Cuozzo, Joseph - Sandia National Laboratories

Leggett modes and non-reciprocity in a Dirac semimetal

Topological materials are a broad class of materials which characteristically host surface states with electronic properties which are distinct from those in the bulk. When a topological material is incorporated into a heterostructure with a superconductor, exotic topological superconducting states can develop at the interface. These states are of fundamental interest since they can exhibit exotic electronic properties such as non-Abelian anyonic exchange, which is also crucial for topological quantum computing. In this poster, we will explore surface-bulk state interplay in topological superconducting heterostructures and discuss how novel phenomena can emerge in these heterostructures. We will first present results on our recent discovery of Leggett collective modes in Dirac semimetals (DSM). We will present a theoretical model for Leggett modes arising in DSM-based Josephson junctions and experimental verification of the mode in cadmium arsenide. Furthermore, our theoretical model predicts the observed signatures of the Leggett modes in cadmium arsenide are associated with a spontaneously broken time-reversal symmetry superconducting state. We present experiment evidence for this exotic state in the form of a zero-field supercurrent diode effect in cadmium arsenide across multiple devices and two different synthesis methods.