Topological Aspect and Quantum Magnetoresistance of $\beta$-Ag$_2$Te

TL;DR

This paper demonstrates through first principles calculations that $eta$-Ag$_2$Te is a topological insulator with highly anisotropic Dirac surface states, providing insights into its unusual magnetoresistance behavior.

Contribution

It reveals that $eta$-Ag$_2$Te is a topological insulator with unique anisotropic Dirac surface states, expanding the class of known topological materials.

Findings

$eta$-Ag$_2$Te is a topological insulator with gapless surface states.

The Dirac cone in $eta$-Ag$_2$Te is highly anisotropic.

Fermi velocity varies significantly with crystal orientation.

Abstract

To explain the unusual non-saturating linear magnetoresistance observed in silver chalcogenides, the quantum scenario has been proposed based on the assumption of gapless linear energy spectrum. Here we show, by first principles calculations, that $\beta$-Ag$_2$Te with distorted anti-fluorite structure is in fact a topological insulator with gapless Dirac-type surface states. The characteristic feature of this new binary topological insulator is the highly anisotropic Dirac cone, in contrast to known examples, such as Bi$_2$Te$_3$ and Bi$_2$Se$_3$. The Fermi velocity varies an order of magnitude by rotating the crystal axis.