InAs-Al hybrid devices passing the topological gap protocol

Abstract

We present measurements and simulations of semiconductor-superconductor heterostructure devices that are consistent with the observation of topological superconductivity and Majorana zero modes. The devices are fabricated from high-mobility two-dimensional electron gases in which quasi-one-dimensional wires are defined by electrostatic gates. These devices enable measurements of local and nonlocal transport properties and have been optimized via extensive simulations to ensure robustness against nonuniformity and disorder. Our main result is that several devices, fabricated according to the design's engineering specifications, have passed the topological gap protocol defined in Pikulin et al. (arXiv:2103.12217). This protocol is a stringent test composed of a sequence of three-terminal local and nonlocal transport measurements performed while varying the magnetic field, semiconductor electron density, and junction transparencies. Passing the protocol indicates a high probability of detection of a topological phase hosting Majorana zero modes as determined by large-scale disorder simulations. Our experimental results are consistent with a quantum phase transition into a topological superconducting phase that extends over several hundred millitesla in magnetic field and several millivolts in gate voltage, corresponding to approximately one hundred microelectronvolts in Zeeman energy and chemical potential in the semiconducting wire. These regions feature a closing and reopening of the bulk gap, with simultaneous zero-bias conductance peaks at both ends of the devices that withstand changes in the junction transparencies. The extracted maximum topological gaps in our devices are 20-60μeV. This demonstration is a prerequisite for experiments involving fusion and braiding of Majorana zero modes.