Intertwined magnetism and superconductivity in isolated correlated flat bands

Abstract

Multiorbital electronic models hosting a nontrivial band topology in the regime of strong electronic interactions are an ideal playground for exploring a host of complex phenomenology. We consider here a sign-problem-free and time-reversal symmetric model with isolated topological (Chern) bands involving both spin and valley degrees of freedom in the presence of a class of repulsive electronic interactions. Using a combination of numerically exact quantum Monte Carlo computations and analytical field-theoretic considerations, we analyze the phase diagram as a function of the flat-band filling, temperature, and relative interaction strength. The low-energy physics is described in terms of a set of intertwined orders—a spin-valley Hall (SVH) insulator and a spin-singlet superconductor (SC). Our low-temperature phase diagram can be understood in terms of an effective SO(4) pseudospin nonlinear sigma model. Our work paves the way for building more refined and minimal models of realistic materials, including moiré systems, to study the universal aspects of competing insulating phases and superconductivity in the presence of nontrivial band topology.

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