Altermagnetism and superconductivity in a multiorbital t−J model

Abstract

Motivated by exploring correlated multiorbital altermagnets (AℓMs) we study minimal t−J models on the square-octagon lattice, which favors such a collinear magnetic order. While antiferromagnetic order breaks translational and time-reversal symmetries, the AℓM state (equivalently, a “d-wave ferromagnet”) features multipolar order, which separately breaks time-reversal and crystal rotation symmetries but preserves their product leading to spin-split bands with zero net magnetization. We study the mean-field phase diagram of these multiorbital models as we vary doping and interactions, discovering two types of AℓM order: (i) itinerant weak-coupling AℓM metals driven by quasi-1D van Hove singularities, as well as (ii) strong AℓM order at half-filling. We also find regimes of superconductivity including uniform s-wave and dxy-wave pairing states, incipient dxy-wave pair density wave order, and uniform phases with coexisting singlet-triplet pairing and AℓM order. Our inhomogeneous mean-field theory approach reveals that the coexistence phases are unstable to phase separation, but longer-range interactions could lead to stripe order. Our results may be relevant to studies of doping and pressure on AℓM materials.

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