Electronic band structure and surface states in Dirac semimetal LaAgSb$_{2}$

Abstract

LaAgSb$_{2}$ is a Dirac semimetal showing charge density wave (CDW) order. Previous ARPES results suggest the existence of the Dirac-cone-like structure in the vicinity of the Fermi level along the $\Gamma$-M direction [X. Shi et al., Phys. Rev. B 93, 081105(R) (2016)]. This paper is devoted to a complex analysis of the electronic band structure of LaAgSb$_{2}$ by means of angle-resolved photoemission spectroscopy (ARPES) and theoretical calculations within the direct ab initio method as well as tight binding model formulation. To investigate the possible surface states we performed the direct DFT slab calculation and the surface Green function calculation for the (001) surface. The appearance of the surface states, which depends strongly on surface, points to the conclusion that LaSb termination is realized in the cleaved crystals. Moreover, the surface states predicted by our calculations at the $\Gamma$ and $X$ points are found by ARPES. Nodal lines, which exist along X--R and M-A path due to crystal symmetry, are also observed experimentally. The calculations reveal another nodal lines, which originate from vanishing of spin-orbit coupling and are located at X-M-A-R plane at the Brillouin zone boundary. In addition, we analyze band structure along the $\Gamma$-M path to verify, whether Dirac surface states can be expected. Their appearance in this region is not confirmed.