Paulina Majchrzak

All Publications

• Direct Visualization of Gate-Tunable Flat Bands in Twisted Double Bilayer Graphene. Physical review letters Sasmal, S., Muzzio, R., Khalifa, A., Majchrzak, P., Jones, A. J., Kao, I. H., Watanabe, K., Taniguchi, T., Singh, S., Rotenberg, E., Bostwick, A., Jozwiak, C., Ulstrup, S., Chatterjee, S., Katoch, J. 2026; 137 (1): 016402

  Abstract

  The symmetry-broken correlated states in twisted double bilayer graphene (TDBG) can be tuned via several external knobs, including twist angle, displacement field, and carrier density. However, a direct, momentum-resolved characterization of how these parameters reshape the flat-band structure remains limited. In this Letter, we employ microfocused angle-resolved photoemission spectroscopy to investigate the flat-band dispersion of TDBG at a twist angle of 1.6°, systematically varying the displacement field and carrier density via electrostatic gating. We directly observe multiple flat moiré minibands near charge neutrality, including a flat remote valence band residing below the low-energy flat-band manifold. Furthermore, the dominant Coulomb repulsive energy over the flat-band bandwidth suggests favorable conditions for the emergence of interaction-driven correlated phenomena in TDBG. These findings establish that the formation and evolution of flat bands in TDBG arises from the interplay between the electron filling and the displacement field.

  View details for DOI 10.1103/3vg5-vkzy

  View details for PubMedID 42489208

• Direct Visualization of Gate-Tunable Flat Bands in Twisted Double Bilayer Graphene PHYSICAL REVIEW LETTERS Sasmal, S., Muzzio, R., Khalifa, A., Majchrzak, P., Jones, A. J. H., Kao, I., Watanabe, K., Taniguchi, T., Singh, S., Rotenberg, E., Bostwick, A., Jozwiak, C., Ulstrup, S., Chatterjee, S., Katoch, J. 2026; 137 (1)

  View details for DOI 10.1103/3vg5-vkzy

  View details for Web of Science ID 001818189000004

• Clustering-enhanced time-and angle-resolved photoemission study of LaTe3: Absence of a photoinduced secondary charge density wave in the electronic structure PHYSICAL REVIEW B Siemann, G., Curcio, D., Mortensen, A. S., Sanders, C. E., Zhang, Y., Rigden, J., Majchrzak, P., Biswas, D., Springate, E., Singha, R., Schoop, L. M., Hofmann, P. 2026; 113 (7)

  View details for DOI 10.1103/81xm-bzdy

  View details for Web of Science ID 001697982700002

• Line shapes in time- and angle-resolved photoemission spectroscopy explored by machine learning ELECTRONIC STRUCTURE Meyer, T. C., Siemann, G., Majchrzak, P., Seyller, T., Rigden, J., Zhang, Y., Springate, E., Sanders, C., Hofmann, P. 2025; 7 (4)

  View details for DOI 10.1088/2516-1075/ae1e4a

  View details for Web of Science ID 001619324600001

• Nonmonotonic Band Flattening near the Magic Angle of Twisted Bilayer MoTe2 PHYSICAL REVIEW X Deng, Y., Holtzmann, W., Zhu, Z., Zaklama, T., Majchrzak, P., Taniguchi, T., Watanabe, K., Hashimoto, M., Lu, D., Jozwiak, C., Bostwick, A., Rotenberg, E., Fu, L., Devereaux, T. P., Xu, X., Shen, Z. 2025; 15 (4)

  View details for DOI 10.1103/q11l-9jy1

  View details for Web of Science ID 001680508400001

• Macroscopic Uniform 2D Moiré Superlattices with Controllable Angles. Journal of the American Chemical Society Zaborski, G., Majchrzak, P. E., Lai, S., Johnson, A. C., Li, Q., Saunders, A. P., Zhu, Z., Deng, Y., Lu, D., Hashimoto, M., Shen, Z. X., Liu, F. 2025

