Magnetotransport properties of the layered CaAl2Si2 semimetal hosting multiple nontrivial topological states

TL;DR

This study investigates the magnetotransport properties and topological states of CaAl2Si2, revealing multiple topological phases including nodal-line, Dirac points, and topological insulator states influenced by spin-orbit coupling.

Contribution

It provides the first comprehensive analysis combining experiments and ab initio calculations to identify multiple topological states in CaAl2Si2, a layered semimetal.

Findings

Transport properties explained by a two-band model

Identification of a single quantum oscillation frequency

Prediction of topological nodal-line and Dirac states influenced by SOC

Abstract

Combination of different nontrivial topological states in a single material is capable of realizing multiple functionalities and exotic physics, but such materials are still very sparse. We report herein the results of magnetotransport measurements and ab initio calculations on single crystalline CaAl2Si2 semimetal. The transport properties could be well understood in connection with the two-band model, agreeing well with the theoretical calculations indicating four main sheets of Fermi surface consisting of three hole pockets centered at the {\Gamma} point and one electron pocket centered at the M point in the Brillouin zone. The single fundamental frequency imposed in the quantum oscillations of magnetoresistance corresponds to the electron Fermi pocket. Without spin-orbit coupling (SOC), the ab initio calculations suggest CaAl2Si2 as a system hosting a topological nodal-line setting around the {\Gamma} point in the Brillouin zone close to the Fermi level. Once including the SOC, the fragile nodal-line will be gapped and a pair of Dirac points emerge along the high symmetric {\Gamma}-A direction, which is about 1.22 eV below the Fermi level. The SOC can also induce a topological insulator state along the {\Gamma}-A direction with a gap of about 3 meV. The results demonstrate CaAl2Si2 as an excellent platform for the study of novel topological physics with multiple topological states.