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激子绝缘体

Exciton insulators

  • 摘要: 激子绝缘体是20世纪60年代初由诺贝尔物理学奖获得者莫特提出的一种新物相。众所周知,激子是固态系统中最典型的集体激发之一,简单地可视为电子—空穴由于库仑相互作用而形成的束缚对。在常规绝缘体或半导体材料中,单粒子能隙远大于激子束缚能。而在某些特殊的材料体系,如窄能隙半导体和二维材料中,激子的束缚能可能大于体系的单粒子能隙,因此体系内会自发形成大量的激子,进入激子绝缘体相。激子绝缘体是体系的基态,低浓度下激子可视为组合玻色子,在低温下会形成宏观相干态——激子玻色—爱因斯坦凝聚。文章简要地回顾了激子绝缘体的发展历史,并介绍了激子绝缘体、玻色—爱因斯坦凝聚和自旋超流的最新进展。

     

    Abstract: An excitonic insulator is a new quantum phase proposed by the Nobel Prize winner in physics Nevill Mott in the early 1960s. It is well known that excitons are bound pairs formed by electron-hole Coulomb interaction in insulator and semiconductor systems where, traditionally, the single-particle energy gap is much larger than the exciton binding energy. However, in some specific materials, such as narrow-gap semiconductors and two-dimensional materials, this is reversed and a large number of excitons are spontaneously formed in the system, which becomes an exciton insulator and is the ground state. At low concentrations, excitons can be regarded as composite bosons, a macroscopic quantum coherent phase, thus an exciton Bose-Einstein condensate can be observed at low temperatures. This paper briefly reviews the history of exciton insulators, as well as recent progresses on exciton insulator phases and spin superfluidity.

     

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