Exploring topological superconductivity in topological insulator – superconductor hybrid devices

Topological insulators (TIs) coupled to s-wave superconductors (SC) are predicted to harbor a topological superconducting phase. In this talk, I will first talk about the SC-TI-SC junctions, where an anomalous enhancement of the critical current at low temperatures and a highly non-sinusoidal current-phase relation were observed. These results suggest superconductivity is induced in the spin-helical topological surface states and point toward nearly ballistic nature of superconducting transport. I will then introduce our recent work about the induced SC in a quantum anomalous Hall (QAH) insulator, as a potential platform for the realization of “chiral Majorana modes”. A recent transport experiment claimed the half-quantized two-terminal conductance plateau in a millimeter-size QAH – Nb hybrid structure as evidence for the chiral Majorana modes. However, there are serious concerns about this interpretation because non-Majorana mechanisms can also generate similar signatures, especially in a disordered QAH system. I will present a systematic study of the superconducting contact transparency and its influence on the two-terminal conductance measurements and provide a non-Majorana explanation for the appearance of the half-quantized plateau in the QAH – Nb hybrid devices.