Large-Gap Quantum Spin Hall Insulators in Tin Films

TLDR

Large-gap quantum spin Hall insulators are sought for both fundamental and practical reasons, and tuning their states remains a key challenge. The QSH effect in tin films arises from band inversion at the Γ point, analogous to HgTe quantum wells. First‑principles calculations show two‑dimensional tin films are QSH insulators with a 0.3 eV bulk gap, tunable by chemical functionalization, strain, and surface magnetic doping that could yield a quantum anomalous Hall effect.

Abstract

The search for large-gap quantum spin Hall (QSH) insulators and effective approaches to tune QSH states is important for both fundamental and practical interests. Based on first-principles calculations we find two-dimensional tin films are QSH insulators with sizable bulk gaps of 0.3 eV, sufficiently large for practical applications at room temperature. These QSH states can be effectively tuned by chemical functionalization and by external strain. The mechanism for the QSH effect in this system is band inversion at the Γ point, similar to the case of a HgTe quantum well. With surface doping of magnetic elements, the quantum anomalous Hall effect could also be realized.