The New Gate Epub

[Ilona Brownson]

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The gate theory of pain, published by Ronald Melzack and Patrick Wall in Science in 1965, was formulated to provide a mechanism for coding the nociceptive component of cutaneous sensory input. The theory dealt explicitly with the apparent conflict in the 1960s between the paucity of sensory neurons that responded selectively to intense stimuli and the well-established finding that stimulation of the small fibers in peripheral nerves is required for the stimulus to be described as painful. It incorporated recently discovered mechanisms of presynaptic control of synaptic transmission from large and small sensory afferents, which was suggested to "gate" incoming information depending on the balance between these inputs. Other important features included the convergence of small and large sensory inputs on spinal neurons that transmitted the sensory information to the forebrain as well as the ability of descending control pathways to affect the biasing established by the gate. The clarity of the model and its description gave this article immediate visibility, with numerous attempts made to test its various predictions. Although subsequent experiments and clinical findings have made clear that the model is not correct in detail, the general ideas put forth in the article and the experiments they prompted in both animals and patients have transformed our understanding of pain mechanisms.

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Early observations on Josephson diodes were interpreted in terms of φ0-shift in ballistic systems with skewed CPR18,22,23,24,56. Within this picture, the SDE ultimately originates (as it does the φ0-shift) from SOI. An alternative model, proposed by Banerjee et al.30 based on the theory of ref. 50, explains the same effect in terms of a purely orbital mechanism. To date, it is not clear yet to which extent the two mechanisms (namely, the SOI-based and the purely orbital mechanism) contribute to the supercurrent rectification observed in experiments.

In this work, we make use of an asymmetric SQUID with mutually orthogonal junctions to directly measure both the anomalous φ0-shift and the SDE on the same junction. By gating, we can electrostatically control both effects and highlight their relation. Finally, by measuring the temperature dependence of the φ0-shift and of the diode efficiency we highlight the role of the higher harmonics of the CPR for the emergence of the SDE. We comment on our results in light of alternative models proposed in the literature and compare the temperature dependence of φ0 and the SDE to the predictions of a minimal theoretical model.

The main goal of our study is to elucidate the physical mechanism behind the intrinsic SDE in single, homogeneous Josephson junctions. The effect has been so far explained by two different models: one14,18,56 is based on the combination of Rashba SOI plus Zeeman interaction (due to an external in-plane field or exchange interaction); the other is a purely orbital mechanism30,50 based on the finite Cooper pair momentum induced in the superconducting leads by the flux associated to the in-plane field30. This flux is finite if the parent superconducting film and the 2DEG are spatially separated.

The main difference between the two pictures is the expected dependence on Vg. Such dependence naturally emerges since Vg affects the band alignment and thus the Rashba coefficient αR. Both αR and the electron density n critically affect φ0, which, in turn, determines η in multichannel systems. In contrast, the orbital mechanism30 hardly depends on the gate voltage (Max Geier, Karsten Flensberg, private communication). As discussed in the Supplementary Information, the gate voltage also affects the magnetochiral anisotropy for the inductance18, an effect that is strictly related to the supercurrent rectification27. The observed strong gate dependence of φ0 and η indicates that the Rashba-based mechanism must certainly play an important role in the SDE. On the other hand, the orbital mechanism cannot be ruled out by our observations: it could still coexist with the spin-orbit-based mechanism.

Finally, we would like to stress that, even though we make use of a SQUID to link η to φ0, our point does not concern the (trivial and long known38) SDE of the asymmetric SQUID as a whole. Our focus is exclusively on the intrinsic SDE in a single, homogeneous junction (JJ2).

In conclusion, we have shown the coexistence of anomalous Josephson effect and supercurrent rectification by measuring both effects on the same Josephson junction embedded in a SQUID. The observed gate voltage and temperature dependence are compatible with a spin-orbit based picture where supercurrent rectification arises in multichannel junctions with anomalous shift φ0 and skewed current-phase relation.

