The Andreev reflection in a superconductor-normal metal junction of a doped correlated quantum spin Hall insulator.
Yung-Yeh Chang1*, Chung-Yu Mou2, Chung-Hou Chung1,3
1Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
2Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
3Physics Division, National Center for Theoretical Sciences, Hsinchu, Taiwan
* presenting author:Yung-Yeh Chang,
Andreev conductance across a normal metal-superconductor (N-S) junction of doped correlated quantum spin Hall insulator on honeycomb lattice is theoretically studied via Blonder-Tinkham-Klapwijk (BTK) formalism. The normal side is modeled by the doped Kane-Mele (KM) model. The superconducting side is a doped correlated KM t-J model, which has been shown to feature d+id'-wave spin singlet pairing. With increasing intrinsic spin-orbit coupling, the doped KM t-J system undergoes a topological phase transition from the chiral d-wave superconductivity to the Z₂ spin-Chern superconducting phase with helical Majorana fermions at edges. We apply a local strain on the N-S interface to generate an effective Dirac-delta barrier and study the transport near the chiral-helical phase transition in the weak tunneling limit. We explore the Andreev conductance at the K and K’ Dirac points, respectively and find the distinctive behaviors across the transition. Relevance of our results for the adatom-doped graphene is discussed. Reference: S.J. Sun, C.H. Chung, Y.Y. Chang, W.F. Tsai, and F.C. Zhang, arxiv:1506.02584.

Keywords: Andreev reflection, D-wave superconductor