Modification of the Hybridization Gap by Twisted Stacking of Quintuple Layers in a Three-Dimensional Topological Insulator Thin Film

Twisting the stacking of layered materials leads to rich new physics. A three-dimensional topological insulator film hosts two-dimensional gapless Dirac electrons on top and bottom surfaces, which, when the film is below some critical thickness, will hybridize and open a gap in the surface state structure. The hybridization gap can be tuned by various parameters such as film thickness and inversion symmetry, according to the literature. The three-dimensional strong topological insulator Bi(Sb)Se(Te) family has layered structures composed of quintuple layers(QLs) stacked together by van der Waals interaction. Here we successfully grow twistedly stacked Sb_2Te_3 QLs and investigate the effect of twist angels on the hybridization gaps below the thickness limit. It is found that the hybridization gap can be tuned for films of three QLs, which may lead to quantum spin Hall states.Signatures of gap-closing are found in 3-QL films. The successful in situ application of this approach opens a new route to search for exotic physics in topological insulators.

后现代视角下的文化认同——重读任璧莲小说《典型美国人》

被称为华裔美国作家“四人帮”之一的任璧莲以其早期代表作《典型美国人》响誉美国文坛。小说以其极具反讽意味的标题,诙谐的笔调,以及对“熔炉”语境中“典型美国人”的质疑和颠覆,开辟一片少数族裔文学的新天地。任璧莲极具后现代性的文化认同观使其作品和“身份困惑”主题有别于其他华裔作家。其作品反映的文化认同的“杂和性”和“流变性”对全球化语境下的“文化认同”创造了更广阔的发展空间。