Topological Phases in Hydrogenated Group 13 Monolayers

Abstract

Nontrivial topology of Dirac semimetals, Weyl semimetals, and nodal line semimetals (NLSMs) is delineated by the novel band crossings near the Fermi level in the bulk and the appearance of exotic surface states. Among them, NLSMs have gained immense interest because of the formation of a one-dimensional nodal ring near the Fermi level. Using density functional theory calculations and an effective two-band k•p model, we report that a two-dimensional (2D) NLSM phase can be hosted on hydrogen-passivated gallenene (gallenane) and on other group 13 elements, without inclusion of spin−orbit coupling (SOC). NLSM in these 2D systems is protected by the presence of crystalline symmetry along with inversion symmetry and time-reversal symmetry. In the presence of SOC, aluminane preserves its topological NLSM phase, while in other hydrogenated group 13 monolayers, a gap opens at the nodal point because of relatively stronger SOC effect. On applying tensile strain along with the inclusion of SOC, gallenane evolves into a quantum spin Hall insulator with an indirect band gap of 28 meV. The appearance of long-range dissipationless linearly dispersive helical edge states and a large gap in gallenane makes it promising for room-temperature spintronic applications.

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