Dr. François C. Bocquet (Posseik) » People

@article{Stettner2026,

title = {Tracing the film structure of an organic semiconductor with photoemission orbital tomography},

author = {M. Stettner and S. Kaidisch and Andrey V. Matetskiy and E. Fackelman and S. Soubatch and C. Kumpf and F. C. Bocquet and M. G. Ramsey and P. Puschnig and F. S. Tautz},

url = {https://arxiv.org/abs/2603.06204},

doi = {10.48550/arXiv.2603.06204},

year  = {2026},

date = {2026-03-06},

journal = {arXiv:2603.06204 [cond-mat.mtrl-sci]},

keywords = {},

pubstate = {forthcoming},

tppubtype = {article}

}

@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{Haags2026,

title = {Multi-Orbital Charge Transfer into Nonplanar Cycloarenes Revealed with CO-Functionalized STM Tips},

author = {A. Haags and A. Reichmann and Z. Ruan and Q. Fan and L. Egger and H. Kirschner and T. Naumann and S. Werner and O. Kleykamp and J. Martinez Castro and F. Lüpke and F. C. Bocquet and C. Kumpf and S. Soubatch and A. Gottwald and G. Koller and M. G. Ramsey and M. Richter and J. Sundermeyer and P. Puschnig and J. M. Gottfried and F. S. Tautz and S. Wenzel},

url = {https://pubs.acs.org/doi/10.1021/acs.jpclett.5c03268},

doi = {10.1021/acs.jpclett.5c03268},

year  = {2026},

date = {2026-01-21},

journal = {The Journal of Physical Chemistry Letters},

volume = {17},

issue = {5},

pages = {1296–1304},

abstract = {On-surface synthesis enables the tunable preparation of diverse molecular systems with tailored properties. Recently, the highly selective synthesis of kekulene (>99%) on Cu(111) and isokekulene (92%) on Cu(110) from the same molecular precursor was demonstrated. Scanning tunneling microscopy (STM) with CO-functionalized tips can identify individual molecules based on their geometric structure at low coverage on Cu(110) but also reveals complex features arising from electronic contributions near the Fermi energy. Here, we investigate the origin of these features by simulating STM images based on a weighted sum of multiple molecular orbitals, for which we employ weights based on the calculated molecular-orbital projected density of states. This analysis provides direct experimental evidence for charge transfer from the surface into multiple formerly unoccupied molecular orbitals for single molecules of kekulene as well as isokekulene in its two nonplanar adsorption configurations. In comparison, the area-integrating photoemission orbital tomography technique confirms the charge transfer as well as the high selectivity for the formation of a full monolayer of predominantly isokekulene on Cu(110). Our STM-based approach is applicable to a wide range of adsorbed molecular systems and specifically also suited for strongly interacting surfaces, nonplanar molecules, and compounds accessible only in extremely low yields.},

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{Haags2025b,

title = {Tomographic identification of all molecular orbitals in a wide binding-energy range},

author = {A. Haags and D. Brandstetter and X. Yang and L. Egger and H. Kirschner and A. Gottwald and M. Richter and G. Koller and F. C. Bocquet and C. Wagner and M. G. Ramsey and S. Soubatch and P. Puschnig and F. S. Tautz},

