Simulations point to new materials for room-temperature quantum spin Hall insulators

Topological electronics leverage quantum mechanics in the hopes of greatly increasing device efficiency. One such technology, quantum spin Hall (QSH) insulators, resist electric currents in bulk by separating the valence and conduction bands with an energy gap, only allowing electric currents at the edge. Many QSH insulators require a large band gap to stabilize the edge current against the influence of room-temperature thermally activated bulk carriers and often only work at ultralow temperatures. New work provides a direction for finding the right material to make room-temperature QSH insulators.

Authors of work published in the Journal of Applied Physics have predicted using first-principle simulations that honeycombs of thallium antimonide (TlSb) have the capability of acting as QSH insulators at room temperature. According to their findings, methyl- and ethynyl-functionalized TlSb thin films not only exhibit a large band gap, but will also be able to withstand enough external strain to be robust in several applications.

The two functionalized TlSb monolayers the research team investigated, TlSb(CH₃)₂ and TlSb(C₂H)₂, had band gaps of 0.13 eV and 0.272 eV, respectively. They report that both types of thin films are able to maintain QSH phases over great ranges of strain, and with various configurations of methyl/ethynyl coverage, when grown on hBN.

The team said they hope their work will lead them to exploring how to synthesize these films and one day design and fabricate topological electronic devices based on them.

Source: “Robust large gap quantum spin Hall insulators in methyl and ethynyl functionalized TlSb buckled honeycombs,” by Qing Lu, Ran Ran, Yan Cheng, Busheng Wang, Zhao-Yi Zeng, and Xiang-Rong Chen, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5033999 .