Sarah Zajusch » People

@article{Eggers2026,

title = {Subcycle videography of lightwave-driven Landau-Zener-Majorana transitions in graphene},

author = {V. Eggers and G. Inzani and M. Meierhofer and L. Münster and J. Helml and R. Wallauer and S. Zajusch and S. Ito and L. Machtl and H. Yin and C. Kumpf and F. C. Bocquet and C. Bao and J. Güdde and F. S. Tautz and R. Huber and U. Höfer},

url = {https://arxiv.org/abs/2602.12844},

doi = {10.48550/arXiv.2602.12844},

year  = {2026},

date = {2026-02-13},

journal = {arXiv:2602.12844 [cond-mat.mes-hall]},

abstract = {Strong light fields have unlocked previously unthinkable possibilities to tailor coherent electron trajectories, engineer band structures and shape emergent phases of matter all-optically. Unravelling the underlying quantum mechanisms requires a visualisation of the lightwave-driven electron motion directly in the band structure. While photoelectron momentum microscopy has imaged optically excited electrons averaged over many cycles of light, actual subcycle band-structure videography has been limited to small electron momenta. Yet lightwave-driven elementary processes in quantum materials often occur throughout momentum space. Here, we introduce attosecond-precision, subcycle band-structure videography covering the entire first Brillouin zone (BZ) and visualize one of the most fundamental but notoriously elusive strong-field processes: non-adiabatic Landau-Zener-Majorana (LZM) tunnelling. The interplay of field-driven acceleration within the Dirac-like band structure of graphene and periodic LZM interband tunnelling manifest in a coherent displacement and distortion of the momentum distribution at the BZ edge. The extremely non-thermal electron distributions also allow us to disentangle competing scattering processes and assess their impact on coherent electronic control through electron redistribution and thermalization. Our panoramic view of strong-field-driven electron motion in quantum materials lays the foundation for a microscopic understanding of some of the most discussed light-driven phenomena in condensed matter physics. },

keywords = {},

pubstate = {forthcoming},

tppubtype = {article}

}

@article{Bao2026,

title = {Observation of an isolated flat band in the van der Waals crystal NbOCl2},

author = {C. Bao and V. Eggers and M. Meierhofer and J. Helml and L. Münster and S. Ito and L. Machtl and S. Zajusch and G. Inzani and L. Wittmann and M. Liebich and R. Wallauer and U. Höfer and R. Huber},

url = {https://www.nature.com/articles/s43246-025-01070-0},

doi = {10.1038/s43246-025-01070-0},

year  = {2026},

date = {2026-01-10},

journal = {Communications Materials},

volume = {7},

number = {60},

abstract = {Dispersionless electronic bands lead to an extremely high density of states and suppressed kinetic energy, thereby increasing electronic correlations and instabilities that can shape emergent ordered states, such as excitonic, ferromagnetic, and superconducting phases. A flat band that extends over the entire momentum space and is well isolated from other dispersive bands is, therefore, particularly interesting. Here, the band structure of the van der Waals crystal NbOCl2 is revealed by utilizing photoelectron momentum microscopy. We directly map out an electronic band that is flat throughout the entire Brillouin zone and features a width of only  ~ 100 meV. This band is well isolated from both the conduction and remote valence bands. Moreover, the quasiparticle band gap shows a high tunability upon the deposition of cesium atoms on the surface. By combining the single-particle band structure with the optical transmission spectrum, the optical gap is identified. The fully isolated flat band in a van der Waals crystal provides a qualitatively new testbed for exploring flat-band physics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Theilen2025,

title = {Observing the spatial and temporal evolution of exciton wave functions},

author = {M. Theilen and S. Kaidisch and M. Stettner and S. Zajusch and E. Fackelman and A. Adamkiewicz and R. Wallauer and A. Windischbacher and C. S. Kern and M. G. Ramsey and F. C. Bocquet and S. Soubatch and F. S. Tautz and U. Höfer and P. Puschnig},

url = {https://arxiv.org/abs/2511.23001},

doi = {10.48550/arXiv.2511.23001},

year  = {2025},

date = {2025-11-28},

urldate = {2025-11-28},

journal = { arXiv:2511.23001  [cond-mat.mtrl-sci]},

abstract = {Excitons, the correlated electron-hole pairs governing optical and transport properties in organic semiconductors, have long resisted direct experimental access to their full quantum-mechanical wave functions. Here, we use femtosecond time-resolved photoemission orbital tomography (trPOT), combining high-harmonic probe pulses with time- and momentum-resolved photoelectron spectroscopy, to directly image the momentum-space distribution and ultrafast dynamics of excitons in  -sexithiophene thin films. We introduce a quantitative model that enables reconstruction of the exciton wave function in real space, including both its spatial extent and its internal phase structure. The reconstructed wave function reveals coherent delocalization across approximately three molecular units and exhibits a characteristic phase modulation, consistent with ab initio calculations within the framework of many-body perturbation theory. Time-resolved measurements further show a  % contraction of the exciton radius within 400 fs, providing direct evidence of self-trapping driven by exciton-phonon coupling. These results establish trPOT as a general and experimentally accessible approach for resolving exciton wave functions -- with spatial, phase, and temporal sensitivity -- in a broad class of molecular and low-dimensional materials. },

keywords = {},

pubstate = {forthcoming},

tppubtype = {article}

}

@article{Wallauer2021,

title = {Momentum-Resolved Observation of Exciton Formation Dynamics in Monolayer WS2},

author = {R. Wallauer and R. Perea-Causin and L. Münster and S. Zajusch and S. Brem and J. Güdde and K. Tanimura and K. -Q. Lin and R. Huber and E. Malic and U. Höfer},

doi = {10.1021/acs.nanolett.1c01839},

year  = {2021},

date = {2021-01-01},

journal = {Nano Lett.},

volume = {21},

pages = {5867--5873},

abstract = {The dynamics of momentum-dark exciton formation in transition metal dichalcogenides is difficult to measure experimentally, as many momentum-indirect exciton states are not accessible to optical interband spectroscopy. Here, we combine a tunable pump, high-harmonic probe laser source with a 3D momentum imaging technique to map photoemitted electrons from monolayer WS2. This provides momentum-, energy- and time-resolved access to excited states on an ultrafast time scale. The high temporal resolution of the setup allows us to trace the early-stage exciton dynamics on its intrinsic time scale and observe the formation of a momentum-forbidden dark KΣ exciton a few tens of femtoseconds after optical excitation. By tuning the excitation energy, we manipulate the temporal evolution of the coherent excitonic polarization and observe its influence on the dark exciton formation. The experimental results are in excellent agreement with a fully microscopic theory, resolving the temporal and spectral dynamics of bright and dark excitons in WS2.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}