Magic angles and correlations in twisted nodal superconductors

Abstract

Motivated by the recent achievements in the realization of strongly correlated and topological phases in twisted van der Waals heterostructures, we study the low-energy properties of a twisted bilayer of nodal superconductors. It is demonstrated that the spectrum of the superconducting Dirac quasiparticles close to the gap nodes is strongly renormalized by twisting and can be controlled with magnetic fields, current, or interlayer voltage. In particular, the application of an interlayer current transforms the system into a topological superconductor, opening a topological gap and resulting in a quantized thermal Hall effect with gapless, neutral edge modes. Close to the "magic angle," where the Dirac velocity of the quasiparticles is found to vanish, a correlated superconducting state breaking time-reversal symmetry is shown to emerge. Estimates for a number of superconducting materials, such as cuprate, heavy fermion, and organic nodal superconductors, show that twisted bilayers of nodal superconductors can be readily realized with current experimental techniques.

Supercurrent-induced topological phase transitions

“…Therefore our results contain the thermodynamically unstabilizable states without an external current source. Second, Volkov et al studied a supercurrent-induced topological phase transition in a twisted bilayer nodal superconductors very recently [40]. Although we admit their basic idea and the mechanism are similar to ours, there are several important differences as follows: (i) Our focus is on generic phenomena which can occur in various families of superconductors, while they are focusing on the specific interesting example and the relation to the twistronics.…”

“…V, we have considered a perturbation (16), which breaks the mirror symmetry in the x-direction. One possible way to break the mirror symmetry is to use twisted double-layered cuprate thin films [40,76]. Also, using a substrate lacking mirror symmetry might be another way.…”

“…[35][36][37], after the strong pump by a laser field, the induced supercurrent effectively breaks the inversion symmetry and the second harmonic response is observed in the current-carrying state. This motivates us to study the control of superconductors via electric current [38][39][40][41][42]. From the theoretical point of view, we can study the leading effect of supercurrent within equilibrium states, and it makes the problem more tractable than the normal * takasan@berkeley.edu…”

Supercurrent-Induced Weyl Superconductivity

“…This can be detected in principle using the ARPES, which probes the quasiparticle spectrum of the filled states, and it can be a clear signature of the Weyl superconductivity. Although we admit that the current-induced gap is not so large and the experimental detection is challenging, many theoretical studies have suggested topological superconductivity with a finite COM momentum [56][57][58][59][60][61][62][63][64][65][66][67][68]. Therefore, we expect that further promising experimental setups are proposed and such a topological phase is observed in future works.…”

“…Furthermore, in our previous work, we have elucidated the possibility of supercurrent-induced topological phase transition in two-dimensional (2D) noncentrosymmetric superconductors [56]. Such a topological superconducting phase with a finite center-of-mass (COM) momentum of the Cooper pairs has garnered significant attention recently [57][58][59][60][61][62][63][64][65][66][67][68].…”