  Abstract

  Moiré superlattices, engineered through precise stacking of van der Waals (vdW) layers, hold immense promise for exploring strongly correlated and topological phenomena. However, these applications have been held back by the common preparation method: tear-and-stack of Scotch tape exfoliated monolayers, which suffer from low efficiency and reproducibility, twist angle inhomogeneity, interfacial contamination, and micrometer sizes. Here, we report an effective strategy to construct highly consistent mixed-dimensional and twisted bilayer vdW moiré structures with high production throughput, near-unity yield, pristine interfaces, precisely controlled twist angles, and macroscopic scale (up to centimeters) with enhanced thermal stability. We demonstrate the versatility across various vdW materials, including transition metal dichalcogenides, graphene, and hBN. The expansive size and high quality of moiré structures enable reciprocal-space high-resolution mapping of the superlattices and back-folded moiré mini band structures with low energy electron diffraction (LEED) and angle-resolved photoemission spectroscopy (ARPES). In particular, we identify the backfolded bands at the K point of twisted transition metal dichalcogenide moiré structures. This technique will have broad applications in both fundamental studies and the mass production of twistronic devices.

  View details for DOI 10.1021/jacs.5c09131

  View details for PubMedID 41060287

• Resonantly enhanced photoemission from topological surface states in MnBi6Te10. Journal of physics. Condensed matter : an Institute of Physics journal Majchrzak, P. E., Jones, A., Volckaert, K., Pan, X. C., Hofmann, P., Chen, Y. P., Miwa, J. A., Ulstrup, S. 2025

  Abstract

  The dispersion of topological surface bands in MnBi2Te4-based magnetic topological insulator heterostructures is strongly affected by band hybridization and is spatially inhomogeneous due to varying surface layer terminations on microscopic length scales. Here, we apply micro-focused angle-resolved photoemission spectroscopy with tunable photon energy from 18 to 30 eV to distinguish bulk valence and conduction bands from surface bands on the three surface terminations of MnBi6Te10. We observe a strong enhancement of photoemission intensity from the topological surface bands at the Bi O4absorption edge, which is exploited to visualize a gapless Dirac cone on the MnBi2Te4-terminated surface and varying degrees of hybridization effects in the surface bands on the two distinct Bi2Te3-terminated surfaces.

  View details for DOI 10.1088/1361-648X/ae025b

  View details for PubMedID 40897359

• Quasiparticle Gap Renormalization Driven by Internal and External Screening in a WS2 Device PHYSICAL REVIEW LETTERS Sahoo, C., Veld, Y., Jones, A. J. H., Jiang, Z., Lupi, G., Majchrzak, P. E., Hsieh, K., Watanabe, K., Taniguchi, T., Hofmann, P., Miwa, J. A., Chen, Y. P., Rosner, M., Ulstrup, S. 2025; 135 (5): 056401

  Abstract

  The electronic band gap of a two-dimensional semiconductor within a device architecture is sensitive to variations in screening properties of adjacent materials in the device and to gate-controlled doping. Here, we employ microfocused angle-resolved photoemission spectroscopy to separate band gap renormalization effects stemming from environmental screening and electron doping during in situ gating of a single-layer WS_{2} device. The WS_{2} is supported on hexagonal boron nitride and contains a section that is exposed to vacuum and another section that is encapsulated by a graphene contact. We directly observe the doping-induced semiconductor-metal transition and band gap renormalization in the two sections of WS_{2}. Surprisingly, a larger band gap renormalization is observed in the vacuum-exposed section than in the graphene-encapsulated-and thus ostensibly better screened-section of the WS_{2}. Using GW calculations, we determine that intrinsic screening due to stronger doping in vacuum-exposed WS_{2} exceeds the external environmental screening in graphene-encapsulated WS_{2}.

  View details for DOI 10.1103/yllv-5zx7

  View details for Web of Science ID 001541480800007

  View details for PubMedID 40824778

• A spatial- and angle-resolved photoemission spectroscopy beamline based on capillary optics at ASTRID2 REVIEW OF SCIENTIFIC INSTRUMENTS Jones, A. J. H., Majchrzak, P., Volckaert, K., Biswas, D., Andersen, J., Hoffmann, S. V., Jones, N. C., Jiang, Z., Chen, Y. P., Jensen, M., Stenshoj, R., Bianchi, M., Hofmann, P., Ulstrup, S., Miwa, J. A. 2025; 96 (2)

