Spin-Polaron Mediated Superconductivity in Doped Chern Antiferromagnets

TL;DR

This paper investigates how doping Chern antiferromagnets leads to spin-polaron mediated superconductivity, revealing a rich phase diagram with magnetic order and unconventional superconductivity in a tunable topological model.

Contribution

It introduces a sign-problem-free model with tunable Chern bands and demonstrates superconductivity emerging from a ferromagnetic and antiferromagnetic ordered state upon doping.

Findings

Ground state hosts intra-valley ferromagnetic coherence and inter-valley antiferromagnetism.

Superconductivity develops upon doping, with electrons dressed by spin-flip excitations.

Spin-polaron excitations persist with weak spin-orbit coupling.

Abstract

The study of interacting topological bands with a tunable bandwidth offers a unique platform to study the interplay of intertwined orders and emergent non-electronic excitations. Here we design a time-reversal symmetric and sign-problem-free electronic model with tunable Chern bands carrying valley-contrasting Chern number, interacting via competing (anti-)ferromagnetic interactions. Using numerically exact quantum Monte-Carlo computations, we analyze the many-body phase-diagram as a function of temperature and band filling fractions over a wide range of electronic bandwidth, interaction anisotropy, and an Ising spin-orbit coupling. At a commensurate filling of the Chern bands, the ground state hosts intra-valley ferromagnetic coherence and inter-valley antiferomagnetism, thus realizing an insulating Chern antiferromagnet (CAF). Upon doping, the ground-state develops superconductivity, but where the low-energy charged quasiparticles are composite objects -- electrons dressed by multiple spin-flip excitations. These spin-polaron (or skyrmion) excitations persist in the presence of a weak spin-orbit coupling. In a companion article, we address the emergent symmetries and low-energy field-theoretic aspects of the problem and reveal the proximity to a deconfined quantum critical point. We end by providing a general outlook towards building microscopic connections with models of interacting moir\'e materials, including twisted bilayer graphene, where many of the ingredients considered here are naturally present.