High-temperature topological superconductivity in twisted double layer copper oxides

TL;DR

This paper predicts that twisted bilayers of high-temperature copper oxide superconductors can host a robust, topologically nontrivial phase with chiral Majorana edge modes near 45° twist angles, potentially realizing high-temperature topological superconductivity.

Contribution

It introduces a new approach to realize high-temperature topological superconductivity using twisted bilayers of copper oxides, supported by symmetry and microscopic modeling.

Findings

Topological phase appears near 45° twist angle.

The phase is fully gapped and breaks time-reversal symmetry.

Topological superconductivity occurs close to 90 K, near the bulk T_c.

Abstract

A great variety of novel phenomena occur when two-dimensional materials, such as graphene or transition metal dichalcogenides, are assembled into bilayers with a twist between individual layers. As a new application of this paradigm, we consider structures composed of two monolayer-thin $d$-wave superconductors with a twist angle $\theta$ that can be realized by mechanically exfoliating van der Waals-bonded high-$T_c$ copper oxide materials, such as Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. On the basis of symmetry arguments and detailed microscopic modelling, we predict that for a range of twist angles in the vicinity of $45^{\rm o}$, such bilayers form a robust, fully gapped topological phase with spontaneously broken time-reversal symmetry and protected chiral Majorana edge modes. When $\theta\approx 45^{\rm o}$, the topological phase sets in at temperatures close to the bulk $T_c\simeq 90$ K, thus furnishing a long sought realization of a true high-temperature topological superconductor.