Unconventional superconductivity in CeCoIn5 with magnetic texture and orbital quantization

TL;DR

This paper presents experimental evidence of the FFLO phase in CeCoIn5, showing a spatially modulated superconducting state with multiple phase transitions, revealing complex vortex structures and the interplay of magnetism and superconductivity.

Contribution

It provides the first clear experimental observation of the FFLO phase in CeCoIn5, including detailed heat capacity and magnetization measurements showing multiple phase transitions.

Findings

Evidence of a second phase transition within superconductivity.

Observation of cascade of first order phase transitions.

Identification of Landau level vortex states with multiquanta vortices.

Abstract

A sufficiently high magnetic field applied to a superconductor will act on both the charge and the spin of the individual electrons breaking up the Cooper pairs. If the spin effect dominates, the superconducting state can develop a texture before eventually entering the normal state with increasing magnetic field. This spatially varying superconducting state is a periodic array of magnetic walls separated by superconducting regions. Known as the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, it was predicted in 1964. We report heat capacity measurements on the heavy fermion superconductor, CeCoIn5, which reveal a second phase transition within the superconducting state, clear evidence of the FFLO phase. We also report magnetization measurements that display a cascade of first order phase transitions within the FFLO region. Each transition indicates an increase in orbital momentum of the superconducting order parameter and corresponds to a specific Landau level vortex state comprised of multiquanta vortices. The experimental realization of the FFLO state provides a new opportunity to study the symbiosis of magnetism and superconductivity, two states of matter once thought to be mutually exclusive.