Topological superconductivity in a van der Waals heterostructure*

Van der Waals (vdW) heterostructures have emerged as a playground for realizing and engineering exotic quantum states not found in naturally occurring materials. Use of vdW heterostructures allows combining materials with very different properties. In these designer heterostructures, the desired physics emerges through the engineered interactions between the different components.The use of vdW heterostructures further facilitates using these effects in future device structures and potentially allow further control through e.g. electrostatic gating. 

I will outline our recent results on realizing topological superconductivity in a vdW heterostructure. We use molecular-beam epitaxy (MBE) in ultra-high vacuum to grow CrBr₃ on superconducting NbSe₂ substrates and characterize the resulting samples using low-temperature scanning tunneling microscopy (STM). These samples combine out of plane  ferromagnetism, Rashba-type spin-orbit interactions and s-wave superconductivity, which are the necessary ingredients for topological superconductivity. I will discuss how the moiré pattern due to the lattice mismatch between CrBr₃ and NbSe₂ is essential ingredient in this system as it profoundly modifies the topological phase diagram and enables the realization of a topological superconducting state that would not be accessible in the absence of the moiré. These results highlight the versatility of vdW heterostructures in realizing quantum states that are difficult to find and control in naturally occurring materials.