Terahertz Spectroscopy and DFT Analysis of Phonon Dynamics of the Layered Van der Waals Semiconductor Nb3 X 8 (X = Cl, I)

Jangwon Kim; Youjin Lee; Young Woo Choi; Taek Sun Jung; Suhan Son; Jonghyeon Kim; Hyoung Joon Choi; Je-Geun Park; Jae Hoon Kim

doi:10.1021/acsomega.3c01019

Terahertz Spectroscopy and DFT Analysis of Phonon Dynamics of the Layered Van der Waals Semiconductor Nb₃ X ₈ (X = Cl, I)

ACS Omega. 2023 Apr 8;8(15):14190-14196. doi: 10.1021/acsomega.3c01019. eCollection 2023 Apr 18.

Authors

Jangwon Kim¹, Youjin Lee^{2

3}, Young Woo Choi¹, Taek Sun Jung¹, Suhan Son^{2

3}, Jonghyeon Kim¹, Hyoung Joon Choi¹, Je-Geun Park^{2

3}, Jae Hoon Kim¹

Affiliations

¹ Department of Physics, Yonsei University, Seoul 03722, Republic of Korea.
² Center for Quantum Materials, Seoul National University, Seoul 08826, Republic of Korea.
³ Department of Physics and Astronomy & Institute of Applied Physics, Seoul National University, Seoul 08826, Republic of Korea.

Abstract

We have conducted a terahertz spectroscopic study and a density functional theory analysis of the phonon dynamics of the layered van der Waals semiconductors Nb₃Cl₈ and Nb₃I₈. Several infrared-active phonon modes were observed in the terahertz region, and their frequencies were found to be in excellent agreement with our first-principles lattice dynamics calculations. For Nb₃Cl₈, the observed phonon spectra are consistent with a structural transition at 90 K from the high-temperature P3̅m1 phase to the low-temperature R3̅m phase. Also, our study confirmed that the structural and magnetic transitions were coupled in Nb₃Cl₈. For Nb₃I₈, which is nonmagnetic at and below room temperature, no significant temperature or magnetic field dependence was observed in the phonon spectra. Our study provides an intriguing connection between the structural properties and the paramagnetic-nonmagnetic transitions in Nb₃Cl₈ and Nb₃I₈.