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Symmetry conditions of a nodal superconductor for generating robust flat-band Andreev bound states at its dirty surface
We discuss the symmetry property of a nodal superconductor that hosts robust
flat-band zero-energy states at its surface under potential disorder. Such
robust zero-energy states are known to induce the anomalous proximity effect in
a dirty normal metal attached to a superconductor. A recent study has shown
that a topological index describes the number of
zero-energy states at the dirty surface of a -wave superconductor. We
generalize the theory to clarify the conditions required for a superconductor
that enables . Our results show that is realized in a topological material that belongs to
either the BDI or CII class. We also present two realistic Hamiltonians that
result in .Comment: 9 pages, 3 figure
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