Anomalous Upper Critical Field in CeCoIn_5/YbCoIn_5 Superlattices with a Rashba-type Heavy Fermion Interface

TL;DR

This study investigates the unusual angular dependence of the upper critical field in CeCoIn_5/YbCoIn_5 superlattices, revealing potential exotic superconducting states influenced by Rashba-type effects and local inversion symmetry breaking.

Contribution

It demonstrates how the upper critical field behavior varies with layer thickness, indicating the emergence of exotic superconducting states due to Rashba-type effects at the interface.

Findings

H_{c2}( heta) exhibits a cusp near parallel field for n=3 superlattice.

The cusp disappears for n=4 and 5, indicating a change in dominant depairing effects.

Results suggest possible realization of helical superconducting states at high magnetic fields.

Abstract

We report a highly unusual angular variation of the upper critical field (H_c2) in epitaxial superlattices CeCoIn_5(n)/YbCoIn_5(5), formed by alternating layers of n and a 5 unit-cell thick heavy-fermion superconductor CeCoIn_5 with a strong Pauli effect and normal metal YbCoIn_5, respectively. For the n=3 superlattice, H_{c2}(\theta) changes smoothly as a function of the field angle \theta. However, close to the superconducting transition temperature, H_{c2}(\theta) exhibits a cusp near the parallel field (\theta=0 deg). This cusp behavior disappears for n=4 and 5 superlattices. This sudden disappearance suggests the relative dominance of the orbital depairing effect in the n=3 superlattice, which may be due to the suppression of the Pauli effect in a system with local inversion symmetry breaking. Taking into account the temperature dependence of H_{c2}(\theta) as well, our results suggest that some exotic superconducting states, including a helical superconducting state, might be realized at high magnetic fields.