1. Germanium Monosulfide as a Natural Platform for Highly Anisotropic THz Polaritons
- Author
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Tobias Nörenberg, Gonzalo Álvarez-Pérez, Maximilian Obst, Lukas Wehmeier, Franz Hempel, J. Michael Klopf, Alexey Y. Nikitin, Susanne C. Kehr, Lukas M. Eng, Pablo Alonso-González, Thales V. A. G. de Oliveira, Helmholtz-Zentrum Dresden-Rossendorf, Helmholtz Association, Federal Ministry of Education and Research (Germany), German Research Foundation, Agencia Estatal de Investigación (España), Ministerio de Ciencia, Innovación y Universidades (España), Eusko Jaurlaritza, Principado de Asturias, and European Research Council
- Subjects
Condensed Matter - Materials Science ,van der Waals materials ,Condensed Matter - Mesoscale and Nanoscale Physics ,General Engineering ,Physics::Optics ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,General Physics and Astronomy ,optical anisotropy ,terahertz ,phonon polaritons ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,General Materials Science ,polariton interferometry ,Physics - Optics ,Optics (physics.optics) - Abstract
Terahertz (THz) electromagnetic radiation is key to access collective excitations such as magnons (spins), plasmons (electrons), or phonons (atomic vibrations), thus bridging topics between optics and solid-state physics. Confinement of THz light to the nanometer length scale is desirable for local probing of such excitations in low-dimensional systems, thereby circumventing the large footprint and inherently low spectral power density of far-field THz radiation. For that purpose, phonon polaritons (PhPs) in anisotropic van der Waals (vdW) materials have recently emerged as a promising platform for THz nanooptics. Hence, there is a demand for the exploration of materials that feature not only THz PhPs at different spectral regimes but also host anisotropic (directional) electrical, thermoelectric, and vibronic properties. To that end, we introduce here the semiconducting vdW-material alpha-germanium(II) sulfide (GeS) as an intriguing candidate. By employing THz nanospectroscopy supported by theoretical analysis, we provide a thorough characterization of the different in-plane hyperbolic and elliptical PhP modes in GeS. We find not only PhPs with long lifetimes (τ > 2 ps) and excellent THz light confinement (λ0/λ > 45) but also an intrinsic, phonon-induced anomalous dispersion as well as signatures of naturally occurring, substrate-mediated PhP canalization within a single GeS slab., Parts of this research were carried out at ELBE at the Helmholtz-Zentrum Dresden - Rossendorf e. V., a member of the Helmholtz Association. T.N., M.O., L.W., S.C.K., L.M.E., and T.V.A.G.O. acknowledge the financial support by the Bundesministerium für Bildung und Forschung (BMBF, Federal Ministry of Education and Research, Germany, Project Grant Nos. 05K16ODA, 05K16ODC, 05K19ODA, and 05K19ODB) and by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy through Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter - ct.qmat (EXC 2147, project-id 390858490). F.H. and L.M.E. gratefully acknowledge financial support by the DFG through the project CRC1415 (ID: 417590517). A.Y.N. acknowledges the Spanish Ministry of Science and Innovation (Grants MAT201788358-C3-3-R and PID2020-115221GB-C42) and the Basque Department of Education (Grant PIBA-2020-1- 0014). G.Á .-P. acknowledges support through the Severo Ochoa Program from the Government of the Principality of Asturias (Grant No. PA-20-PF-BP19-053). P.A.-G. acknowledges support from the European Research Council under starting grant No. 715496, 2DNANOPTICA and the Spanish Ministry of Science and Innovation (State Plan for Scientific and Technical Research and Innovation Grant No. PID2019- 111156GB-I00). We are grateful for the fruitful discussions with Flávio H. Feres (Laboratório Nacional de Luz Síncrotron, Brazil).
- Published
- 2022