Origin of the structural phase transition at 130 K in BaNi$_2$As$_2$: a combined study of optical spectroscopy and band structure calculations

TL;DR

This study combines optical spectroscopy and band structure calculations to investigate the 130 K structural transition in BaNi$_2$As$_2$, revealing a reduction in conducting carriers linked to Fermi surface changes.

Contribution

It provides a detailed analysis of the electronic structure changes across the phase transition using combined experimental and theoretical methods.

Findings

BaNi$_2$As$_2$ is a good metal with high plasma frequency.

The phase transition causes a small reduction in conducting carriers.

The carrier reduction is due to removal of small Fermi surface sheets from specific bonding states.

Abstract

BaNi$_2$As$_2$ exhibits a first order structural transition at 130 K. Understanding this structural transition is a crucial step towards understanding the electronic properties of the material. We present a combined optical spectroscopy and band structure calculation study on the compound across the transition. The study reveals that BaNi$_2$As$_2$ is a good metal with a rather high plasma frequency. The phase transition leads to a small reduction of conducting carriers. We identify that this reduction is caused by the removal of several small Fermi surface sheets contributed dominantly from the As-As bonding and Ni-As antibonding states.