Detection of nontrivial topology driven by charge density wave in a semi-Dirac metal

TL;DR

This study investigates how charge density waves induce nontrivial topological phases in a semi-Dirac metal, revealing a correlation-driven topological transition with observable transport signatures and chiral metallic states.

Contribution

It uncovers a novel correlation-driven topological transition in a semi-Dirac metal, linking charge density waves, symmetry breaking, and Berry curvature effects through combined experimental and first-principles analysis.

Findings

Large planar Hall signals in the CDW phase

Identification of a chiral metallic phase with broken inversion symmetry

Correlation between charge localization and topological properties

Abstract

The presence of electron correlations in a system with topological order can lead to exotic ground states. Considering single crystals of LaAgSb2 which has a square net crystal structure, one finds multiple charge density wave transitions (CDW) as the temperature is lowered. We find large planar Hall (PHE) signals in the CDW phase, which are still finite in the high temperature phase though they change sign. Optimising the structure within first-principles calculations, one finds an unusual chiral metallic phase. This is because as the temperature is lowered, the electrons on the Ag atoms get more localized, leading to stronger repulsions between electrons associated with atoms on different layers. This leads to successive layers sliding with respect to each other, thereby stabilising a chiral structure in which inversion symmetry is also broken. The large Berry curvature associated with the low temperature structure explains the low temperature PHE. At high temperature the PHE arises from the changes induced in the tilted Dirac cone in a magnetic field. Our work represents a route towards detecting and understanding the mechanism in a correlation driven topological transition through electron transport measurements, complemented by ab-initio electronic structure calculations.