Intertwined Magnetism and Superconductivity in Isolated Correlated Flat Bands

Abstract

Multi-orbital electronic models hosting a non-trivial 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) pseudo-spin non-linear 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 non-trivial band-topology.

13 pages, 12 figures; published version

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• Superconductivity and pair density waves from nearest-neighbor interactions in frustrated lattice geometries
• Identifying Instabilities with Quantum Geometry in Flat Band Systems
• Enhanced Andreev Reflection in Flat-Band Systems: Wave Packet Dynamics, DC Transport and the Josephson Effect
• Gaplessness from disorder and quantum geometry in gapped superconductors