Optical conductivity of topological semimetal Nb$_{2n+1}$Si$_n$Te$_{4n+2}$

TL;DR

This paper analyzes the optical conductivity of Nb$_{2n+1}$Si$_n$Te$_{4n+2}$, revealing anisotropic Drude weight and linear frequency dependence in interband conductivity, with finite-temperature effects considered.

Contribution

It provides an analytical study of optical conductivity in a layered topological semimetal, highlighting anisotropic Drude weight and frequency dependence.

Findings

Drude weight is finite along the nodal-line at charge neutrality.

Interband optical conductivity shows linear frequency dependence in both directions.

Finite-temperature corrections do not significantly alter zero-temperature results.

Abstract

We study the linear optical conductivity of the Nb$_{2n+1}$Si$_n$Te$_{4n+2}$ family of layered van der Waals materials, which has recently gained considerable attention owing to its dimensionality-tunable electronic structure with a quasi-one-dimensional nodal-line state. At zero temperature, we analytically show that the Drude weight exhibits strong anisotropy: along the nodal-line direction it is finite at charge neutrality, whereas in the transverse direction it vanishes quadratically with Fermi energy. On the other hand, the interband optical conductivity exhibits the same linear frequency dependence along both the longitudinal and transverse directions, with only a direction-dependent slope in the low-frequency regime. We further analyze the leading finite-temperature corrections to the intraband and interband optical conductivities, showing that the zero-temperature results remain valid up to experimentally relevant temperatures.