High-temperature topological superconductivity in twisted double-layer copper oxides

As a new application of the twist paradigm, we predict that structures composed of two-monolayer-thin d-wave superconductors with a twist angle close to 45° form a robust, fully gapped topological phase with spontaneously broken time-reversal symmetry and protected chiral Majorana edge modes. These structures can be realized by mechanically exfoliating van der Waals-bonded high-T_c copper oxide materials, such as Bi₂Sr₂CaCu₂O_{8 + δ}. Our symmetry arguments and detailed microscopic modelling suggest that this phase will form for a range of twist angles in the vicinity of 45°, and will set in at a temperature close to the bulk superconducting critical temperature of 90 K. Therefore, this platform may provide a long-sought realization of a true high-temperature topological superconductor. Experimentally observable signatures of the T-broken topological phase, including the polar Kerr effect, anomalous Josephson effect and various spectroscopies will also be discussed.