Topological superconductivity in twisted double-layer high-Tc cuprates: Theory, experimental signatures and applications

Structures composed of two monolayer-thin d-wave superconductors with a twist angle close to 45° are predicted to form a robust, fully gapped topological superconducting phase with spontaneously broken time-reversal symmetry and protected chiral edge modes. In this talk I will review the theory behind the topological phase and discuss recent experimental efforts to fabricate and probe twisted flakes of high-T_c cuprate Bi₂Sr₂CaCu₂O_8+δ. Signatures of d-wave symmetry and of spontaneous T-breaking are indeed visible in the device Josephson current response, as detected through a pronounced superconducting diode effect observed in samples near 45° twist but absent in untwisted samples. Time permitting, a potential application of this new physics to an improved transmon qubit will also be discussed.