Tuning the pairing interaction in a $d$-wave superconductor by paramagnons injected through interfaces

TL;DR

This study demonstrates that magnetic fluctuations (paramagnons) injected through interfaces in heterostructures can significantly enhance and tune the pairing interaction in a $d$-wave superconductor, especially near magnetic quantum critical points.

Contribution

It introduces a novel interface engineering approach to control superconducting pairing interactions via magnetic fluctuations in heterostructures.

Findings

Superconductivity coexists with antiferromagnetism in layered heterostructures.

The pairing interaction becomes extremely strong near the critical pressure where AFM order vanishes.

Interface-mediated magnetic fluctuations can maximize the superconducting pairing strength.

Abstract

Unconventional superconductivity and magnetism are intertwined on a microscopic level in a wide class of materials. A new approach to this most fundamental and hotly debated issue focuses on the role of interactions between superconducting electrons and bosonic fluctuations at the interface between adjacent layers in heterostructures. Here we fabricate hybrid superlattices consisting of alternating atomic layers of heavy-fermion superconductor CeCoIn$_5$ and antiferromagnetic (AFM) metal CeRhIn$_5$, in which the AFM order can be suppressed by applying pressure. We find that the superconducting and AFM states coexist in spatially separated layers, but their mutual coupling via the interface significantly modifies the superconducting properties. An analysis of upper critical fields reveals that near the critical pressure where AFM order vanishes, the force binding superconducting electron-pairs acquires an extremely strong-coupling nature. This demonstrates that superconducting pairing can be tuned non-trivially by magnetic fluctuations (paramagnons) injected through the interface, leading to maximization of the pairing interaction.