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Phonon properties and unconventional heat transfer in a quasi-two-dimensional Bi.sub.2./sub.O.sub.2./sub.Se crystal
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SYSNO ASEP 0627726 Document Type J - Journal Article R&D Document Type Journal Article Subsidiary J Článek ve SCOPUS Title Phonon properties and unconventional heat transfer in a quasi-two-dimensional Bi2O2Se crystal Author(s) Zich, Jan (FZU-D) ORCID
Sojka, A. (CZ)
Levinský, Petr (FZU-D) RID, ORCID
Míšek, Martin (FZU-D) RID, ORCID
Ahn, Kyo-Hoon (FZU-D) ORCID, RID
Navrátil, J. (CZ)
Hejtmánek, Jiří (FZU-D) RID, ORCID
Knížek, Karel (FZU-D) RID, ORCID
Holý, V. (CZ)
Nuzhnyy, Dmitry (FZU-D) RID, ORCID
Borodavka, Fedir (FZU-D) RID, ORCID
Kamba, Stanislav (FZU-D) RID, ORCID, SAI
Drašar, Č. (CZ)Number of authors 13 Article number 054603 Source Title Physical Review Materials. - : American Physical Society - ISSN 2475-9953
Roč. 9, č. 5 (2025)Number of pages 9 s. Language eng - English Country US - United States Keywords quasi-2D semiconductors ; infrared and Raman spectroscopy ; density functional theory calculations ; heat capacity ; heat conductivity Subject RIV BM - Solid Matter Physics ; Magnetism OECD category Condensed matter physics (including formerly solid state physics, supercond.) R&D Projects EH22_008/0004594 GA MŠMT - Ministry of Education, Youth and Sports (MEYS) GA22-05919S GA ČR - Czech Science Foundation (CSF) Method of publishing Limited access Institutional support FZU-D - RVO:68378271 EID SCOPUS 105004739038 DOI https://doi.org/10.1103/PhysRevMaterials.9.054603 Annotation Bi2O2Se belongs to a group of quasi-2D semiconductors that can replace silicon in future high-speed/low-power electronics. However, the correlation between crystal/band structure and other physical properties still eludes understanding: carrier mobility increases non-intuitively with carrier concentration, the observed T2 temperature dependence of resistivity lacks explanation. Moreover, a very high relative out-of-plane permittivity of about 150 has been reported in the literature. A proper explanation for such a high permittivity is still lacking. We have performed infrared (IR) reflectivity and Raman scattering experiments on a large perfect single crystal with defined mosaicity, carrier concentration, and mobility. Five of the eight phonons allowed by factor group theory have been observed and their symmetries determined. The IR spectra show that the permittivity measured in the tetragonal plane is as high as εr≈500, and this high value is due to a strong polar phonon with a low frequency of ∼34 cm-1 (∼1 THz). Such an unusually high permittivity allows the screening of charge defects, leading to the observation of high electron mobility at low temperatures. It also allows effective modulation doping providing a platform for high-performance 2D electronics. DFT calculations suggest the existence of a very low-frequency acoustic phonon ∼14 cm-1 (∼0.4 THz). Both the low-frequency phonons cause anomalous phonon DOS, which is reflected in the unconventional temperature dependence of the heat capacity, Cp≈T3.5. The temperature-dependent, two-component group velocity is proposed to explain the unusual temperature dependence of the thermal conductivity, k≈T1.5. Workplace Institute of Physics Contact Kristina Potocká, potocka@fzu.cz, Tel.: 220 318 579 Year of Publishing 2026 Electronic address https://doi.org/10.1103/PhysRevMaterials.9.054603
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