Abstract
We investigate supercurrent interference patterns measured as a function of magnetic field in ballistic graphene Josephson junctions. At high doping, the expected $\Phi_{0}$-periodic "Fraunhofer" pattern is observed, indicating a uniform current distribution. Close to the Dirac point, we find anomalous interference patterns with an apparent 2$\Phi_{0}$ periodicity, similar to that predicted for topological Andreev bound states carrying a charge of $e$ instead of $2e$. This feature persists with increasing temperature, ruling out a non-sinusoidal current-phase relationship. It also persists in junctions in which sharp vacuum edges are eliminated. Our results indicate that the observed behavior may originate from an intrinsic property of ballistic graphene Josephson junctions, though the exact mechanism remains unclear.
Highlights
The critical current of a Josephson junction subject to a perpendicular magnetic field is known to show decaying oscillations [1,2]
We start by measuring the samples at high density, where we find conventional 0-periodic Fraunhofer patterns
The patterns with even node lifting were repeatedly observed in several devices of different geometries, making it highly unlikely that the behavior is a result of an aberrant, nonuniform current density
Summary
The critical current of a Josephson junction subject to a perpendicular magnetic field is known to show decaying oscillations [1,2]. For a uniform supercurrent distribution and a 2π -periodic sinusoidal current-phase relation, the pattern of oscillations is identical to that of single-slit Fraunhofer interference in optics. We start by measuring the samples at high density, where we find conventional 0-periodic Fraunhofer patterns.
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