Alexey Taskin

Inducing superconducting (SC) correlations in the one-dimensional edge state of Quantum Anomalous Hall Insulator (QAHI) by SC proximity effect might bring an exotic topological superconductivity hosting non-Abelian anyons.

Here we report the observation of crossed Andreev reflection (CAR) across a narrow superconducting Nb electrode contacting the chiral edge state of a QAHI device, evinced by a negative nonlocal voltage measured downstream from the grounded Nb electrode. In the CAR process, an electron in the chiral edge entering a grounded SC electrode creates a Cooper pair by taking another electron from the other side of the electrode, leaving a hole in the downstream edge, which is responsible for the measured negative downstream nonlocal voltage. Importantly, the observation of the CAR process is a direct evidence of SC correlations induced in the chiral edge state. Our theoretical analysis demonstrates that this CAR process does not strongly dependent on the nature of the superconductivity that mediates it. Nevertheless, the characteristic length of the CAR process is found to be much longer than the superconducting correlation length in Nb, which suggests that the CAR is mediated by superconductivity induced on the QAHI surface.