Optical conductivity and superconductivity in LaSb$_2$

TL;DR

This study investigates LaSb$_2$'s optical, magnetic, and resistive properties, revealing no charge density wave formation, magnetoresistance due to scattering, and a pressure-stabilized, fragile superconducting state with variable transition temperatures.

Contribution

It provides new insights into LaSb$_2$'s superconducting behavior and magnetoresistance mechanisms, including the effects of pressure and sample variability.

Findings

No charge density wave detected above 20 K.

Magnetoresistance attributed to scattering rate changes.

Superconducting transition observed at 2.5 K, stabilized by pressure.

Abstract

We have measured the resistivity, optical conductivity, and magnetic susceptibility of LaSb$_2$ to search for clues as to the cause of the extraordinarily large linear magnetoresistance and to explore the properties of the superconducting state. We find no evidence in the optical conductivity for the formation of a charge density wave state above 20 K despite the highly layered crystal structure. In addition, only small changes to the optical reflectivity with magnetic field are observed indicating that the MR is due to scattering rate, not charge density, variations with field. Although a superconducting ground state was previously reported below a critical temperature of 0.4 K, we observe, at ambient pressure, a fragile superconducting transition with an onset at 2.5 K. In crystalline samples, we find a high degree of variability with a minority of samples displaying a full Meissner fraction below 0.2 K and fluctuations apparent up to 2.5 K. The application of pressure stabilizes the superconducting transition and reduces the anisotropy of the superconducting phase.