Josephson diodes based on φ0-junctions are important for both fundamental research and applications, e.g. as sensors for readout of racetrack memory devices67,68. They are novel and powerful probes of symmetry breaking in 2D superconductors21,49,69 and possible probes of topological phase transitions39. A recent proposal70 suggested that the anomalous Josephson effect might be used in multiterminal junctions to obtain compact nonreciprocal devices as, e.g., circulators for rf-applications71.

A circuit model of the asymmetric SQUID device, which includes the effect of inductive screening in the loop and the reference junction is described in the Supplementary Information. The model can reproduce the experimentally found Ic(Bz) curves when using realistic parameters for the kinetic inductance of the aluminum electrodes. A detailed discussion of the model and simulation results are provided in the Supplemental Information. The most important findings from the simulations regarding our data evaluation are:

where the sum over n ensures to account for the current contributions of all bound states (i.e., from all transverse channels of the junction) and kB indicates the Boltzmann constant. The current at zero temperature can, in the simplest case, be extracted from the thermodynamic relation74

S.R., T.A. and J.B. fabricated the devices and performed initial transport characterization of the hybrid superconductor/semiconductor wafer. S.R. and T.A. performed the measurements with the SQUID device. S.R., C.S. and N.P. conceived the experiment. A.C., D.K. and J.F. formulated the theoretical model. A.C. performed the numerical simulations of the temperature dependence of the SDE and φ0. N.P., S.R., C.S., A.C. and D.K. wrote the manuscript. T.L., S.G. and G.C.G. designed the heterostructure and conducted MBE growth. S.R., T.A. and N.P. analyzed the data. M.J.M. supervised research activities at Purdue.

Achim Seidel was born in Stuttgart, Germany, 1986. He received his B.Eng. degree in mechatronics/electrical engineering from the University of Applied Sciences Esslingen, Esslingen, Germany, in 2010. In 2012, he received the M.Sc. degree from Reutlingen University, Reutlingen, Germany. Between 2012 and 2019, Achim Seidel was working as a research assistant at the Robert Bosch Center for Power Electronics at Reutlingen University, Reutlingen, Germany. He received the Ph.D. degree (Summa Cum Laude) from Leibniz University Hannover, Germany, in 2020. Since 2019, he is a hardware developer for ebike chargers at the Robert Bosch GmbH in Reutlingen, Germany.

Bernhard Wicht has 20+ years of experience in analog and power management IC design. He received the Dipl.-Ing. degree in electrical engineering from University of Technology Dresden, Germany, in 1996 and the Ph.D. degree (Summa Cum Laude) from University of Technology Munich, Germany, in 2002. Between 2003 and 2010, he was with Texas Instruments, Freising, responsible for the design of automotive power management ICs. In September 2010, he became a full professor for integrated circuit design and a member of the Robert Bosch Center for Power Electronics at Reutlingen University, Germany. Since April 2017, he has been heading the Chair for Mixed-Signal IC Design at Leibniz University Hannover, Germany. His research interest includes IC design with focus on power management, gate drivers and high-voltage ICs. Dr. Wicht was co-recipient of the 2015 ESSCIRC Best Paper Award and of the 2019 First Prize Paper Award of the IEEE Journal of Emerging and Selected Topics in Power Electronics. In 2018, he received the faculty award for excellent teaching at his university. He invented seventeen patents with several more pending. He is currently a member of the Technical Program Committee of ISSCC and he is also a Distinguished Lecturer of the IEEE Solid-State Circuits Society.

ISO/TS 19870:2023 is a technical specification on methodologies for determining the greenhouse gas (GHG) emissions associated with the production, conditioning, and transport of hydrogen. It provides a comprehensive framework for assessing the carbon footprint of hydrogen technologies, from well to delivery gate, covering all stages of the life-cycle analysis.

This specification is critical for standardizing GHG emissions assessment across various hydrogen production pathways. It supports global climate goals by offering a transparent, consistent benchmark for evaluating and comparing hydrogen's environmental impact. This is essential for fostering trust among investors, advancing competition between hydrogen pathways based on GHG footprint, and aiding in the certification of sustainable hydrogen.

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