Multiple fermionic states with clear nontrivial surface signature in CsCl-type compound ErAs

Abstract

Topological semimetals with hosting multiple types of fermions has attracted considerable attention currently. For such materials, however, the signatures for different fermions such as the nontrivial surface states are usually tangled together, which troubles their experimental detections. Here, by using the first-principles calculation, we propose that the CsCl-type compound ErAs host multiple fermionic states near the Fermi level. Most importantly, all these fermionic states can exhibit clear surface signature. When spin–orbit coupling (SOC) is not included, ErAs totally shows three pairs of triply degenerate nodal points (TDNPs) and six nodal lines. Especially, three of the nodal lines host both type-I and type-II band crossings, namely hybrid nodal lines. The TDNPs and nodal lines in ErAs are characterized with clear Fermi arcs and drumhead surface states. After considering SOC, it emerges three pairs of Dirac points in ErAs. These Dirac points can also show clear Fermi arc surface states, which strongly favors their experimental detections.