  Abstract

  Angle-resolved photoemission spectroscopy (ARPES) with spatial resolution is emerging as a powerful investigative tool for the study of operational mesoscale devices and quantum materials. Here, we introduce AU-SGM4, an extreme ultraviolet beamline based at the ASTRID2 synchrotron, which is designed around an achromatic elliptical capillary optic that focuses the synchrotron light down to a lateral beam spot size of 4 μm. The beamline offers a low photon energy range of 12-150 eV, ideal for probing detailed energy- and momentum-resolved electronic structures of materials. We utilize a custom-made piezoelectric motor system with 11 degrees of freedom for precisely moving the sample and capillary optic. We demonstrate exceptional stability in beam positioning on samples across the entire available photon energy range. To showcase the capabilities of the AU-SGM4 beamline, we present simultaneous ARPES measurements and in situ gating of a graphene device and probe the nominally inaccessible microscopic-sized domains of MnBi6Te10 to obtain the energy- and momentum-dependent dispersion for each domain.

  View details for DOI 10.1063/5.0240744

  View details for Web of Science ID 001469478000002

  View details for PubMedID 40019339

• Machine-learning approach to understanding ultrafast carrier dynamics in the three-dimensional Brillouin zone of PtBi₂ PHYSICAL REVIEW RESEARCH Majchrzak, P., Sanders, C., Zhang, Y., Kuibarov, A., Suvorov, O., Springate, E., Kovalchuk, I., Aswartham, S., Shipunov, G., Buechner, B., Yaresko, A., Borisenko, S., Hofmann, P. 2025; 7 (1)

  View details for DOI 10.1103/PhysRevResearch.7.013025

  View details for Web of Science ID 001415731200001

• Attosecond emission delay from atoms and molecules using multi-dimensional XUV interferometry NEW JOURNAL OF PHYSICS Wyatt, A. S., Lloyd, D. T., Chapman, R. T., Thornton, C., Majchrzak, P., Jones, A. J. H., Springate, E., O'Keeffe, K. 2024; 26 (11)

  View details for DOI 10.1088/1367-2630/ad8f5b

  View details for Web of Science ID 001362373000001

• Access to the full three-dimensional Brillouin zone with time resolution, using a new tool for pump-probe angle-resolved photoemission spectroscopy. The Review of scientific instruments Majchrzak, P., Zhang, Y., Kuibarov, A., Chapman, R., Wyatt, A., Springate, E., Borisenko, S., Buchner, B., Hofmann, P., Sanders, C. E. 2024; 95 (6)

  Abstract

  Here, we report the first time- and angle-resolved photoemission spectroscopy (TR-ARPES) with the new Fermiologics "FeSuMa" analyzer. The new experimental setup has been commissioned at the Artemis laboratory of the UK Central Laser Facility. We explain here some of the advantages of the FeSuMa for TR-ARPES and discuss how its capabilities relate to those of hemispherical analyzers and momentum microscopes. We have integrated the FeSuMa into an optimized pump-probe beamline that permits photon-energy (i.e., kz)-dependent scanning, using probe energies generated from high harmonics in a gas jet. The advantages of using the FeSuMa in this situation include the possibility of taking advantage of its "fisheye" mode of operation.

  View details for DOI 10.1063/5.0179752

  View details for PubMedID 38829212

• Programming twist angle and strain profiles in 2D materials SCIENCE Kapfer, M., Jessen, B. S., Eisele, M. E., Fu, M., Danielsen, D. R., Darlington, T. P., Moore, S. L., Finney, N. R., Marchese, A., Hsieh, V., Majchrzak, P., Jiang, Z., Biswas, D., Dudin, P., Avila, J., Watanabe, K., Taniguchi, T., Ulstrup, S., Boggild, P., Schuck, P. J., Basov, D. N., Hone, J., Dean, C. R. 2023; 381 (6658): 677-681

  View details for DOI 10.1126/science.ade9995

  View details for Web of Science ID 001167286600031

• Direct Visualization of Subnanometer Variations in the Excitonic Spectra of 2D/3D Semiconductor/Metal Heterostructures NANO LETTERS Reidy, K., Majchrzak, P., Haas, B., Thomsen, J., Konecna, A., Park, E., Klein, J., Jones, A. J. H., Volckaert, K., Biswas, D., Watson, M. D., Cacho, C., Narang, P., Koch, C. T., Ulstrup, S., Ross, F. M., Idrobo, J. 2023; 23 (3): 1068-1076

