Intertwined Superconductivity and Magnetism from Repulsive Interactions in Kondo Bilayers

TL;DR

This paper demonstrates a novel strong-coupling mechanism where purely repulsive interactions induce intertwined superconductivity and magnetism in a Kondo bilayer system, supported by numerical simulations and theoretical analysis.

Contribution

It introduces a new mechanism for superconductivity arising from repulsive interactions in coupled electron systems, with a comprehensive phase diagram and robust pairing beyond strong coupling.

Findings

Superconductivity coexists with magnetism over a wide range of interlayer couplings.

Rich phase diagram with antiferromagnetic and ferromagnetic orders in different dimensions.

Robust pairing mechanism applicable to nickelates and moire heterostructures.

Abstract

While superconductors are conventionally established by attractive interactions, higher-temperature mechanisms for emergent electronic pairing from strong repulsive electron-electron interactions remain under considerable scrutiny. Here, we establish a strong-coupling mechanism for intertwined superconductivity and magnetic order from purely repulsive interactions in a Kondo-like bilayer system, composed of a two-dimensional Mott insulator coupled to a layer of weakly-interacting itinerant electrons. Combining large scale DMRG and Monte Carlo simulations, we find that superconductivity persists and coexists with magnetism over a wide range of interlayer couplings. We classify the resulting rich phase diagram and find 2-rung antiferromagnetic and 4-rung antiferromagnetic order in one-dimensional systems along with a phase separation regime, while finding that superconductivity coexists with either antiferromagnetic or ferromagnetic order in two dimensions. Remarkably, the model permits a rigorous strong-coupling analysis via localized spins coupled to charge-2e bosons through Kugel-Khomskii interactions, capturing the pairing mechanism in the presence of magnetism due to emergent attractive interactions. Our numerical analysis reveals that pairing remains robust well beyond the strong-coupling regime, establishing a new mechanism for superconductivity in coupled weakly- and strongly-interacting electron systems, relevant for infinite-layer nickelates and superconductivity in moire multilayer heterostructures.