Tuning topological superconductivity within the t−J−U model of twisted bilayer cuprates

Maciej Fidrysiak; Bartłomiej Rzeszotarski; Józef Spałek

doi:10.1103/PhysRevB.108.224509

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Tuning topological superconductivity within the t−J−U model of twisted bilayer cuprates

Maciej Fidrysiak, Bartłomiej Rzeszotarski, Józef Spałek

DOI 10.1103/PhysRevB.108.224509 · Physical Review B

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Abstract

We carry out a theoretical study of unconventional superconductivity in twisted bilayer cuprates (TBCs) as a function of electron density and layer twist angle. The bilayer t−J−U model is employed and analyzed within the framework of a generalized variational wave function approach in the statistically consistent Gutzwiller formulation. The constructed phase diagram encompasses both a gapless d-wave state (reflecting the pairing symmetry of untwisted copper-oxides) and gapped d+eiφd phase that breaks spontaneously time reversal symmetry (TRS) and is characterized by a nontrivial Chern number. We find that the d+eiφd state occupies a nonconvex butterfly-shaped region in the doping versus twist-angle plane and demonstrate the presence of a reentrant TRS-breaking phase on the underdoped side of the phase diagram. This circumstance supports the emergence of topological superconductivity for fine-tuned twist angles in TBC away from 45∘. Our analysis of the microscopically derived Landau free-energy functional points toward sensitivity of the superconducting order parameter to small perturbations close to the topological state boundary.