We discuss the minimum value of the zero-bias differential conductance Gmin in a junction consisting of a normal metal and a nodal superconductor preserving time-reversal symmetry. Using the quasiclassical Green function method, we show that Gmin is quantized at (4e2/h)NZES in the limit of strong impurity scatterings in the normal metal. The integer NZES represents the number of perfect transmission channels through the junction. An analysis of the chiral symmetry of the Hamiltonian indicates that NZES corresponds to the Atiyah-Singer index in mathematics.
Cite
@article{arxiv.1604.05846,
title = {Quantization of Conductance Minimum and Index Theorem},
author = {Satoshi Ikegaya and Shu-Ichiro Suzuki and Yukio Tanaka and Yasuhiro Asano},
journal= {arXiv preprint arXiv:1604.05846},
year = {2020}
}