A Josephson junction supercurrent diode (2103.06984v1)

Abstract: Transport is called nonreciprocal when not only the sign, but also the absolute value of the current, depends on the polarity of the applied voltage. It requires simultaneously broken inversion and time-reversal symmetries, e.g., by the interplay of spin-orbit coupling and magnetic field. So far, observation of nonreciprocity was always tied to resistivity, and dissipationless nonreciprocal circuit elements were elusive. Here, we engineer fully superconducting nonreciprocal devices based on highly-transparent Josephson junctions fabricated on InAs quantum wells. We demonstrate supercurrent rectification far below the transition temperature. By measuring Josephson inductance, we can link nonreciprocal supercurrent to the asymmetry of the current-phase relation, and directly derive the supercurrent magnetochiral anisotropy coefficient for the first time. A semi-quantitative model well explains the main features of our experimental data. Nonreciprocal Josephson junctions have the potential to become for superconducting circuits what $pn$-junctions are for traditional electronics, opening the way to novel nondissipative circuit elements.

• The paper introduces a superconducting diode effect using Josephson junctions on InAs quantum wells, achieving dissipationless nonreciprocity in supercurrents.
• Numerical simulations based on Bogoliubov–de Gennes equations and Kwant confirm that asymmetric current-phase relations yield measurable magnetochiral anisotropy.
• The findings pave the way for quantum circuit applications by enabling nondissipative elements essential for quantum computing and superconducting spintronics.

Insights into a Josephson Junction Supercurrent Diode

The paper "A Josephson Junction Supercurrent Diode" explores the development of a novel superconducting diode using Josephson junctions (JJs) fabricated on InAs quantum wells. The research bridges a gap in nonreciprocal transport technologies by providing a method to achieve dissipationless nonreciprocity in superconducting circuits, which could be as transformative for quantum technologies as the p-n junction has been for conventional electronics.

Experimental Findings and Their Theoretical Basis

The authors have engineered JJs that exhibit nonreciprocal supercurrent behavior, a significant advancement considering previous studies were limited to nonreciprocal resistive elements. This is achieved by fabricating JJs on InAs quantum wells, which incorporate spin-orbit coupling and under certain magnetic field conditions, break both inversion and time-reversal symmetries. As such, these JJs enable supercurrent rectification well below the superconducting transition temperature, T_c.

Key observations include the asymmetry in supercurrent due to changes in the Josephson inductance measured across different biases, revealing a magnetochiral anisotropy. This anisotropy was directly measured and quantified as a supercurrent magnetochiral anisotropy coefficient for the first time, aligning well with theoretical predictions provided by a semi-quantitative model introduced in the paper. This model accurately describes the nonreciprocal behavior via modulation of the current-phase relation (CPR) for the JJs, which is influenced by external magnetic fields and intrinsic Rashba spin-orbit interactions.

Numerical Analysis and Experimental Correlation

The work presents a robust numerical simulation using a theoretical framework based on Bogoliubov-de Gennes equations and Kwant, a software package designed for quantum transport calculations. It elucidates how the nonsinusoidal nature of the CPR and parity-breaking components of the supercurrent lead to supercurrent rectification. This aspect of the JJ's functionality parallels that of traditional diodes in electronic circuits and is confirmed experimentally by supercurrent interference patterns revealing consistent critical current differences in opposite current directions.

Comparison and Implications

The paper also makes a comparison between supercurrents deep in the superconducting phase and near the transition temperature, indicating similar magnitudes of magnetochiral anisotropy coefficients. This finding suggests that the role of spin-orbit coupling must be coupled with the influence of confinement potentials, providing a complex interaction network that governs the nonreciprocal supercurrent behavior.

The implications of this research extend into the field of nondissipative circuit elements operating under quantum principles. Such elements could yield transformative advancements in superconducting technologies, notably in the construction and design of future quantum computing systems and superconducting spintronic devices. The groundwork laid forth by exploring such diode territories within superconducting materials opens possibilities for further material exploration and device miniaturization, enhancing the efficiency and capabilities of quantum technological applications.

Conclusion and Future Insights

In conclusion, the integration of highly-transparent JJs with strategic use of magnetic fields and spin-orbit interactions allow for previously elusive supercurrent diode effects. The findings not only herald a potential cornerstone for future superconducting circuits but also invite a deeper investigation into analogous systems that fuse spin properties with superconducting phenomenon. As such, further developments in this field could unveil even more sophisticated applications in quantum information processing, where nonreciprocal elements play a crucial role in system robustness and performance.