Theory of the proximity effect in junctions with unconventional superconductors

TL;DR

This paper develops a comprehensive theoretical framework for understanding the proximity effect in junctions between diffusive normal metals and various classes of unconventional superconductors, considering different symmetry states.

Contribution

It introduces a general quasiclassical Green's function approach to analyze the symmetry and spectral properties of induced pair amplitudes for multiple unconventional superconductor states.

Findings

Pair amplitude in DN matches superconductor symmetry: ESE, OTE, OTE, ESE.

Symmetry properties of induced pair amplitudes are systematically determined.

Theoretical predictions for the spectral features of proximity-induced states.

Abstract

We present a general theory of the proximity effect in junctions between diffusive normal metals (DN) and unconventional superconductors in the framework of the quasiclassical Green's function formalism. Various possible symmetry classes in a superconductor are considered which are consistent with the Pauli principle: even-frequency spin-singlet even-parity (ESE) state, even-frequency spin-triplet odd-parity (ETO) state, odd-frequency spin-triplet even-parity (OTE) state and odd-frequency spin-singlet odd-parity (OSO) state. For each of the above four cases symmetry and spectral properties of the induced pair amplitude in the DN are determined. It is shown that the pair amplitude in a DN belongs respectively to an ESE, OTE, OTE and ESE pairing state.