doi = {10.1103/physrevb.111.165402},

issn = {2469-9969},

year  = {2025},

date = {2025-04-00},

urldate = {2025-04-00},

journal = {Phys. Rev. B},

volume = {111},

number = {16},

publisher = {American Physical Society (APS)},

abstract = {<jats:p>In the past decade, photoemission orbital tomography (POT) has evolved into a powerful tool to investigate the electronic structure of organic molecules adsorbed on surfaces. Here we show that POT allows for the comprehensive experimental identification of all molecular orbitals in a substantial binding energy range of more than 10 eV. Making use of the angular distribution of photoelectrons as a function of binding-energy, we exemplify this by extracting an orbital-resolved projected density of states for 15 <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mi>π</a:mi></a:math> and 23 <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mi>σ</b:mi></b:math> orbitals from the experimental data of the prototypical organic molecule bisanthene (<c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:msub><c:mi mathvariant="normal">C</c:mi><c:mn>28</c:mn></c:msub><c:msub><c:mi mathvariant="normal">H</c:mi><c:mn>14</c:mn></c:msub></c:mrow></c:math>) on a Cu(110) surface. These experimental results for an essentially complete set of orbitals within the given binding-energy range serve as stringent benchmarks for electronic structure methods, which we illustrate by performing density functional calculations employing four frequently used exchange-correlation functionals. By computing the respective molecular-orbital-projected densities of states, a one-to-one comparison with experimental data for an unprecedented number of 38 orbital energies became possible. The quantitative analysis of our data reveals that the range-separated hybrid functional HSE performs best for the investigated organic/metal interface. At a more fundamental level, the remarkable agreement between the experimental and the Kohn-Sham orbital energies over a binding-energy range larger than 10 eV suggests that—perhaps unexpectedly—Kohn-Sham orbitals approximate Dyson orbitals, which would rigorously account for the electron extraction process in photoemission spectroscopy but are notoriously difficult to compute, in a much better way than previously thought.</jats:p>

          <jats:sec>

            <jats:title/>

            <jats:supplementary-material>

              <jats:permissions>

                <jats:copyright-statement>Published by the American Physical Society</jats:copyright-statement>

                <jats:copyright-year>2025</jats:copyright-year>

              </jats:permissions>

            </jats:supplementary-material>

          </jats:sec>},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nakayama2025b,

title = {Anisotropic dispersion of excitonic bands of the single-crystal pentacene (001) surface as measured by low-energy angle-resolved high-resolution electron energy-loss spectroscopy},

author = {Y. Nakayama and F. C. Bocquet and R. Tsuruta and S. Soubatch and F. S. Tautz},

url = {https://www.sciencedirect.com/science/article/pii/S0368204825000015},

doi = {10.1016/j.elspec.2025.147514},

year  = {2025},

date = {2025-01-31},

journal = {Journal of Electron Spectroscopy and Related Phenomena},

volume = {279},

issue = {147514},

abstract = {Low-energy high-resolution electron energy-loss spectroscopy (HREELS) is a useful technique for the charac-

terization of various excitation processes at solid surfaces. However, no successful work has been reported on

molecular single-crystal samples yet. In the present study, low-energy angle-resolved HREELS measurements

were conducted on single-crystal pentacene, an organic semiconductor. The results confirmed the excitonic

bands exhibiting energy–momentum dispersion and anisotropy of these depending on the surface crystallo-

graphic directions, corroborating the occurrence of exciton delocalization, contrary to the ordinary notion of the

Frenkel exciton for weakly interacting van der Waals molecular solids. The present results demonstrate that low-

energy angle-resolved HREELS is applicable to the precise examination of the excitonic characteristics of solid-

state surfaces, even for molecular semiconductor single crystals.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Haags2025,

title = {Tomographic identification of all molecular orbitals in a wide binding energy range},

author = {A. Haags and D. Brandstetter and X. Yang and L. Egger and H. Kirschner and A. Gottwald and M. Richter and G. Koller and F. C. Bocquet and C. Wagner and M. G. Ramsey and S. Soubatch and P. Puschnig and F. S. Tautz},

url = {https://arxiv.org/abs/2501.05287},

year  = {2025},

date = {2025-01-09},

urldate = {2025-01-09},

journal = {ArXiv},

abstract = {In the past decade, photoemission orbital tomography (POT) has evolved into a powerful tool to investigate the electronic structure of organic molecules adsorbed on surfaces. Here we show that POT allows for the comprehensive experimental identification of all molecular orbitals in a substantial binding energy range, in the present case more than 10 eV. Making use of the angular distribution of photoelectrons as a function of binding energy, we exemplify this by extracting orbital-resolved partial densities of states (pDOS) for 15 π and 23 σ orbitals from the experimental photoemission intensities of the prototypical organic molecule bisanthene (C28H14) on a Cu(110) surface. In their entirety, these experimentally measured orbital-resolved pDOS for an essentially complete set of orbitals serve as a stringent benchmark for electronic structure methods, which we illustrate by performing density functional theory (DFT) calculations employing four frequently-used exchange-correlation functionals. By computing the respective molecular-orbital-projected densities of states of the bisanthene/Cu(110) interface, a one-to-one comparison with experimental data for an unprecedented number of 38 orbital energies becomes possible. The quantitative analysis of our data reveals that the range-separated hybrid functional HSE performs best for the investigated organic/metal interface. At a more fundamental level, the remarkable agreement between the experimental and the Kohn-Sham orbital energies over a binding energy range larger than 10,eV suggests that -- perhaps unexpectedly -- Kohn-Sham orbitals approximate Dyson orbitals, which would rigorously account for the electron extraction process in photoemission spectroscopy but are notoriously difficult to compute, in a much better way than previously thought. },

