Eavesdropping on competing condensates by the edge supercurrent in a Weyl superconductor.

Abstract

In a topological insulator the metallic surface states are easily distinguished from the insulating bulk states [1]. By contrast, in a topological superconductor [2-5], much less is known about the relationship between an edge supercurrent and the bulk pair condensate. Can we force their pairing symmetries to be incompatible? In the superconducting state of the Weyl semimetal MoTe$_2$, an edge supercurrent is observed as oscillations in the current-voltage (\emph{I-V}) curves induced by fluxoid quantization [6]. We have found that the $s$-wave pair field of supercurrent injected from niobium contacts is incompatible with the intrinsic pair condensate in MoTe$_2$. The incompatibility leads to strong stochasticity in the switching current $I_c$ as well as other anomalous properties such as an unusual antihysteretic behavior with the ``wrong'' sign. Under the injected supercurrent, the fluxoid-induced edge oscillations survive to much higher magnetic fields \emph{H}. Interestingly, the oscillations are either very noisy or noise-free depending on the pair field that ends up dictating the edge pairing. Using the phase noise as a sensitive probe that eavesdrops on the competiting bulk states, we uncover an underlying blockade mechanism whereby the intrinsic condensate can pre-emptively block proximitization by the Nb pair field depending on the history.