  Abstract

  The integration of metallic contacts with two-dimensional (2D) semiconductors is routinely required for the fabrication of nanoscale devices. However, nanometer-scale variations in the 2D/metal interface can drastically alter the local optoelectronic properties. Here, we map local excitonic changes of the 2D semiconductor MoS2 in contact with Au. We utilize a suspended and epitaxially grown 2D/metal platform that allows correlated electron energy-loss spectroscopy (EELS) and angle resolved photoelectron spectroscopy (nanoARPES) mapping. Spatial localization of MoS2 excitons uncovers an additional EELS peak related to the MoS2/Au interface. NanoARPES measurements indicate that Au-S hybridization decreases substantially with distance from the 2D/metal interface, suggesting that the observed EELS peak arises due to dielectric screening of the excitonic Coulomb interaction. Our results suggest that increasing the van der Waals distance could optimize excitonic spectra of mixed-dimensional 2D/3D interfaces and highlight opportunities for Coulomb engineering of exciton energies by the local dielectric environment or moiré engineering.

  View details for DOI 10.1021/acs.nanolett.2c04749

  View details for Web of Science ID 000920339100001

  View details for PubMedID 36637381

• Ultrafast X-ray imaging of the light-induced phase transition in VO₂ (Dec, 10.1038/s41567-022-01848-w, 2022) NATURE PHYSICS Johnson, A. S., Perez-Salinas, D., Siddiqui, K. M., Kim, S., Choi, S., Volckaert, K., Majchrzak, P. E., Ulstrup, S., Agarwal, N., Hallman, K., Haglund, R. F., Guenther, C. M., Pfau, B., Eisebitt, S., Backes, D., Maccherozzi, F., Fitzpatrick, A., Dhesi, S. S., Gargiani, P., Valvidares, M., Artrith, N., de Groot, F., Choi, H., Jang, D., Katoch, A., Kwon, S., Park, S., Kim, H., Wall, S. E. 2023; 19 (2): 297

  View details for DOI 10.1038/s41567-023-01949-0

  View details for Web of Science ID 000919544100002

• Van der Waals Engineering of Ultrafast Carrier Dynamics in Magnetic Heterostructures NANO LETTERS Majchrzak, P., Liu, Y., Volckaert, K., Biswas, D., Sahoo, C., Puntel, D., Bronsch, W., Tuniz, M., Cilento, F., Pan, X., Liu, Q., Chen, Y. P., Ulstrup, S. 2023; 23 (2): 414-421

  Abstract

  Heterostructures composed of the intrinsic magnetic topological insulator MnBi2Te4 and its nonmagnetic counterpart Bi2Te3 host distinct surface electronic band structures depending on the stacking order and exposed termination. Here, we probe the ultrafast dynamical response of MnBi2Te4 and MnBi4Te7 following near-infrared optical excitation using time- and angle-resolved photoemission spectroscopy and disentangle surface from bulk dynamics based on density functional theory slab calculations of the surface-projected electronic structure. We gain access to the out-of-equilibrium charge carrier populations of both MnBi2Te4 and Bi2Te3 surface terminations of MnBi4Te7, revealing an instantaneous occupation of states associated with the Bi2Te3 surface layer followed by carrier extraction into the adjacent MnBi2Te4 layers with a laser fluence-tunable delay of up to 350 fs. The ensuing thermal relaxation processes are driven by phonon scattering with significantly slower relaxation times in the magnetic MnBi2Te4 septuple layers. The observed competition between interlayer charge transfer and intralayer phonon scattering demonstrates a method to control ultrafast charge transfer processes in MnBi2Te4-based van der Waals compounds.

