Mechanism of training-current control of Josephson diode polarity

Determine the microscopic mechanism by which a large normal-state training current controls the polarity and magnitude of the nonreciprocal critical current (Josephson diode effect) in TiN/Al2O3/Hf0.8Zr0.2O2/Nb Josephson tunnel junctions fabricated by atomic layer deposition, including whether persistent bound interfacial charge at the Al2O3/Hf0.8Zr0.2O2 interface modifies the occupancy of localized barrier states and thereby tunes the balance between positive and negative local Josephson couplings.

Background

The experiments show that applying a large normal-state "training" current reversibly sets the polarity of the Josephson diode effect and significantly enhances diode efficiency. The effect is erased by warming above 10 K, suggesting an electrically controlled, nonmagnetic origin.

The authors attribute the diode behavior to coexistence of positive and negative local Josephson couplings, with the negative contributions arising from indirect tunneling via localized states in the barrier. They hypothesize that training currents may generate persistent bound charge at the Al2O3/Hf0.8Zr0.2O2 interface, which could alter localized-state occupancies and thus the balance of local couplings, but the exact mechanism is not yet established.