Bond-breaking Induced Lifshitz Transition in Robust Dirac Semimetal $\mathbf{VAl_3}$

TL;DR

This study demonstrates that the Dirac electrons in VAl3 are exceptionally robust against chemical doping, with a Lifshitz transition occurring at high Ti substitution levels due to bond breaking, revealing a new way to find stable topological materials.

Contribution

The paper reveals that the topological Dirac electrons in VAl3 are protected by V-Al bonds and remain stable despite significant chemical doping, identifying a bond-breaking Lifshitz transition.

Findings

Dirac electrons in VAl3 are robust against Ti doping.

A Lifshitz transition occurs at x=0.35 in V_{1-x}Ti_xAl_3.

Bond breaking correlates with the loss of Dirac electron protection.

Abstract

Topological electrons in semimetals are usually vulnerable to chemical doping and environment change, which restricts their potential application in future electronic devices. In this paper we report that the type-II Dirac semimetal $\mathbf{VAl_3}$ hosts exceptional, robust topological electrons which can tolerate extreme change of chemical composition. The Dirac electrons remain intact even after a substantial part of V atoms have been replaced in the $\mathbf{V_{1-x}Ti_xAl_3}$ solid solutions. This Dirac semimetal state ends at $x=0.35$ where a Lifshitz transition to $p$-type trivial metal occurs. The V-Al bond is completely broken in this transition as long as the bonding orbitals are fully depopulated by the holes donated from Ti substitution. In other words, the Dirac electrons in $\mathbf{VAl_3}$ are protected by the V-Al bond whose molecular orbital is their bonding gravity center. Our understanding on the interrelations among electron count, chemical bond and electronic properties in topological semimetals suggests a rational approach to search robust, chemical-bond-protected topological materials.