Prof. Dr. Rupert Huber » 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{Ito2023,

title = {Build-up and dephasing of Floquet-Bloch bands on subcycle timescales},

author = {S. Ito and M. Schüler and M. Meierhofer and S. Schlauderer and J. Freudenstein and R. Reimann and D. Afanasiev and K. A. Kokh and O. E. Tereshchenko and J. Güdde and M. A. Sentef and U. Höfer and R. Huber

},

doi = {10.1038/s41586-023-05850-x},

year  = {2023},

date = {2023-04-12},

urldate = {2023-04-12},

journal = {Nature},

volume = {616},

pages = {pages 696–701},

abstract = {Strong light fields have created opportunities to tailor novel functionalities of solids. Floquet–Bloch states can form under periodic driving of electrons and enable exotic quantum phases. On subcycle timescales, lightwaves can simultaneously drive intraband currents and interband transition, which enable high-harmonic generation and pave the way towards ultrafast electronics. Yet, the interplay of intraband and interband excitations and their relation to Floquet physics have been key open questions as dynamical aspects of Floquet states have remained elusive. Here we provide this link by visualizing the ultrafast build-up of Floquet–Bloch bands with time-resolved and angle-resolved photoemission spectroscopy. We drive surface states on a topological insulator with mid-infrared fields—strong enough for high-harmonic generation—and directly monitor the transient band structure with subcycle time resolution. Starting with strong intraband currents, we observe how Floquet sidebands emerge within a single optical cycle; intraband acceleration simultaneously proceeds in multiple sidebands until high-energy electrons scatter into bulk states and dissipation destroys the Floquet bands. Quantum non-equilibrium calculations explain the simultaneous occurrence of Floquet states with intraband and interband dynamics. Our joint experiment and theory study provides a direct time-domain view of Floquet physics and explores the fundamental frontiers of ultrafast band-structure engineering.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Freudenstein2022,

title = {Attosecond clocking of correlations between Bloch electrons},

author = {J. Freudenstein and M. Borsch and M. Meierhofer and D. Afanasiev and C. P. Schmid and F. Sandner and M. Liebich and A. Girnghuber and M. Knorr and M. Kira and R. Huber},

doi = {10.1038/s41586-022-05190-2},

year  = {2022},

date = {2022-10-12},

urldate = {2022-10-12},

journal = {Nature},

volume = {610},

pages = {290--295},

abstract = {Delocalized Bloch electrons and the low-energy correlations between them determine key optical, electronic and entanglement functionalities of solids, all the way through to phase transitions. To directly capture how many-body correlations affect the actual motion of Bloch electrons, subfemtosecond (1 fs = 10−15 s) temporal precision is desirable. Yet, probing with attosecond (1 as = 10−18 s) high-energy photons has not been energy-selective enough to resolve the relevant millielectronvolt-scale interactions of electrons near the Fermi energy. Here, we use multi-terahertz light fields to force electron–hole pairs in crystalline semiconductors onto closed trajectories, and clock the delay between separation and recollision with 300 as precision, corresponding to 0.7% of the driving field’s oscillation period. We detect that strong Coulomb correlations emergent in atomically thin WSe2 shift the optimal timing of recollisions by up to 1.2 ± 0.3 fs compared to the bulk material. A quantitative analysis with quantum-dynamic many-body computations in a Wigner-function representation yields a direct and intuitive view on how the Coulomb interaction, non-classical aspects, the strength of the driving field and the valley polarization influence the dynamics. The resulting attosecond chronoscopy of delocalized electrons could revolutionize the understanding of unexpected phase transitions and emergent quantum-dynamic phenomena for future electronic, optoelectronic and quantum-information technologies.},

keywords = {},

pubstate = {published},

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}

}

@article{Reimann2018,

title = {Subcycle observation of lightwave-driven Dirac currents in a topological surface band},

author = {J. Reimann and S. Schlauderer and C. P. Schmid and F. Langer and S. Baierl and K. A. Kokh and O. E. Tereshchenko and A. Kimura and C. Lange and J. Güdde and U. Höfer and R. Huber},

doi = {10.1038/s41586-018-0544-x},

year  = {2018},

date = {2018-01-01},

journal = {Nature},

volume = {562},

pages = {396--400},

abstract = {Harnessing the carrier wave of light as an alternating-current bias may enable electronics at optical clock rates1. Lightwave-driven currents have been assumed to be essential for high-harmonic generation in solids2–6, charge transport in nanostructures7,8, attosecond-streaking experiments9–16 and atomic-resolution ultrafast microscopy17,18. However, in conventional semiconductors and dielectrics, the finite effective mass and ultrafast scattering of electrons limit their ballistic excursion and velocity. The Dirac-like, quasi-relativistic band structure of topological insulators19–29 may allow these constraints to be lifted and may thus open a new era of lightwave electronics. To understand the associated, complex motion of electrons, comprehensive experimental access to carrier-wave-driven currents is crucial. Here we report angle-resolved photoemission spectroscopy with subcycle time resolution that enables us to observe directly how the carrier wave of a terahertz light pulse accelerates Dirac fermions in the band structure of the topological surface state of Bi2Te3. While terahertz streaking of photoemitted electrons traces the electromagnetic field at the surface, the acceleration of Dirac states leads to a strong redistribution of electrons in momentum space. The inertia-free surface currents are protected by spin–momentum locking and reach peak densities as large as two amps per centimetre, with ballistic mean free paths of several hundreds of nanometres, opening up a realistic parameter space for all-coherent lightwave-driven electronic devices. Furthermore, our subcycle-resolution analysis of the band structure may greatly improve our understanding of electron dynamics and strong-field interaction in solids.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Cocker2016,

title = {Tracking the ultrafast motion of a single molecule by femtosecond orbital imaging},

author = {T. L. Cocker and D. Peller and P. Yu and J. Repp and R. Huber},

doi = {10.1038/nature19816},

year  = {2016},

date = {2016-01-01},

urldate = {2020-06-09},

journal = {Nature},

volume = {539},

pages = {263--267},

abstract = {Watching a single molecule move calls for measurements that combine ultrafast temporal resolution with atomic spatial resolution; this is now shown to be possible by combining scanning tunnelling microscopy with lightwave electronics, through a technique that involves removing a single electron from the highest occupied orbital of a single pentacene molecule in a time window shorter than an oscillation cycle of light.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}