Topological Superconductivity in Twisted Superconductors of Finite Thickness

Twisted bilayers of nodal superconductors have been predicted to host topological states under the application of interlayer supercurrent. Experimentally it is, however, more practical to twist superconducting flakes of finite thickness, containing several layers each. We consider a system of one monolayer d_x²-y² superconductor stacked with a twist on top of a N-layer flake. Under application of c-axis supercurrent through the system, we find that a topological gap opens in the bulk of the system with gapless edge modes. While the gap value decreases with N, the Chern number increases as |C| = 2(N+1). We discuss the dependence of the results on the interlayer tunneling strength, as well as signatures of the topological superconducting state in the thermal Hall conductance and local density of states, measurable in STM experiments.