keywords = {},

pubstate = {forthcoming},

tppubtype = {article}

}

@article{Adamkiewicz2023,

title = {Coherent and Incoherent Excitation Pathways in Time-Resolved Photoemission Orbital Tomography of CuPc/Cu(001)-2O},

author = {A. Adamkiewicz and M. Raths and M. Stettner and M. Theilen and L. Münster and S. Wenzel and M. Hutter and S. Soubatch and C. Kumpf and F. C. Bocquet and R. Wallauer and F. S. Tautz and U. Höfer},

doi = {10.1021/acs.jpcc.3c04859},

year  = {2023},

date = {2023-10-09},

urldate = {2023-10-09},

journal = {J.Phys. Chem. C},

volume = {127},

pages = {20411},

abstract = {Time-resolved photoemission orbital tomography (tr-POT) offers unique possibilities for tracing molecular electron dynamics. The recorded pump-induced changes of the angle-resolved photoemission intensities allow one to characterize unoccupied molecular states in momentum space and to deduce the incoherent temporal evolution of their population. Here, we show for the example of CuPc/Cu(001)-2O that the method also gives access to the coherent regime and that different excitation pathways can be disentangled by a careful analysis of the time-dependent change of the photoemission momentum pattern. In particular, we demonstrate by varying photon energy and polarization of the pump light how the incoherent temporal evolution of the LUMO distribution can be distinguished from coherent contributions of the projected HOMO. Moreover, we report the selective excitation of molecules with a specific orientation at normal incidence by aligning the electric field of the pump light along the molecular axis.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kern2023b,

title = {Simple extension of the plane-wave final state in photoemission: Bringing understanding to the photon-energy dependence of two-dimensional materials},

author = {C. S. Kern and A. Haags and L.Egger and X. Yang and H. Kirschner and S. Wolff and T. Seyller and A. Gottwald and M. Richter and U. De Giovannini and A. Rubio and M. G. Ramsey and F. C. Bocquet and Soubatch and F. S. Tautz and P. Puschnig and S. Moser},

url = {https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.5.033075},

doi = {10.1103/PhysRevResearch.5.033075},

year  = {2023},

date = {2023-08-03},

journal = {Phys. Rev. Research},

volume = {5},

issue = {033075},

abstract = {Angle-resolved photoemission spectroscopy (ARPES) is a method that measures orbital and band structure contrast through the momentum distribution of photoelectrons. Its simplest interpretation is obtained in the plane-wave approximation, according to which photoelectrons propagate freely to the detector. The photoelectron momentum distribution is then essentially given by the Fourier transform of the real-space orbital. While the plane-wave approximation is remarkably successful in describing the momentum distributions of aromatic compounds, it generally fails to capture kinetic-energy-dependent final-state interference and dichroism effects. Focusing our present study on quasi-freestanding monolayer graphene as the archetypical two-dimensional (2D) material, we observe an exemplary 𝐸kin

-dependent modulation of, and a redistribution of spectral weight within, its characteristic horseshoe signature around the

‾‾‾

K

and

‾‾‾

K

′

points: both effects indeed cannot be rationalized by the plane-wave final state. Our data are, however, in remarkable agreement with ab initio time-dependent density functional simulations of a freestanding graphene layer and can be explained by a simple extension of the plane-wave final state, permitting the two dipole-allowed partial waves emitted from the C 2⁢𝑝𝑧

orbitals to scatter in the potential of their immediate surroundings. Exploiting the absolute photon flux calibration of the Metrology Light Source, this scattered-wave approximation allows us to extract 𝐸kin

