Specular Andreev reflection and its detection

We propose a universal method to detect the specular Andreev reflection taking the simple two-dimensional Weyl nodal-line semimetal-superconductor double-junction structure as an example. The quasiclassical quantization conditions are established for the energy levels of bound states formed in the middle semimetal along a closed path. The establishment of the conditions is completely based on the intrinsic character of the specularly reflected hole which has the same sign relation of its wave vector and group velocity as the incident electron. This brings about the periodic oscillation of conductance with the length of the middle semimetal, which is lacking for the retro-Andreev reflected hole with the opposite sign relation as the incident electron. The positions of the conductance peaks and the oscillation period can be precisely predicted by the quantization conditions. Our detection method is irrespective of the details of the materials, which may promote the experimental detection of and further research on the specular Andreev reflection as well as its applications in superconducting electronics.