Substrate-induced magnetism and topological phase transition in silicene

TL;DR

This study demonstrates how silicene on CeO2 substrate exhibits induced magnetism and a topological phase transition, impacting its potential for spintronic applications, and proposes a structure to preserve its quantum spin Hall state.

Contribution

It reveals substrate-induced magnetism and topological phase transition in silicene, and introduces a sandwich structure to maintain its quantum spin Hall effect.

Findings

Magnetism appears in silicene on CeO2 due to covalent bonding.

A topological phase transition to a band insulator occurs regardless of bonding type.

Weak substrate interactions can destroy silicene's quantum spin Hall effect.

Abstract

Silicene has shown great application potential as a versatile material for nanoelectronics, particularly promising as building block for spintronic applications. Unfortunately, despite its intriguing properties, such as relatively large spin-orbit interactions, one of the biggest hurdles for silicene to be useful as a host spintronic material is the lack of magnetism or the topological phase transition owing to the silicene-substrate interactions, which influence its fundamental properties and has yet to be fully explored. Here, we show that when silicene is grown on CeO2 substrate, an appreciable robust magnetic moment appears in silicene covalently bonded to CeO2 (111), while a topological phase transition to a band insulator occurs regardless of van der Waals (vdWs) interaction or covalent bonding interaction at interface. The induced magnetism of silicene is due to the breaking of Si-Si {\pi}-bonding, also resulting in trivial topological phase. The silicene-substrate interaction, even weak vdWs force (equivalent to an electric field), can destroy quantum spin Hall effect (QSHE) of silicene. We propose a viable strategy --- constructing inverse symmetrical sandwich structure (protective layer/silicene/substrate) --- to preserve quantum spin Hall (QSH) state of silicene in weak vdWs interaction system. This work takes a critical step towards fundamental physics and realistic applications of silicene-based spintronic devices.