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DDC: 540 × Subject: photoemission ×

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    Multidimensional high harmonic spectroscopy of polyatomic molecules: detecting sub-cycle laser-driven hole dynamics upon ionization in strong mid-IR laser fields
    (Cambridge [u.a.] : Soc., 2016) Bruner, Barry D.; Mašín, Zdeněk; Negro, Matteo; Morales, Felipe; Brambila, Danilo; Devetta, Michele; Faccialà, Davide; Harvey, Alex G.; Ivanov, Misha; Mairesse, Yann; Patchkovskii, Serguei; Serbinenko, Valeria; Soifer, Hadas; Stagira, Salvatore; Vozzi, Caterina; Dudovich, Nirit; Smirnova, Olga
    High harmonic generation (HHG) spectroscopy has opened up a new frontier in ultrafast science, where electronic dynamics can be measured on an attosecond time scale. The strong laser field that triggers the high harmonic response also opens multiple quantum pathways for multielectron dynamics in molecules, resulting in a complex process of multielectron rearrangement during ionization. Using combined experimental and theoretical approaches, we show how multi-dimensional HHG spectroscopy can be used to detect and follow electronic dynamics of core rearrangement on sub-laser cycle time scales. We detect the signatures of laser-driven hole dynamics upon ionization and reconstruct the relative phases and amplitudes for relevant ionization channels in a CO2 molecule on a sub-cycle time scale. Reconstruction of channel-resolved complex ionization amplitudes on attosecond time scales has been a long-standing goal of high harmonic spectroscopy. Our study brings us one step closer to fulfilling this initial promise and developing robust schemes for sub-femtosecond imaging of multielectron rearrangement in complex molecular systems.
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    Contrast Reversal in Scanning Tunneling Microscopy and Its Implications for the Topological Classification of SmB6
    (Weinheim : Wiley-VCH, 2020) Herrmann, Hannes; Hlawenka, Peter; Siemensmeyer, Konrad; Weschke, Eugen; Sánchez-Barriga, Jaime; Varykhalov, Andrei; Shitsevalova, Natalya Y.; Dukhnenko, Anatoliy V.; Filipov, Volodymyr B.; Gabáni, Slavomir; Flachbart, Karol; Rader, Oliver; Sterrer, Martin; Rienks, Emile D.L.
    SmB6 has recently attracted considerable interest as a candidate for the first strongly correlated topological insulator. Such materials promise entirely new properties such as correlation-enhanced bulk bandgaps or a Fermi surface from spin excitations. Whether SmB6 and its surface states are topological or trivial is still heavily disputed however, and a solution is hindered by major disagreement between angle-resolved photoemission (ARPES) and scanning tunneling microscopy (STM) results. Here, a combined ARPES and STM experiment is conducted. It is discovered that the STM contrast strongly depends on the bias voltage and reverses its sign beyond 1 V. It is shown that the understanding of this contrast reversal is the clue to resolving the discrepancy between ARPES and STM results. In particular, the scanning tunneling spectra reflect a low-energy electronic structure at the surface, which supports a trivial origin of the surface states and the surface metallicity of SmB6. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim