Magnetically Induced Switching-Current Jumps in InAs/Al Josephson Junctions

Abstract: We report Barkhausen-like switching at millitesla fields in an $n$-doped InAs/Al nanowire Josephson junction, which serves as an interferometric probe of intrinsic magnetic reconfigurations, as evidenced by discrete switching-current jumps. At $T=30$~mK the device displays a Fraunhofer-like modulation with $I_{\mathrm{sw}}(0)\approx 0.24~μ\mathrm{A}$ and an abrupt transition at $|B|\approx 3~\mathrm{mT}$ between two branches differing by $ΔI_{\mathrm{sw}}\approx 0.13~μ\mathrm{A}$. By tracking the characteristic field scales from $30$ to $900$~mK, we find that the jump field is essentially temperature-independent, whereas the superconducting critical field decreases with temperature, as expected for thin Al films. The sharp discontinuity, sweep-direction asymmetry, and reproducibility across repeated scans point to avalanche-like switching between metastable magnetic configurations of the local magnetic texture, which are directly coupled to the weak link. Within an effective-field framework, each reconfiguration modifies a local field offset, thereby reshaping the interference response and leading to an abrupt reorganization of the switching-current pattern.

• The paper presents experimental evidence of abrupt, Barkhausen-like switching-current jumps in Se-doped InAs/Al nanowire Josephson junctions under low perpendicular magnetic fields.
• The paper employs comprehensive four-wire transport measurements, effective field modeling, and random-field Ising model simulations to characterize the discrete magnetization reconfigurations.
• The paper rules out alternative mechanisms such as Zeeman-induced 0–π transitions and highlights potential applications in reconfigurable superconducting devices.

Magnetically Induced Switching-Current Jumps in InAs/Al Josephson Junctions

Device Architecture, Materials, and Experimental Approach

The study presents experimental evidence of abrupt, Barkhausen-like switching-current jumps in $n$-doped InAs/Al nanowire (NW) Josephson junctions (JJs) under low, perpendicular magnetic fields. The devices consist of Se-doped InAs NWs (diameter $\sim$80–90 nm, length $\sim$1.5 μm) grown by Au-catalyzed chemical beam epitaxy and contacted with Ti/Al (10/100 nm) electrodes with interelectrode separation $L \approx 70$ nm. The four-wire transport measurements are performed at temperatures ranging from 30 mK up to 900 mK, using a perpendicular magnetic field as the control parameter.

Figure 1: Schematic of the InAs/Al NW JJ, false-colour SEM of the junction, and $V$-$I$ characteristic at $T=30$~mK with switching current $I_\mathrm{sw}$.

Device preparation includes ammonium polysulfide treatment to remove the native oxide from the NW prior to metal deposition. The $V$–$I$ characteristics exhibit pronounced switching and retrapping features, consistent with underdamped JJ dynamics.

Magnetic Interference Phenomena and Switching-Current Discontinuities

The signature experimental observation is a modulation of the switching current $\sim$0 as a function of out-of-plane magnetic field, displaying a central Fraunhofer-like envelope with an abrupt ($\sim$10.13 μA) transition at $\sim$2 3 mT, separating two distinct switching-current branches.

Figure 2: Differential resistance map $\sim$3 at 30 mK, showing the superconducting to resistive transition and abrupt $\sim$4 jumps; $\sim$5 at various $\sim$6, with central Fraunhofer-like modulation and discrete switching-current jumps, cartooning the underlying local domain reconfigurations.

Classically, $\sim$7 follows a Fraunhofer pattern due to interference of supercurrents with phase winding proportional to the local flux, with enhanced focusing effects caused by the device geometry and the thin-film nature of the Al contacts. The robustness of the observed discontinuity, its reproducibility in both magnetic field sweep directions, and manifestation across different devices confirm the nontrivial, intrinsic origin of the effect.

The threshold field for the switching-current jump ($\sim$8 mT) displays negligible temperature dependence up to 900 mK, contrasting with the monotonic suppression of the superconducting critical field ($\sim$9) with increasing $\sim$0, as expected for thin Al contacts.

Figure 3: (a) $\sim$1 (parabolic fits), (b) $\sim$2 (temperature-independent at $\sim$3~mT), (c) Jump amplitude $\sim$4 vs $\sim$5.

Hysteresis, Metastability, and Field Sweep Protocols

A pronounced sweep-direction hysteresis emerges in the $\sim$6 maps, with the principal $\sim$7 jump near $\sim$8 mT and smaller additional discontinuities occurring at device- and sweep-history-dependent fields. This reflects the presence of metastable domain configurations and avalanche-like dynamics, as expected for Barkhausen-type switching in magnetically disordered systems.

Figure 4: $\sim$9 maps for opposite sweep directions showing main and secondary switching-current jumps, highlighting metastability and history dependence.

Simultaneous observation across multiple devices underlines the generality of the phenomenon.

Figure 5: $L \approx 70$0 for three devices, all showing Fraunhofer-like modulation plus abrupt jumps, underlining device-to-device reproducibility.

Flux Focusing, Effective Field Modeling, and Domain Contributions

Device geometry induces strong flux focusing, enhancing the effective field at the weak link. This is accounted for by a focusing parameter $L \approx 70$1, derived from lithography and thin-film penetration considerations ($L \approx 70$2).

Figure 6: Schematic showing geometry for flux focusing calculations with effective dimensions.

The authors propose an effective-field perspective:

$L \approx 70$3

where $L \approx 70$4 encapsulates the influence of a local magnetically active texture or domain arrangement. In this framework, Barkhausen-like jumps in $L \approx 70$5 result in discrete $L \approx 70$6 shifts, directly reshaping the interference response and resulting in the observed $L \approx 70$7 jumps.

The switching dynamics and metastable avalanche physics are captured via a quasi-adiabatic, zero-temperature random-field Ising model (RFIM) for discrete domain flips, including finite anisotropy and disorder. Numerical implementations based on strip-like geometries show magnetization response curves with reproducible, step-like jumps mirroring experimental $L \approx 70$8 discontinuities.

Figure 7: (a) Cartoon of NW domain arrangement; (b) RFIM magnetization curve under quasi-adiabatic sweep showing stepwise transitions analogous to Barkhausen jumps.

These results support a phenomenology where discrete, metastable reconfigurations of local magnetic domains are responsible for the sharp current switching features, rather than superconducting-vortex trapping, which would not account for the observed temperature independence or robust scan-to-scan reproducibility.

Exclusion of Zeeman-Induced 0–$L \approx 70$9 Transition and Alternative Mechanisms

Alternative explanations, such as Zeeman-induced $V$0–$V$1 phase transitions or vortex entry, are quantitatively ruled out. Estimated Zeeman-field scales required for a $V$2–$V$3 transition in InAs NWs are at least several tesla, orders of magnitude larger than the observed $V$4 mT threshold. Flux trapping and conventional Abrikosov vortex physics would also yield strong temperature dependence and irreproducible switching, in disagreement with experiment.

Theoretical and Practical Implications

This work demonstrates that InAs/Al JJ devices function as highly sensitive interferometric probes of intrinsic, mesoscopic magnetic reconfigurations. The observation of Barkhausen-type switching-current jumps at millitesla fields reveals that even in homogeneous semiconductor–superconductor hybrids, local magnetically active domains or surface moments (not explicitly engineered ferromagnetic inclusions) can play a pivotal role in the Josephson transport landscape.

On the practical side, these findings suggest new avenues for phase-controlled superconducting devices, with potential applications in reconfigurable superconducting memories, logic, and multiterminal hybrid architectures with field-/history-tunable characteristics. Further, the results make a strong case for the role of intrinsic disorder or inhomogeneity in the design and interpretation of nanowire superconducting hybrids, especially regarding topological or spin-orbit phenomena.

Conclusion

The study provides definitive evidence for magnetically induced, Barkhausen-type switching-current jumps in InAs/Al nanowire Josephson junctions. Experimental results, phenomenological modeling, and exclusion of standard superconducting mechanisms support an interpretation in terms of avalanche-like, metastable reconfiguration of magnetic domains coupled to the weak link. This physics introduces history dependence and discrete, robust current switching features within otherwise conventional Fraunhofer-like interference patterns. These results broaden the understanding of magnetism–superconductivity interplay in hybrid systems and motivate the exploration of controllable, switchable Josephson functionality for quantum and classical device engineering.

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