Unconventional Superconductivity in MgCNi3

TL;DR

This paper proposes that MgCNi3, a multiband superconductor, can exhibit an unconventional superconducting state with nontrivial phase relations, explaining experimental observations of both s-wave and unconventional features.

Contribution

It introduces a theoretical model for unconventional superconductivity in MgCNi3, highlighting the emergence of nontrivial phase relations and associated surface phenomena.

Findings

Presence of Andreev bound states at surfaces and impurities

Spontaneous currents indicative of unconventional pairing

Possible phase transitions between different order parameter symmetries

Abstract

A multiband superconductor with a conventional phonon mechanism can develop an unconventional state with a nontrivial order parameter phase relation between the individual bands. We propose that such a state can explain recent experimental results on MgCNi3, which are suggestive of both s-wave pairing symmetry and of unconventional superconductivity. We show that such a state gives rise to Andreev bound states, and to spontaneous currents, at surfaces and around impurities. We also investigate possible phase transitions between states with different order parameter symmetry.