Two-dimensional quadratic double Weyl semimetal

TL;DR

This paper predicts a stable two-dimensional quadratic double Weyl semimetal in Si/Bi heterostructures, revealing its topological phase transitions under strain and symmetry breaking, based on symmetry analysis and first-principles calculations.

Contribution

It introduces the first prediction of a 2D quadratic double Weyl semimetal in a Si/Bi heterostructure, exploring its stability and topological phase transitions.

Findings

Stable under compressive strain up to 6.64%

Transitions to trivial semimetal with increased strain

Can become quantum spin Hall or valley Hall insulator by symmetry breaking

Abstract

Unconventional Weyl semimetals have attracted intensive research interest in condensed matter physics and materials science, but they are very rare in two dimensions. In this work, based on symmetry analysis and the first-principles electronic structure calculations, we predict that the Si/Bi van der Waals heterostructure is a two-dimensional unconventional quadratic double Weyl semimetal with strong spin-orbit coupling (SOC). Although unprotected by the C3v double group symmetry of the heterostructure, the two-dimensional quadratic double Weyl semimetal is stable for compressive strains up to 6.64%. The system transforms into a trivial semimetal with further increasing strain, where the phase boundary is a two-dimensional triple degenerate semimetal state. Furthermore, the Kane-Mele tight-binding model calculations show that the quadratic double Weyl phase is derived from the competition between the Rashba SOC and the proximity-effect-enhanced intrinsic SOC. On the other hand, by breaking mirror symmetry, the quadratic double Weyl semimetal transforms into a quantum spin Hall insulator as well as a quantum valley Hall insulator phase. Thus, the Si/Bi heterostructure is an excellent platform for studying the exotic physics of two-dimensional double Weyl semimetal and other novel topological phases.