Unconventional superconducting transport in semiconductor Dirac materials

近年来，半导体狄拉克材料（SDM）引起了人们极大的兴趣，所述半导体狄拉克材料包括体窄禁带半导体（例如Bi 2 Se 3、Bi 2 Te 3、HgTe）及其异质结构（例如HgTe量子威尔斯阱）。Bi2Se3，Bi2Te3，HgTe和其他类似化合物的大块样品支持不寻常的表面电子态，模拟二维无质量狄拉克费米子的行为。的n型碲化汞量子威尔斯表现出更一般类型的狄拉克载流子，具有可调的有效质量和非平凡的带曲率。SDM与其他狄拉克材料（例如石墨烯）以及传统宽带半导体的定性区别在于，在SDM中，电荷载流子的特征在于明确定义的自旋螺旋度，即自旋和动量方向的锁定。大量的研究存在的自旋螺旋度的作用，电子输运中的SDM。然而，到目前为止，这个问题主要是在正常（即非超导）运输制度的研究。最近，第一次成功的实验在SDM的邻近效应和约瑟夫森效应已经出现，展现了他们的潜力，作为一种新型的超导弱连接。本论文的目标是研究自旋螺旋SDM弱连接中的超导输运，重点研究诱导p波超导性。p波超导性在凝聚态系统中是非常规的，引起了奇异的现象，如马约拉纳束缚态，可以在量子信息处理中发挥重要作用。这个项目涉及一个相关的，但几乎没有探索的现象-超导克莱因隧道-及其表现在各种介观SDM结构。超导克莱因隧道意味着保护超电流免受通常散射机制的影响，这在实践中可能有助于改善约瑟夫森结的输运特性。

Recent years have seen a splash of interest in semiconductor Dirac materials (SDMs) which include bulk narrow gap semiconductors (e.g. Bi2Se3, Bi2Te3, HgTe) and their heterostructures (e.g. HgTe quantum wells). Bulk samples of Bi2Se3, Bi2Te3, HgTe and other similar compounds support unusual surface electronic states that mimic the behavior of the two-dimensional massless Dirac fermions. The n-type HgTe quantum wells exhibit a more general type of Dirac carriers, with a tunable effective mass and nontrivial band curvature. What qualitatively distinguishes the SDMs from other Dirac materials (e.g. graphene) as well as from the conventional wide band semiconductors is the fact that in a SDM the charge carriers are characterized by a well-defined spin helicity, i.e. the locking of the spin and momentum directions. A large body of research exists on the role of the spin helicity in the electron transport in the SDMs. Until now, however, this issue has been investigated mainly in the normal (i.e. non-superconducting) transport regime. Very recently, first successful experiments on the proximity and Josephson effects in the SDMs have appeared, unfolding their potential as a new type of superconducting weak links. The objective of the present proposal is the theoretical investigation of the superconducting transport in spin-helical SDM weak links with the focus on induced p-wave superconductivity. The p-wave superconductivity is unconventional in condensed matter systems, giving rise to exotic phenomena such as Majorana bound states that could play an important role in quantum information processing. This project deals with a related, but barely explored phenomenon - superconducting Klein tunneling - and its manifestations in various mesoscopic SDM structures. The superconducting Klein tunneling implies protection of the supercurrent against usual scattering mechanisms, which in practice may help to improve the transport characteristics of Josephson junctions.