Resonant nonlocal Andreev reflection in a narrow quantum spin Hall system

We theoretically investigate the Andreev reflection process in a quantum spin Hall insulator strip touching on an s-wave superconductor, taking into account the interedge coupling. Under the resonant condition, all incident electrons are converted into holes on the other side of the junction through nonlocal Andreev reflection. There is no processes of local Andreev reflection, elastic cotunneling, or normal reflection and therefore entangled electron pairs can be generated separately with a high efficiency. The tunneling conductance and the noise power are also presented.