Extremely strong coupling superconductivity in artificial two-dimensional Kondo lattices

TL;DR

This paper reports the discovery of extremely strong coupling superconductivity in artificially fabricated two-dimensional Kondo lattices, revealing enhanced critical fields and pairing strength due to reduced dimensionality.

Contribution

It demonstrates superconductivity in 2D heavy-fermion Kondo lattices, a significant step in understanding low-dimensional strongly correlated electron systems.

Findings

Superconductivity observed in 2D Ce-based Kondo lattices.

Enhanced upper critical field relative to transition temperature.

Strong coupling nature of electron pairs due to two-dimensional confinement.

Abstract

When interacting electrons are confined to low-dimensions, the electron-electron correlation effect is enhanced dramatically, which often drives the system into exhibiting behaviors that are otherwise highly improbable. Superconductivity with the strongest electron correlations is achieved in heavy-fermion compounds, which contain a dense lattice of localized magnetic moments interacting with a sea of conduction electrons to form a 3D Kondo lattice. It had remained an unanswered question whether superconductivity would persist upon effectively reducing the dimensionality of these materials from three to two. Here we report on the observation of superconductivity in such an ultimately strongly-correlated system of heavy electrons confined within a 2D square-lattice of Ce-atoms (2D Kondo lattice), which was realized by fabricating epitaxial superlattices built of alternating layers of heavy-fermion CeCoIn5 and conventional metal YbCoIn5. The field-temperature phase diagram of the superlattices exhibits highly unusual behaviors, including a striking enhancement of the upper critical field relative to the transition temperature. This implies that the force holding together the superconducting electron-pairs takes on an extremely strong coupled nature as a result of two-dimensionalization.