Switching of topological phase transition from semiconductor to ideal Weyl states in Cu$_2$SnSe$_3$ family of materials

TL;DR

This paper introduces a novel, symmetry-independent topological phase transition mechanism in Cu$_2$SnSe$_3$ materials, transforming semiconductors into ideal Weyl semimetals via doping-induced bandgap closure and spin-orbit coupling enhancement.

Contribution

It proposes a new TPT mechanism that does not rely on symmetry breaking, demonstrated through first-principles calculations in Cu$_2$SnSe$_3$ family.

Findings

Weyl points emerge near the Fermi level in doped Cu$_2$SnSe$_3$

Bulk Fermi surface becomes nearly point-like

Surface Fermi surface consists solely of Fermi arcs

Abstract

The exploration of topological phase transition (TPT) mechanisms constitutes a central theme in quantum materials research. Conventionally, transitions between Weyl semimetals (WSMs) and other topological states rely on the breaking of time-reversal symmetry (TRS) or precise manipulation of lattice symmetry, thus constraints the available control strategies and restrict the scope of viable material systems. In this work, we propose a novel mechanism for TPT that operates without TRS breaking or lattice symmetry modification: a class of semiconductors can be directly transformed into an ideal WSM via bandgap closure. This transition is driven by chemical doping, which simultaneously modulates the band gap and enhances spin-orbit coupling (SOC), leading to band inversion between the valence and conduction bands and thereby triggering the TPT. Using first-principles calculations, we demonstrate the feasibility of this mechanism in the Cu$_2$SnSe$_3$ family of materials, where two pairs of Weyl points emerge with energies extremely close to the Fermi level. The bulk Fermi surface becomes nearly point-like, while the surface Fermi surface consists exclusively of Fermi arcs. This symmetry-independent mechanism bypasses the constraints of conventional symmetry-based engineering, and also offers an ideal platform for probing the anomalous transport properties of WSMs.