Evidence of topological superconductivity in planar Josephson junctions

Author(s): Antonio Fornieri [sup.1] , Alexander M. Whiticar [sup.1] , F. Setiawan [sup.2] , Elías Portolés [sup.1] , Asbjørn C. C. Drachmann [sup.1] , Anna Keselman [sup.3] , Sergei Gronin [...]
Majorana zero modes--quasiparticle states localized at the boundaries of topological superconductors--are expected to be ideal building blocks for fault-tolerant quantum computing.sup.1,2. Several observations of zero-bias conductance peaks measured by tunnelling spectroscopy above a critical magnetic field have been reported as experimental indications of Majorana zero modes in superconductor-semiconductor nanowires.sup.3-8. On the other hand, two-dimensional systems offer the alternative approach of confining Majorana channels within planar Josephson junctions, in which the phase difference [phi] between the superconducting leads represents an additional tuning knob that is predicted to drive the system into the topological phase at lower magnetic fields than for a system without phase bias.sup.9,10. Here we report the observation of phase-dependent zero-bias conductance peaks measured by tunnelling spectroscopy at the end of Josephson junctions realized on a heterostructure consisting of aluminium on indium arsenide. Biasing the junction to [phi] [almost equal to] [pi] reduces the critical field at which the zero-bias peak appears, with respect to [phi] = 0. The phase and magnetic-field dependence of the zero-energy states is consistent with a model of Majorana zero modes in finite-size Josephson junctions. As well as providing experimental evidence of phase-tuned topological superconductivity, our devices are compatible with superconducting quantum electrodynamics architectures.sup.11 and are scalable to the complex geometries needed for topological quantum computing.sup.9,12,13. Evidence is found for phase-tunable Majorana zero modes in scalable two-dimensional Josephson junctions produced by top-down fabrication.