Infrared spectroscopic studies of the topological properties in CaMnSb2

TL;DR

This study uses infrared spectroscopy and theoretical calculations to investigate the topological properties of CaMnSb2, revealing low carrier density, complex optical features, and trivial surface states contrary to expectations for a topological material.

Contribution

It provides the first detailed infrared spectroscopic analysis of CaMnSb2 and combines it with first-principles calculations to clarify its topological nature and electronic structure.

Findings

Low carrier density indicated by plasma edge and Drude component.

Absence of Dirac fermion optical response in low-temperature conductivity.

Identification of interband transition peaks matching theoretical predictions.

Abstract

We present temperature-dependent infrared spectroscopic studies of CaMnSb2, a proposed threedimensional topological material. The low plasma edge in the reflectivity spectrum and small Drude component in the optical conductivity indicate a very low carrier density. The low-frequency optical conductivity is well described by the superposition of a narrow and a broad Drude terms. Several linear components have been observed in the low-temperature optical conductivity, but none of them extrapolates to the origin, at odds with the optical response expected for three-dimensional Dirac fermions. A series of absorption peaks have been resolved in the high-frequency optical conductivity. The energy of these peaks agrees well with the interband transitions expected for the band structures from first-principles calculations. Intriguingly, the lowest band gap increases with decreasing temperature, mimic the temperature evolution of inverted bands. Furthermore, our theoretical calculations demonstrate the existence of weak coupling between two Sb-chains layers results in the topological trivial surface states in CaMnSb2.