-dependent amplitudes and phases of both partial waves directly from photoemission data. The scattered-wave approximation thus represents a powerful yet intuitive refinement of the plane-wave final state in photoemission of 2D materials and beyond.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Haags2021,

title = {Momentum-space imaging of σ-orbitals for chemical analysis},

author = {A. Haags and X. Yang and L. Egger and D. Brandstetter and H. Kirschner and F. C. Bocquet and G. Koller and A. Gottwald and M. Richter and J. M. Gottfried and M. G. Ramsey and P. Puschnig and S. Soubatch and F. S. Tautz},

doi = {10.1126/sciadv.abn0819},

year  = {2022},

date = {2022-01-01},

urldate = {2022-01-01},

journal = {Sci. Adv.},

volume = {8},

pages = {eabn0819},

abstract = {Tracing the modifications of molecules in surface chemical reactions benefits from the possibility to image their orbitals. While delocalized frontier orbitals with π character are imaged routinely with photoemission orbital tomography, they are not always sensitive to local chemical modifications, particularly the making and breaking of bonds at the molecular periphery. For such bonds, σ orbitals would be far more revealing. Here, we show that these orbitals can indeed be imaged in a remarkably broad energy range and that the plane wave approximation, an important ingredient of photoemission orbital tomography, is also well fulfilled for these orbitals. This makes photoemission orbital tomography a unique tool for the detailed analysis of surface chemical reactions. We demonstrate this by identifying the reaction product of a dehalogenation and cyclodehydrogenation reaction.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hurdax2022,

title = {Large Distortion of Fused Aromatics on Dielectric Interlayers Quantified by Photoemission Orbital Tomography},

author = {P. Hurdax and C. S. Kern and T. G. Boné and A. Haags and M. Hollerer and L. Egger and X. Yang and H. Kirschner and A. Gottwald and M. Richter and F. C. Bocquet and S. Soubatch and G. Koller and F. S. Tautz and M. Sterrer and P. Puschnig and M. G. Ramsey},

doi = {10.1021/acsnano.2c08631},

year  = {2022},

date = {2022-01-01},

journal = {ACS Nano},

volume = {16},

pages = {17435-17443},

abstract = {Polycyclic aromatic compounds with fused benzene rings offer an extraordinary versatility as next-generation organic semiconducting materials for nanoelectronics and optoelectronics due to their tunable characteristics, including charge-carrier mobility and optical absorption. Nonplanarity can be an additional parameter to customize their electronic and optical properties without changing the aromatic core. In this work, we report a combined experimental and theoretical study in which we directly observe large, geometry-induced modifications in the frontier orbitals of a prototypical dye molecule when adsorbed on an atomically thin dielectric interlayer on a metallic substrate. Experimentally, we employ angle-resolved photoemission experiments, interpreted in the framework of the photoemission orbital tomography technique. We demonstrate its sensitivity to detect geometrical bends in adsorbed molecules and highlight the role of the photon energy used in experiment for detecting such geometrical distortions. Theoretically, we conduct density functional calculations to determine the geometric and electronic structure of the adsorbed molecule and simulate the photoemission angular distribution patterns. While we found an overall good agreement between experimental and theoretical data, our results also unveil limitations in current van der Waals corrected density functional approaches for such organic/dielectric interfaces. Hence, photoemission orbital tomography provides a vital experimental benchmark for such systems. By comparison with the state of the same molecule on a metallic substrate, we also offer an explanation why the adsorption on the dielectric induces such large bends in the molecule.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Wallauer2020,

title = {Tracing orbital images on ultrafast time scales},

author = {R. Wallauer and M. Raths and K. Stallberg and L. Münster and D. Brandstetter and X. Yang and J. Güdde and P. Puschnig and S. Soubatch and C. Kumpf and F. C. Bocquet and F. S. Tautz and U. Höfer},

doi = {10.1126/science.abf3286},

year  = {2021},

date = {2021-01-01},

urldate = {2021-01-01},

journal = {Science},

volume = {371},

pages = {1056-1059},

abstract = {Frontier orbitals determine fundamental molecular properties such as chemical reactivities. Although electron distributions of occupied orbitals can be imaged in momentum space by photoemission tomography, it has so far been impossible to follow the momentum-space dynamics of a molecular orbital in time, for example, through an excitation or a chemical reaction. Here, we combined time-resolved photoemission using high laser harmonics and a momentum microscope to establish a tomographic, femtosecond pump-probe experiment of unoccupied molecular orbitals. We measured the full momentum-space distribution of transiently excited electrons, connecting their excited-state dynamics to real-space excitation pathways. Because in molecules this distribution is closely linked to orbital shapes, our experiment may, in the future, offer the possibility of observing ultrafast electron motion in time and space.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}