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A phenomenological theory of zero-energy Andreev resonant states
A conceptual consideration is given to a zero-energy state (ZES) at the
surface of unconventional superconductors. The reflection coefficients in
normal-metal / superconductor (NS) junctions are calculated based on a
phenomenological description of the reflection processes of a quasiparticle.
The phenomenological theory reveals the importance of the sign change in the
pair potential for the formation of the ZES. The ZES is observed as the
zero-bias conductance peak (ZBCP) in the differential conductance of NS
junctions. The split of the ZBCP due to broken time-reversal symmetry states is
naturally understood in the present theory. We also discuss effects of external
magnetic fields on the ZBCP.Comment: 12 page