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.

References

The exact role played by the training is not understood.

— Indirect Tunneling Enabled Spontaneous Time-Reversal Symmetry Breaking and Josephson Diode Effect in TiN/Al$_2$O$_3$/Hf$_{0.8}$Zr$_{0.2}$O$_2$/Nb tunnel junctions  (2504.16987 - Ding et al., 23 Apr 2025) in Section: Spontaneous TRS breaking and electrical control of the JD effect

However, reversible control of the magnetic order together with the diode polarity remained elusive in that system, leaving their microscopic connection open and limiting direct application in quantum circuits.

— Reversible field-free superconducting diode effect controlled by an antiferromagnet  (2609.38003 - Krizek et al., 29 Sep 2026) in Introduction