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DDC: 530 × Subject: Brillouin zones ×

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Now showing 1 - 4 of 4
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    Visualization of localized perturbations on a (001) surface of the ferromagnetic semimetal EuB6
    (College Park, MD : American Physical Society, 2020) Rößler, S.; Jiao, L.; Seiro, S.; Rosa, P.F.S.; Fisk, Z.; Rößler, U.K.; Wirth, S.
    We performed scanning tunneling microscopy (STM) and spectroscopy on a (001) surface of the ferromagnetic semimetal EuB6. Large-amplitude oscillations emanating from the elastic scattering of electrons by the surface impurities are observed in topography and in differential conductance maps. Fourier transform of the conductance maps embracing these regions indicate a holelike dispersion centered around the Γ point of the two-dimensional Brillouin zone. Using density functional theory slab calculations, we identify a spin-split surface state, which stems from the dangling pz orbitals of the apical boron atom. Hybridization with bulk electronic states leads to a resonance enhancement in certain regions around the Γ point, contributing to the remarkably strong real-space response around static point defects, which are observed in STM measurements.
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    Possible experimental realization of a basic Z 2 topological semimetal in GaGeTe
    (College Park, MD : American Institute of Physics, 2019) Haubold, E.; Fedorov, A.; Pielnhofer, F.; Rusinov, I.P.; Menshchikova, T.V.; Duppel, V.; Friedrich, D.; Weihrich, R.; Pfitzner, A.; Zeugner, A.; Isaeva, A.; Thirupathaiah, S.; Kushnirenko, Y.; Rienks, E.; Kim, T.; Chulkov, E.V.; Büchner, B.; Borisenko, S.
    We report experimental and theoretical evidence that GaGeTe is a basic Z2 topological semimetal with three types of charge carriers: bulk-originated electrons and holes as well as surface state electrons. This electronic situation is qualitatively similar to the classic 3D topological insulator Bi2Se3, but important differences account for an unprecedented transport scenario in GaGeTe. High-resolution angle-resolved photoemission spectroscopy combined with advanced band structure calculations show a small indirect energy gap caused by a peculiar band inversion at the T-point of the Brillouin zone in GaGeTe. An energy overlap of the valence and conduction bands brings both electron and holelike carriers to the Fermi level, while the momentum gap between the corresponding dispersions remains finite. We argue that peculiarities of the electronic spectrum of GaGeTe have a fundamental importance for the physics of topological matter and may boost the material's application potential.
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    Formation of heavy d-electron quasiparticles in Sr3Ru2O7
    (Milton Park : Taylor & Francis, 2013) Allan, M.P.; Tamai, A.; Rozbicki, E.; Fischer, M.H.; Voss, J.; King, P.D.C.; Meevasana, W.; Thirupathaiah, S.; Rienks, E.; Fink, J.; Tennant, D.A .; Perry, R.S.; Mercure, J.F.; Wang, M.A.; Lee, Jinho; Fennie, C.J.; Kim, E.A.; Lawler, M.J.; Shen, K.M.; Mackenzie, A.P.; Shen, Z.X.; Baumberger, F.
    The phase diagram of Sr3Ru2O7 shows hallmarks of strong electron correlations despite the modest Coulomb interaction in the Ru 4d shell. We use angle-resolved photoelectron spectroscopy measurements to provide microscopic insight into the formation of the strongly renormalized heavy d-electron liquid that controls the physics of Sr3Ru2O7. Our data reveal itinerant Ru 4d-states confined over large parts of the Brillouin zone to an energy range of <6 meV, nearly three orders of magnitude lower than the bare band width. We show that this energy scale agrees quantitatively with a characteristic thermodynamic energy scale associated with quantum criticality and illustrate how it arises from a combination of back-folding due to a structural distortion and the hybridization of light and strongly renormalized, heavy quasiparticle bands. The resulting heavy Fermi liquid has a marked k-dependence of the renormalization which we relate to orbital mixing along individual Fermi surface sheets.
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    Sub-cycle valleytronics: control of valley polarization using few-cycle linearly polarized pulses
    (Washington, DC : OSA, 2021) Jiménez-Galán, Álvaro; Silva, Rui E. F.; Smirnova, Olga; Ivanov, Misha
    So far, it has been assumed that selective excitation of a desired valley in the Brillouin zone of a hexagonal two-dimensional material has to rely on using circularly polarized fields. We theoretically demonstrate a way to control the valley excitation in hexagonal 2D materials on a few-femtosecond timescale using a few-cycle, linearly polarized pulse with controlled carrier–envelope phase. The valley polarization is mapped onto the strength of the perpendicular harmonic signal of a weak, linearly polarized pulse, which allows to read this information all-optically without destroying the valley state and without relying on the Berry curvature, making our approach potentially applicable to inversion-symmetric materials. We show applicability of this method to hexagonal boron nitride and MoS2.