  View details for DOI 10.1021/acs.nanolett.2c03075

  View details for Web of Science ID 000912675400001

  View details for PubMedID 36607246

• Ultrafast X-ray imaging of the light-induced phase transition in VO₂ NATURE PHYSICS Johnson, A. S., Perez-Salinas, D., Siddiqui, K. M., Kim, S., Choi, S., Volckaert, K., Majchrzak, P. E., Ulstrup, S., Agarwal, N., Hallman, K., Haglund, R. F., Guenther, C. M., Pfau, B., Eisebitt, S., Backes, D., Maccherozzi, F., Fitzpatrick, A., Dhesi, S. S., Gargiani, P., Valvidares, M., Artrith, N., de Groot, F., Choi, H., Jang, D., Katoch, A., Kwon, S., Park, S., Kim, H., Wall, S. E. 2023; 19 (2): 215-+

  View details for DOI 10.1038/s41567-022-01848-w

  View details for Web of Science ID 000903171600002

• Fermi surface tomography NATURE COMMUNICATIONS Borisenko, S., Fedorov, A., Kuibarov, A., Bianchi, M., Bezguba, V., Majchrzak, P., Hofmann, P., Baumgaertel, P., Voroshnin, V., Kushnirenko, Y., Sanchez-Barriga, J., Varykhalov, A., Ovsyannikov, R., Morozov, I., Aswartham, S., Feia, O., Harnagea, L., Wurmehl, S., Kordyuk, A., Yaresko, A., Berger, H., Buechner, B. 2022; 13 (1): 4132

  Abstract

  Fermi surfaces are essential for predicting, characterizing and controlling the properties of crystalline metals and semiconductors. Angle-resolved photoemission spectroscopy (ARPES) is the only technique directly probing the Fermi surface by measuring the Fermi momenta (kF) from energy- and angular distribution of photoelectrons dislodged by monochromatic light. Existing apparatus is able to determine a number of kF -vectors simultaneously, but direct high-resolution 3D Fermi surface mapping remains problematic. As a result, no such datasets exist, strongly limiting our knowledge about the Fermi surfaces. Here we show that using a simpler instrumentation it is possible to perform 3D-mapping within a very short time interval and with very high resolution. We present the first detailed experimental 3D Fermi surface as well as other experimental results featuring advantages of our technique. In combination with various light sources our methodology and instrumentation offer new opportunities for high-resolution ARPES in the physical and life sciences.

  View details for DOI 10.1038/s41467-022-31841-z

  View details for Web of Science ID 000826101400024

  View details for PubMedID 35840603

  View details for PubMedCentralID PMC9287296

• Spectroscopic view of ultrafast charge carrier dynamics in single- and bilayer transition metal dichalcogenide semiconductors JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA Majchrzak, P., Volckaert, K., Dabo, A., Biswas, D., Bianchi, M., Mahatha, S. K., Dendzik, M., Andreatta, F., Gronborg, S. S., Markovic, I., Riley, J. M., Johannsen, J. C., Lizzit, D., Bignardi, L., Lizzit, S., Cacho, C., Alexander, O., Matselyukh, D., Wyatt, A. S., Chapman, R. T., Springate, E., Lauritsen, J., King, P. D. C., Sanders, C. E., Miwa, J. A., Hofmann, P., Ulstrup, S. 2021; 250

  View details for DOI 10.1016/j.elspec.2021.147093

  View details for Web of Science ID 000670411800009

• Switching of the electron-phonon interaction in 1<i>T</i>-VSe₂ assisted by hot carriers PHYSICAL REVIEW B Majchrzak, P., Pakdel, S., Biswas, D., Jones, A. J. H., Volckaert, K., Markovic, I., Andreatta, F., Sankar, R., Jozwiak, C., Rotenberg, E., Bostwick, A., Sanders, C. E., Zhang, Y., Karras, G., Chapman, R. T., Wyatt, A., Springate, E., Miwa, J. A., Hofmann, P., King, P. D. C., Lanata, N., Chang, Y., Ulstrup, S. 2021; 103 (24)

  View details for DOI 10.1103/PhysRevB.103.L241108

  View details for Web of Science ID 000662305100005

• In Operando Angle-Resolved Photoemission Spectroscopy with Nanoscale Spatial Resolution: Spatial Mapping of the Electronic Structure of Twisted Bilayer Graphene SMALL SCIENCE Majchrzak, P., Muzzio, R., Jones, A. J. H., Curcio, D., Volckaert, K., Biswas, D., Gobbo, J., Singh, S., Robinson, J. T., Watanabe, K., Taniguchi, T., Kim, T. K., Cacho, C., Miwa, J. A., Hofmann, P., Katoch, J., Ulstrup, S. 2021; 1 (6): 2000075

  Abstract

  To pinpoint the electronic and structural mechanisms that affect intrinsic and extrinsic performance limits of 2D material devices, it is of critical importance to resolve the electronic properties on the mesoscopic length scale of such devices under operating conditions. Herein, angle-resolved photoemission spectroscopy with nanoscale spatial resolution (nanoARPES) is used to map the quasiparticle electronic structure of a twisted bilayer graphene device. The dispersion and linewidth of the Dirac cones associated with top and bottom graphene layers are determined as a function of spatial position on the device under both static and operating conditions. The analysis reveals that microscopic rotational domains in the two graphene layers establish a range of twist angles from 9.8° to 12.7°. Application of current and electrostatic gating lead to strong electric fields with peak strengths of 0.75 V/μm at the rotational domain boundaries in the device. These proof-of-principle results demonstrate the potential of nanoARPES to link mesoscale structural variations with electronic states in operating device conditions and to disentangle such extrinsic factors from the intrinsic quasiparticle dispersion.

  View details for DOI 10.1002/smsc.202000075

  View details for Web of Science ID 000914254800002

  View details for PubMedID 40212713

  View details for PubMedCentralID PMC11936027

• Ultrafast Charge Separation in Bilayer WS₂/Graphene Heterostructure Revealed by Time- and Angle-Resolved Photoemission Spectroscopy FRONTIERS IN PHYSICS Krause, R., Chavez-Cervantes, M., Aeschlimann, S., Forti, S., Fabbri, F., Rossi, A., Coletti, C., Cacho, C., Zhang, Y., Majchrzak, P., Chapman, R. T., Springate, E., Gierz, I. 2021; 9

  View details for DOI 10.3389/fphy.2021.668149

  View details for Web of Science ID 000649778400001

• Ultrafast Triggering of Insulator-Metal Transition in Two-Dimensional VSe₂ NANO LETTERS Biswas, D., Jones, A. J. H., Majchrzak, P., Choi, B., Lee, T., Volckaert, K., Feng, J., Markovic, I., Andreatta, F., Kang, C., Kim, H., Lee, I., Jozwiak, C., Rotenberg, E., Bostwick, A., Sanders, C. E., Zhang, Y., Karras, G., Chapman, R. T., Wyatt, A. S., Springate, E., Miwa, J. A., Hofmann, P., King, P. D. C., Chang, Y., Lanata, N., Ulstrup, S. 2021; 21 (5): 1968-1975

  Abstract

  The transition-metal dichalcogenide VSe2 exhibits an increased charge density wave transition temperature and an emerging insulating phase when thinned to a single layer. Here, we investigate the interplay of electronic and lattice degrees of freedom that underpin these phases in single-layer VSe2 using ultrafast pump-probe photoemission spectroscopy. In the insulating state, we observe a light-induced closure of the energy gap, which we disentangle from the ensuing hot carrier dynamics by fitting a model spectral function to the time-dependent photoemission intensity. This procedure leads to an estimated time scale of 480 fs for the closure of the gap, which suggests that the phase transition in single-layer VSe2 is driven by electron-lattice interactions rather than by Mott-like electronic effects. The ultrafast optical switching of these interactions in SL VSe2 demonstrates the potential for controlling phase transitions in 2D materials with light.

  View details for DOI 10.1021/acs.nanolett.0c04409

  View details for Web of Science ID 000629091100010

  View details for PubMedID 33600187

• Observation of Electrically Tunable van Hove Singularities in Twisted Bilayer Graphene from NanoARPES ADVANCED MATERIALS Jones, A. J. H., Muzzio, R., Majchrzak, P., Pakdel, S., Curcio, D., Volckaert, K., Biswas, D., Gobbo, J., Singh, S., Robinson, J. T., Watanabe, K., Taniguchi, T., Kim, T. K., Cacho, C., Lanata, N., Miwa, J. A., Hofmann, P., Katoch, J., Ulstrup, S. 2020; 32 (31): e2001656

  Abstract

  The possibility of triggering correlated phenomena by placing a singularity of the density of states near the Fermi energy remains an intriguing avenue toward engineering the properties of quantum materials. Twisted bilayer graphene is a key material in this regard because the superlattice produced by the rotated graphene layers introduces a van Hove singularity and flat bands near the Fermi energy that cause the emergence of numerous correlated phases, including superconductivity. Direct demonstration of electrostatic control of the superlattice bands over a wide energy range has, so far, been critically missing. This work examines the effect of electrical doping on the electronic band structure of twisted bilayer graphene using a back-gated device architecture for angle-resolved photoemission measurements with a nano-focused light spot. A twist angle of 12.2° is selected such that the superlattice Brillouin zone is sufficiently large to enable identification of van Hove singularities and flat band segments in momentum space. The doping dependence of these features is extracted over an energy range of 0.4 eV, expanding the combinations of twist angle and doping where they can be placed at the Fermi energy and thereby induce new correlated electronic phases in twisted bilayer graphene.

