Twisted multilayer nodal superconductors

TL;DR

This paper explores twisted multilayer nodal superconductors, revealing new phenomena such as magic angles and chiral topological phases, expanding understanding beyond bilayer systems.

Contribution

It extends the analysis of twisted bilayer superconductors to multilayers, identifying novel features like magic angles and topological phases.

Findings

Alternating twist multilayers map to bilayers with renormalized couplings.

Constant twist multilayers exhibit cubic band crossings at magic angles.

Both stackings support chiral topological superconductivity.

Abstract

Twisted bilayers of nodal superconductors were recently proposed as a promising platform to host superconducting phases that spontaneously break time-reversal symmetry. Here we extend this analysis to twisted multilayers, focusing on two high-symmetry stackings with alternating ($\pm \theta$) and constant ($\theta$) twist angles. In analogy to alternating-twist multilayer graphene, the former can be mapped to twisted bilayers with renormalized interlayer couplings, along with a remnant gapless monolayer when the number of layers $L$ is odd. In contrast, the latter exhibits physics beyond twisted bilayers, including the occurrence of `magic angles' characterized by cubic band crossings when $L \mod 4 = 3$. Owing to their power-law divergent density of states, such multilayers are highly susceptible to secondary instabilities. Within a BCS mean-field theory, defined in the continuum and on a lattice, we find that both stackings host chiral topological superconductivity in extended regions of their phase diagrams.