Optical conductivity of the Weyl semimetal NbP

TL;DR

This study investigates the optical properties of NbP, a Weyl semimetal, revealing details about its electronic transitions, phonon modes, and scattering rates across a broad spectral range and temperature spectrum.

Contribution

First comprehensive optical analysis of NbP linking experimental data with theoretical interband transition calculations.

Findings

Dominant interband transitions involve spin-orbit split bands below 100 meV.

Low-temperature scattering rate indicates very long momentum relaxation lengths (~0.5 μm).

Identification of phonon modes and their contribution to optical response.

Abstract

The optical properties of (001)-oriented NbP single crystals have been studied in a wide spectral range from 6 meV to 3 eV from room temperature down to 10 K. The itinerant carriers lead to a Drude-like contribution to the optical response; we can further identify two pronounced phonon modes and interband transitions starting already at rather low frequencies. By comparing our experimental findings to the calculated interband optical conductivity, we can assign the features observed in the measured conductivity to certain interband transitions. In particular, we find that transitions between the electronic bands spilt by spin-orbit coupling dominate the interband conductivity of NbP below 100 meV. At low temperatures, the momentum-relaxing scattering rate of the itinerant carriers in NbP is very small, leading to macroscopic characteristic length scales of the momentum relaxation of approximately 0.5 $\mu$m.