Abstract
A Josephson junction (JJ) couples the supercurrent flowing between two weakly linked superconductors to the phase difference between them via a current-phase relation (CPR). While a sinusoidal CPR is expected for conventional junctions with insulating weak links, devices made from some exotic materials may give rise to unconventional CPRs and unusual Josephson effects. In this work, we present such a case: we investigate the proximity-induced superconductivity in SnTe nanowires by incorporating them as weak links in JJs and observe a deviation from the standard CPR. We report on indications of an unexpected breaking of time-reversal symmetry in these devices, detailing the unconventional characteristics that reveal this behavior. These include an asymmetric critical current in the DC Josephson effect, a prominent second harmonic in the AC Josephson effect, and a magnetic diffraction pattern with a minimum in critical current at zero magnetic field. The analysis examines how multiband effects and the experimentally visualized ferroelectric domain walls give rise to this behavior, giving insight into the Josephson effect in materials that possess ferroelectricity and/or multiband superconductivity.
Highlights
A Josephson junction (JJ) is a device where two superconductors are coupled by an insulating barrier, superconducting constriction, or conducting a weak link
Built into this current-phase relation (CPR) is a statement of time-reversal symmetry, which is reflected in the antisymmetric property IS(φ) = − IS(−φ) of the CPR1
JJs have been created with superconductors or weak links which possess broken time-reversal symmetry (BTRS)
Summary
A Josephson junction (JJ) is a device where two superconductors are coupled by an insulating barrier, superconducting constriction, or conducting a weak link. The second is a CPR which is dominated by a second harmonic, a result of either the presence of transport channels that are out of phase—so-called "0" and "π" supercurrent channels—or a Josephson coupling that vanishes in the first order This asymmetric critical current and dominant second harmonic have been predicted and/or measured in JJs with materials containing ferromagnetism[2,3,12,13,14,15] or spin-orbit interaction in the presence of a magnetic field[16,17], d-wave superconductors[9], multiband superconductors[18,19,20,21,22,23], and topological (p-wave) superconductors[24,25,26,27]
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