Two-dimensional Dirac Semimetals without Inversion Symmetry

TL;DR

This paper demonstrates that stable two-dimensional Dirac semimetals can exist without inversion symmetry, featuring nonzero Berry curvature and edge states, expanding the understanding of 2D topological semimetals and their potential transport phenomena.

Contribution

It reveals the existence of 2D Dirac points without inversion symmetry using theoretical models and first-principles calculations, and identifies a family of such materials.

Findings

2D Dirac points can survive without inversion symmetry.

Identified a family of ideal 2D Dirac semimetals with nonzero Berry curvature.

Edge states are present and terminate at Dirac points.

Abstract

Realizing stable two-dimensional (2D) Dirac points against spin-orbit coupling (SOC) has attracted much attention because it provides a platform to study the unique transport properties. In previous work, Young and Kane [Phys. Rev. Lett. \textbf{115}, 126803 (2015)] proposed stable 2D Dirac points with SOC, in which the Berry curvature and edge states vanish due to the coexistence of inversion and time-reversal symmetries. Herein, using the tight-binding model and k$\cdot$p effective Hamiltonian, we present that 2D Dirac points can survive in the presence of SOC without inversion symmetry. Such 2D Dirac semimetals possess nonzero Berry curvature near the crossing nodes, and two edge states are terminated at one pair of Dirac points. In addition, according to symmetry arguments and high-throughput first-principles calculations, we identify a family of ideal 2D Dirac semimetals, which has nonzero Berry curvature in the vicinity of Dirac points and visible edge states, thus facilitating the experimental observations. Our work shows that 2D Dirac points can emerge without inversion symmetry, which not only enriches the classification of 2D topological semimetals but also provides a promising avenue to observe exotic transport phenomena beyond graphene, e.g., nonlinear Hall effect.