Degenerate line modes in the surface and bulk phonon spectra of orthorhombic NaMgF3perovskite
Publication Name
Applied Physics Letters
Abstract
Degenerate bulk-line phonon modes have been widely reported in various crystal system types; however, degenerate surface-line phonon modes have only been reported in monoclinic crystal systems, such as SnIP with space group P 2 / c (No. 13). Herein, we propose that degenerate surface-line phonon modes can also emerge in solids with orthorhombic structures. Based on first-principle calculations and symmetry analysis, we propose that orthorhombic NaMgF3 fluoroperovskite with space group Pnma (No. 62) is a material candidate with degenerate line states in both the bulk phonon mode and the (010) surface phonon mode. We discovered four closed nodal loops (two type-I and two hybrid-type) on the ky = 0 plane in the bulk phonon mode, all of which coexisted with Dirac points on the Z-U and X-U paths. Moreover, we discovered symmetry-projected doubly degenerate nodal lines along the X ¯ - U ¯ surface path in the (010) surface phonon mode. The proposed degenerate surface-line phonons in NaMgF3 is quite clean and protected by symmetries, which will aid future experimental detection.
Open Access Status
This publication is not available as open access
Volume
121
Issue
19
Article Number
192201
Funding Number
A2021202002
Funding Sponsor
Natural Science Foundation of Hebei Province