Unconventional superconducting transport in semiconductor Dirac materials

• Applicant: Dr. Grigory Tkachov, Ph.D.
• Subject Area: Theoretical Condensed Matter Physics
• Term: from 2013 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 231149113

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.

• DFG Programme: Research Grants
• Participating Person: Professorin Dr. Ewelina M. Hankiewicz