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Ebad-Allah J, Rojewski S, Vöst M, Eickerling G, Scherer W, Uykur E, Sankar R, Varrassi L, Franchini C, Ahn KH, Kuneš J, Kuntscher CA. Pressure-Induced Excitations in the Out-of-Plane Optical Response of the Nodal-Line Semimetal ZrSiS. Phys Rev Lett 2021; 127:076402. [PMID: 34459638 DOI: 10.1103/physrevlett.127.076402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Accepted: 06/17/2021] [Indexed: 06/13/2023]
Abstract
The anisotropic optical response of the layered, nodal-line semimetal ZrSiS at ambient and high pressure is investigated by frequency-dependent reflectivity measurements for the polarization along and perpendicular to the layers. The highly anisotropic optical conductivity is in very good agreement with results from density-functional theory calculations and confirms the anisotropic character of ZrSiS. Whereas the in-plane optical conductivity shows only modest pressure-induced changes, we found strong effects on the out-of-plane optical conductivity spectrum of ZrSiS, with the appearance of two prominent excitations. These pronounced pressure-induced effects can neither be attributed to a structural phase transition according to our single-crystal x-ray diffraction measurements, nor can they be explained by electronic correlation and electron-hole pairing effects, as revealed by theoretical calculations. Our findings are discussed in the context of the recently proposed excitonic insulator phase in ZrSiS.
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Affiliation(s)
- J Ebad-Allah
- Experimentalphysik II, University of Augsburg, 86159 Augsburg, Germany
- Department of Physics, Tanta University, 31527 Tanta, Egypt
| | - S Rojewski
- Experimentalphysik II, University of Augsburg, 86159 Augsburg, Germany
| | - M Vöst
- Chair of Chemical Physics and Materials Science, Institute of Physics, University of Augsburg, 86159 Augsburg, Germany
| | - G Eickerling
- Chair of Chemical Physics and Materials Science, Institute of Physics, University of Augsburg, 86159 Augsburg, Germany
| | - W Scherer
- Chair of Chemical Physics and Materials Science, Institute of Physics, University of Augsburg, 86159 Augsburg, Germany
| | - E Uykur
- 1. Physikalisches Institut, Universität Stuttgart, 70569 Stuttgart, Germany
| | - Raman Sankar
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
| | - L Varrassi
- Department of Physics and Astronomy, Alma Mater Studiorum-Università di Bologna, Bologna 40127, Italy
| | - C Franchini
- Department of Physics and Astronomy, Alma Mater Studiorum-Università di Bologna, Bologna 40127, Italy
- University of Vienna, Faculty of Physics and Center for Computational Materials Science, 1090 Vienna, Austria
| | - K-H Ahn
- Institute of Solid State Physics, TU Wien, 1020 Vienna, Austria
- Institute of Physics, The Czech Academy of Sciences, 16200 Praha, Czechia
| | - J Kuneš
- Institute of Solid State Physics, TU Wien, 1020 Vienna, Austria
- Institute of Physics, The Czech Academy of Sciences, 18221 Praha, Czechia
| | - C A Kuntscher
- Experimentalphysik II, University of Augsburg, 86159 Augsburg, Germany
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Ebad-Allah J, Baldassarre L, Sing M, Claessen R, Brabers VAM, Kuntscher CA. Polaron physics and crossover transition in magnetite probed by pressure-dependent infrared spectroscopy. J Phys Condens Matter 2013; 25:035602. [PMID: 23221151 DOI: 10.1088/0953-8984/25/3/035602] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The optical properties of magnetite at room temperature were studied by infrared reflectivity measurements as a function of pressure up to 8 GPa. The optical conductivity spectrum consists of a Drude term, two sharp phonon modes, a far-infrared band at around 600 cm(-1) and a pronounced mid-infrared absorption band. With increasing pressure both absorption bands shift to lower frequencies and the phonon modes harden in a linear fashion. Based on the shape of the MIR band, the temperature dependence of the dc transport data, and the occurrence of the far-infrared band in the optical conductivity spectrum, the polaronic coupling strength in magnetite at room temperature should be classified as intermediate. For the lower energy phonon mode an abrupt increase of the linear pressure coefficient occurs at around 6 GPa, which could be attributed to minor alterations of the charge distribution among the different Fe sites.
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Affiliation(s)
- J Ebad-Allah
- Experimentalphysik 2, Universität Augsburg, D-86135 Augsburg, Germany
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