锡烯的研究进展

Recent progress in the study of stanene

石墨烯研究的巨大成功推动了二维晶体材料研究领域的蓬勃发展,和碳同族的Ⅳ族元素组成的具有类石墨烯结构的二维晶体材料受到了广泛的关注,其中由锡元素组成的锡烯晶体由于其优异的物理特性成为研究的热点之一.理论计算表明锡烯是一种大能隙的量子自旋霍尔效应绝缘体,还能够转化为二维的拓扑超导体.锡烯晶体在电子无耗散输运、自旋流产生、高性能热电、光电器件、拓扑量子计算等方面都具有重要的潜在应用价值.本文针对最近几年来锡烯的研究进展进行简要的综述.首先简单描述为什么锡烯晶体具有特殊的物理特性,然后介绍锡烯理论研究的进展以及最近利用分子束外延技术在锡烯晶体薄膜制备方法取得的突破,最后对今后可能的实验研究方向和内容进行了展望.

Inspired by the successfully experimental realization of graphene, other ultrathin materials consisting of group-IV elements Si, Ge and Sn have been attracted plenty of interests due to their unprecedented electronic properties. Among them, two-dimensional low-buckled Sn-based stanene and its derivatives present novel quantum properties due to its large spin-orbital coupling, such as a quantum spin Hall insulating behaviour with a very large band gap, and the capability to support enhanced thermoelectric performance, topological superconductivity and the near-room-temperature quantum anomalous Hall effect and so on. Therefore, stanene shows the great application potentials in the dissipationless electric conduction at room temperature, high performance thermoelectricity, spintronics and topological quantum computation. This review will briefly introduce the recent progress in the study of stanene both in theory and in experiment. Firstly, we will discuss the main motivation on study of the stanene. Tin（Sn） is a heavy element and stanene has the low-buckled honeycomb-like crystal structure, which makes its spin-orbital coupling strong enough to realize a quantum spin Hall state with a large energy gap of about 0.1 eV. The large bulk gap makes stanene the excellent candidate to explore the topological quantum properties of a quantum spin Hall insulator above the cryogenic temperature. Secondly, we will briefly introduce the theoretical calculations or predictions of the crystal and electronic structures of stanene. First-principle calculations show that the honeycomb-like low-buckled crystal structure of two-dimensional stanene is stable and could be realized experimentally in principle. Due to the sp^3 orbitals in stanene, it has dangling bonds that can be modified by surface decoration. Long range ferromagnetic order, topological superconductivity and largely enhanced bulk energy gap（up to ~ 0.3 eV） can be achieved by proper surface decoration theoretically. Topological transition can also induced by hydrogen absorption. Thirdly, we will discuss the first experimental realization of the monolayer stanene films with low-buckled crystal structure using molecular beam epitaxy method on the Bi2Te3 single crystalline substrates, which brings the stanene to the real word and inspires more and more theoretical predictions. The crystal structure of epitaxial growth stanene was determined by scanning tunneling spectroscopy and its electronic structure was measured by angle-resolved photoemission spectroscopy. Due to the charge transfer between the epitaxial stanene and the Bi2Te3 substrate, stanene film on Bi2Te3 is not an insulator. It is hole-doped. At last, we will introduce some very recent theoretical works on how to improve stanene films beyond the current experimental achievements. Based on new proposals, new experiments could be done on the stanene films. For example, new substrate has been proposed by first-principle calculations to get high-quality stanene films with much larger area; other quantum orders such as ferromagnetism and superconductivity can be realized through surface decoration or electron doping, which can be tested using low-temperature scanning tunneling spectroscopy. Very low thermal conductivity was founded in theory in stanene, which is another very interesting experiment. Finally, new insulating substrates has been suggested by first-principle calculations to obtain insulating stanene films that can be used to study the electric transport properties of the topological one-dimensional edge states. More experiments could be carried out along this direction.