Robust Tunable Large-Gap Quantum Spin Hall States in Monolayer Cu 2 S on Insulating Substrates.

Quantum spin Hall (QSH) insulators with large band gaps and dissipationless edge states are of both technological and scientific interest. Although numerous two-dimensional (2D) systems have been predicted to host the QSH phase, very few of them harbor large band gaps and retain their nontrivial band topology when they are deposited on substrates. Here, based on a first-principles analysis with hybrid functional calculations, we investigated the electronic and topological properties of inversion-asymmetric monolayer copper sulfide (Cu 2 S). Interestingly, we found that monolayer Cu 2 S possesses an intrinsic QSH phase, Rashba spin splitting, and a large band gap of 220 meV that is suitable for room-temperature applications. Most importantly, we constructed heterostructures of a Cu 2 S film on PtTe 2 , h-BN, and Cu(111) substrates and found that the topological properties remain preserved upon an interface with these substrates. Our findings suggest Cu 2 S as a possible platform to realize inversion-asymmetric QSH insulators with potential applications in low-dissipation electronic devices.