Pressure Effect on Band Inversion in AECd2As2

TL;DR

This study investigates how applying pressure affects the electronic band structure and induces topological phase transitions in non-magnetic AECd2As2 compounds using density functional theory.

Contribution

It reveals pressure-induced band inversion and Dirac points in AECd2As2, expanding understanding of topological states in these materials.

Findings

Pressure reduces band gap in AECd2As2 compounds.

Band inversion occurs under negative pressure, leading to Dirac points.

Topological surface states confirmed by Fermi arcs.

Abstract

Recent studies have predicted that magnetic EuCd2As2 can host several different topological states depending on its magnetic order, including a single pair of Weyl points. Here we report on the bulk properties and band inversion induced by pressure in the non-magnetic analogs AECd2As2 (AE = Ca, Sr, Ba) as studied with density functional theory calculations. Under ambient pressure we find these compounds are narrow band gap semiconductors, in agreement with experiment. The size of the band gap is dictated by both the increasing ionicity across the AE series which tends to increase the band gap, as well as the larger nearest neighbor Cd-As distance from increasing atomic size which can decrease the band gap because the conduction band edge is an anti-bonding state derived mostly from Cd 5s orbitals. The combination of these two competing effects results in a non-monotonic change of the band gap size across the AE series with SrCd2As2 having the smallest band gap among the three compounds. The application of negative pressure reduces this band gap and causes the band inversion between the Cd 5s and As 4p orbitals along the ${\Gamma}$-A direction to induce a pair of Dirac points. The topological nature of the Dirac points is then confirmed by finding the closed Fermi arcs on the (10-10) surface.