTERS Koralek, J. D., Meier, D., Hinton, J. P., Bauer, A., Parameswaran, S. A., Vishwanath, A., Ramesh, R., Schoenlein, R. W., Pfleiderer, C., Orenstein, J. 2012; 109 (24): 247204


    We study the magnetic excitations of itinerant helimagnets by applying time-resolved optical spectroscopy to Fe(0.8)Co(0.2)Si. Optically excited oscillations of the magnetization in the helical state are found to disperse to lower frequency as the applied magnetic field is increased; the fingerprint of collective modes unique to helimagnets, known as helimagnons. The use of time-resolved spectroscopy allows us to address the fundamental magnetic relaxation processes by directly measuring the Gilbert damping, revealing the versatility of spin dynamics in chiral magnets.

    View details for DOI 10.1103/PhysRevLett.109.247204

    View details for Web of Science ID 000312299500010

    View details for PubMedID 23368372

  • Doppler velocimetry of spin propagation in a two-dimensional electron gas NATURE PHYSICS Yang, L., Koralek, J. D., Orenstein, J., Tibbetts, D. R., Reno, J. L., Lilly, M. P. 2012; 8 (2): 153–57

    View details for DOI 10.1038/NPHYS2157

    View details for Web of Science ID 000300403700021

  • Measurement of Electron-Hole Friction in an n-Doped GaAs/AlGaAs Quantum Well Using Optical Transient Grating Spectroscopy PHYSICAL REVIEW LETTERS Yang, L., Koralek, J. D., Orenstein, J., Tibbetts, D. R., Reno, J. L., Lilly, M. P. 2011; 106 (24): 247401


    We use phase-resolved transient grating spectroscopy to measure the drift and diffusion of electron-hole density waves in a semiconductor quantum well. The unique aspects of this optical probe allow us to determine the frictional force between a two-dimensional Fermi liquid of electrons and a dilute gas of holes. Knowledge of electron-hole friction enables prediction of ambipolar dynamics in high-mobility electron systems.

    View details for DOI 10.1103/PhysRevLett.106.247401

    View details for Web of Science ID 000291608700007

    View details for PubMedID 21770596

  • Low-Energy (< 10 meV) Feature in the Nodal Electron Self-Energy and Strong Temperature Dependence of the Fermi Velocity in Bi2Sr2CaCu2O8+delta PHYSICAL REVIEW LETTERS Plumb, N. C., Reber, T. J., Koralek, J. D., Sun, Z., Douglas, J. F., Aiura, Y., Oka, K., Eisaki, H., Dessau, D. S. 2010; 105 (4): 046402


    Using low photon energy angle-resolved photoemission, we study the low-energy dispersion along the nodal (π,π) direction in Bi{2}Sr{2}CaCu{2}O{8+δ} as a function of temperature. Less than 10 meV below the Fermi energy, the high-resolution data reveal a novel "kinklike" feature in the electron self-energy that is distinct from the larger well-known kink roughly 70 meV below E{F}. This new kink is strongest below the superconducting critical temperature and weakens substantially at higher temperatures. A corollary of this finding is that the Fermi velocity v{F}, as measured in this low-energy range, varies rapidly with temperature-increasing by almost 30% from 70 to 110 K. The behavior of v{F}(T) appears to shift as a function of doping, suggesting a departure from simple "universality" in the nodal Fermi velocity of cuprates.

    View details for PubMedID 20867869

  • Accurate theoretical fits to laser-excited photoemission spectra in the normal phase of high-temperature superconductors NATURE PHYSICS Casey, P. A., Koralek, J. D., Plumb, N. C., Dessau, D. S., Anderson, P. W. 2008; 4 (3): 210–12

    View details for DOI 10.1038/nphys833

    View details for Web of Science ID 000254559900013

  • Experimental setup for low-energy laser-based angle resolved photoemission spectroscopy REVIEW OF SCIENTIFIC INSTRUMENTS Koralek, J. D., Douglas, J. F., Plumb, N. C., Griffith, J. D., Cundiff, S. T., Kapteyn, H. C., Murnane, M. M., Dessau, D. S. 2007; 78 (5): 053905


    A laser-based angle resolved photoemission (ARPES) system utilizing 6 eV photons from the fourth harmonic of a mode-locked Ti:sapphire oscillator is described. This light source greatly increases the momentum resolution and photoelectron count rate, while reducing extrinsic background and surface sensitivity relative to higher energy light sources. In this review, the optical system is described, and special experimental considerations for low-energy ARPES are discussed. The calibration of the hemispherical electron analyzer for good low-energy angle-mode performance is also described. Finally, data from the heavily studied high T(c) superconductor Bi(2)Sr(2)CaCu(2)O(8+delta) (Bi2212) is compared to the results from higher photon energies.

    View details for PubMedID 17552839

  • Lasers emerge as a tool for the direct study of electrons in solids PHOTONICS SPECTRA Koralek, J. D., Dessau, D. S. 2006; 40 (6): 72-+
  • Mass-renormalized electronic excitations at (pi,0) in the superconducting state of Bi2Sr2CaCu2O8+delta PHYSICAL REVIEW B Gromko, A. D., Fedorov, A. V., Chuang, Y. D., Koralek, J. D., Aiura, Y., Yamaguchi, Y., Oka, K., Ando, Y., Dessau, D. S. 2003; 68 (17)