  View details for DOI 10.1002/adma.202001656

  View details for Web of Science ID 000539597000001

  View details for PubMedID 32529706

• Three-dimensional covariance-map imaging of molecular structure and dynamics on the ultrafast timescale COMMUNICATIONS CHEMISTRY Lee, J. W. L., Kockert, H., Heathcote, D., Popat, D., Chapman, R. T., Karras, G., Majchrzak, P., Springate, E., Vallance, C. 2020; 3 (1): 72

  Abstract

  Ultrafast laser pump-probe methods allow chemical reactions to be followed in real time, and have provided unprecedented insight into fundamental aspects of chemical reactivity. While evolution of the electronic structure of the system under study is evident from changes in the observed spectral signatures, information on rearrangement of the nuclear framework is generally obtained indirectly. Disentangling contributions to the signal arising from competing photochemical pathways can also be challenging. Here we introduce the new technique of three-dimensional covariance-map Coulomb explosion imaging, which has the potential to provide complete three-dimensional information on molecular structure and dynamics as they evolve in real time during a gas-phase chemical reaction. We present first proof-of-concept data from recent measurements on CF3I. Our approach allows the contributions from competing fragmentation pathways to be isolated and characterised unambiguously, and is a promising route to enabling the recording of 'molecular movies' for a wide variety of gas-phase chemical processes.

  View details for DOI 10.1038/s42004-020-0320-3

  View details for Web of Science ID 000540432100001

  View details for PubMedID 36703470

  View details for PubMedCentralID PMC9814411

• Momentum-resolved linear dichroism in bilayer MoS₂ PHYSICAL REVIEW B Volckaert, K., Rostami, H., Biswas, D., Markovic, I., Andreatta, F., Sanders, C. E., Majchrzak, P., Cacho, C., Chapman, R. T., Wyatt, A., Springate, E., Lizzit, D., Bignardi, L., Lizzit, S., Mahatha, S. K., Bianchi, M., Lanata, N., King, P. D. C., Miwa, J. A., Balatsky, A., Hofmann, P., Ulstrup, S. 2019; 100 (24)

  View details for DOI 10.1103/PhysRevB.100.241406

  View details for Web of Science ID 000502267000003

• Photodissociation dynamics of CH₃I probed <i>via</i> multiphoton ionisation photoelectron spectroscopy PHYSICAL CHEMISTRY CHEMICAL PHYSICS Warne, E. M., Downes-Ward, B., Woodhouse, J., Parkes, M. A., Bellshaw, D., Springate, E., Majchrzak, P., Zhang, Y., Karras, G., Wyatt, A. S., Chapman, R. T., Kirrander, A., Minns, R. S. 2019; 21 (21): 11142-11149

  Abstract

  The dissociation dynamics of CH3I is investigated on the red (269 nm) and blue (255 nm) side of the absorption maximum of the A-band. Using a multiphoton ionisation probe in a time-resolved photoelectron imaging experiment we observe very different dynamics at the two wavelengths, with significant differences in the measured lifetime and dynamic structure. The differences are explained in terms of changes in excitation cross-sections of the accessible 3Q0 and 1Q1 states and the subsequent dynamics upon each of them. The measurements support the existing literature on the rapid dissociation dynamics on the red side of the absorption maximum at 269 nm which is dominated by the dynamics along the 3Q0 state. At 255 nm we observe similar dynamics along the 3Q0 state but also a significant contribution from the 1Q1 state. The dynamics along the 1Q1 potential show a more complex structure in the photoelectron spectrum and a significantly increased lifetime, indicative of a more complex reaction pathway.

  View details for DOI 10.1039/c9cp01477b

  View details for Web of Science ID 000471025900027

  View details for PubMedID 31094379