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Symmetry-enforced fourfold degenerate phonons in noncentrosymmetric space groups. | LitMetric

Symmetry-enforced fourfold degenerate phonons in noncentrosymmetric space groups.

J Phys Condens Matter

Hunan Provincial Key laboratory of Thin Film Materials and Devices, School of Material Sciences and Engineering, Xiangtan University, Xiangtan 411105, People's Republic of China.

Published: January 2024

AI Article Synopsis

  • - The study focuses on understanding fourfold-degenerate (FD) phonons, which have unique properties due to their topological charge and boundary states, particularly in noncentrosymmetric crystal structures.
  • - Researchers classified the mechanisms generating FD phonons into two groups based on symmetry principles: one relies on little cogroup operations, while the other involves threefold rotation, mirror, and time-reversal symmetries; linear band dispersions are expected for the first group and quadratic for the second.
  • - The paper identifies K2MgO and Na4SnSe as materials correlated with the two FD phonon categories, aiming to enhance knowledge of FD phonon formation and provide practical examples for experimental observation in specific crystalline systems.

Article Abstract

Multifold degenerate phonons have received much attention due to their nontrivial monopole topological charge and fascinating boundary states. Although Yurecently provides a comprehensive list of all potential nodal points for systems with specific space groups (SGs) (2022375). However, our understanding of the fundamental mechanisms that give rise to the formation of fourfold-degenerate (FD) phonons is still limited. In this paper, we have directed our research towards investigating the generation mechanism of these FD phonons in noncentrosymmetric SGs. Using symmetry arguments andk⋅pmodel analysis, we have classified them into two categories: the first origins from the commutation/anticommutation relation of the little cogroup operations, and the second associates to the combination of threefold rotation, mirror and time-reversal symmetries. Moreover, the band dispersions of the FD phonons in the first group are required to be linear, whereas the band dispersions of the FD phonons in the second category may be quadratic. On the basis of first-principles calculations, we propose that K2MgOand Na4SnSeare representative candidates for the two categories, respectively. Furthermore, for each SG with fourfold degenerate phonons, we propose corresponding materials that must host the FD points. Our work not only deepens our understanding of the mechanisms underlying the formation of these FD phonons, but it also proposes practical materials for observing FD phonons in crystalline systems without inversion symmetry.

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Source
http://dx.doi.org/10.1088/1361-648X/ad1bf7DOI Listing

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