Emergent exotic superconductivity in artificially-engineered tricolor Kondo superlattices

TL;DR

This study demonstrates that artificially-engineered tricolor Kondo superlattices exhibit tunable Rashba spin-orbit interaction, leading to novel superconducting states with unusual critical field behaviors and potential helical or stripe phases.

Contribution

It introduces a new method to induce and control Rashba effect in 2D strongly correlated electron systems via tricolor superlattices, revealing altered superconducting properties.

Findings

Rashba SOI causes significant changes in superconductivity of CeCoIn$_5$

Superconducting properties are tunable by layer thickness

Anomalous low-temperature upturn in critical field suggests exotic phases

Abstract

In the quest for exotic superconducting pairing states, the Rashba effect, which lifts the electron-spin degeneracy as a consequence of strong spin-orbit interaction (SOI) under broken inversion symmetry, has attracted considerable interest. Here, to introduce the Rashba effect into two-dimensional (2D) strongly correlated electron systems, we fabricate non-centrosymmetric (tricolor) superlattices composed of three kinds of $f$-electron compounds with atomic thickness; $d$-wave heavy fermion superconductor CeCoIn$_5$ sandwiched by two different nonmagnetic metals, YbCoIn$_5$ and YbRhIn$_5$. We find that the Rashba SOI induced global inversion symmetry breaking in these tricolor Kondo superlattices leads to profound changes in the superconducting properties of CeCoIn$_5$, which are revealed by unusual temperature and angular dependences of upper critical fields that are in marked contrast with the bulk CeCoIn$_5$ single crystals. We demonstrate that the Rashba effect incorporated into 2D CeCoIn$_5$ block layers is largely tunable by changing the layer thickness. Moreover, the temperature dependence of in-plane upper critical field exhibits an anomalous upturn at low temperatures, which is attributed to a possible emergence of a helical or stripe superconducting phase. Our results demonstrate that the tricolor Kondo superlattices provide a new playground for exploring exotic superconducting states in the strongly correlated 2D electron systems with the Rashba effect.