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1. Josephson Detection of Time Reversal Symmetry Breaking s +/- is Superconductivity in SnTe Nanowires

   Trimble, C.; Wei, M. T.; Kalantre, S. S.; Yuan, N. F.; Liu, P.; Cha, J. J.; Fu, L.; Williams, J. R. (January 2019, ArXiv.org)

   Exotic superconductivity, such as high TC, topological, and heavy-fermion superconductors, often rely on phase sensitive measurements to determine the underlying pairing. Here we investigate the proximity-induced superconductivity in nanowires of SnTe, where a s±is′ superconducting state is produced that lacks the time-reversal and valley-exchange symmetry of the parent SnTe. A systematic breakdown of three conventional characteristics of Josephson junctions -- the DC Josephson effect, the AC Josephson effect, and the magnetic diffraction pattern -- fabricated from SnTe nanowire weak links elucidates this novel superconducting state. Further, the AC Josephson effect reveals evidence of a Majorana bound state, tuned by a perpendicular magnetic field. This work represents the definitive phase-sensitive measurement of novel s±is′ superconductivity, providing a new route to the investigation of fractional vortices, topological superconductivity, topological phase transitions, and new types of Josephson-based devices. 

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2. Superconducting diode effect via conformal-mapped nanoholes

   https://doi.org/10.1038/s41467-021-23077-0  

   Lyu, Yang-Yang; Jiang, Ji; Wang, Yong-Lei; Xiao, Zhi-Li; Dong, Sining; Chen, Qing-Hu; Milošević, Milorad V.; Wang, Huabing; Divan, Ralu; Pearson, John E.; et al (December 2021, Nature Communications)

   null (Ed.)

   Abstract A superconducting diode is an electronic device that conducts supercurrent and exhibits zero resistance primarily for one direction of applied current. Such a dissipationless diode is a desirable unit for constructing electronic circuits with ultralow power consumption. However, realizing a superconducting diode is fundamentally and technologically challenging, as it usually requires a material structure without a centre of inversion, which is scarce among superconducting materials. Here, we demonstrate a superconducting diode achieved in a conventional superconducting film patterned with a conformal array of nanoscale holes, which breaks the spatial inversion symmetry. We showcase the superconducting diode effect through switchable and reversible rectification signals, which can be three orders of magnitude larger than that from a flux-quantum diode. The introduction of conformal potential landscapes for creating a superconducting diode is thereby proven as a convenient, tunable, yet vastly advantageous tool for superconducting electronics. This could be readily applicable to any superconducting materials, including cuprates and iron-based superconductors that have higher transition temperatures and are desirable in device applications. 

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3. Beyond the standard model of topological Josephson junctions: From crystalline anisotropy to finite-size and diode effects

   https://doi.org/10.1063/5.0214920  

   Pekerten, Barış; Brandão, David S; Bussiere, Bailey; Monroe, David; Zhou, Tong; Han, Jong E; Shabani, Javad; Matos-Abiague, Alex; Žutić, Igor (June 2024, Applied Physics Letters)

   A planar Josephson junction is a versatile platform to realize topological superconductivity over a large parameter space and host Majorana bound states. With a change in the Zeeman field, this system undergoes a transition from trivial to topological superconductivity accompanied by a jump in the superconducting phase difference between the two superconductors. A standard model of these Josephson junctions, which can be fabricated to have a nearly perfect interfacial transparency, predicts a simple universal behavior. In that model, at the same value of Zeeman field for the topological transition, there is a π phase jump and a minimum in the critical superconducting current, while applying a controllable phase difference yields a diamond-shaped topological region as a function of that phase difference and a Zeeman field. In contrast, even for a perfect interfacial transparency, we find a much richer and nonuniversal behavior as the width of the superconductor is varied or the Dresselhaus spin–orbit coupling is considered. The Zeeman field for the phase jump, not necessarily π, is different from the value for the minimum critical current, while there is a strong deviation from the diamond-like topological region. These Josephson junctions show a striking example of a nonreciprocal transport and superconducting diode effect, revealing the importance of our findings not only for topological superconductivity and fault-tolerant quantum computing but also for superconducting spintronics. 

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4. Phase jumps in Josephson junctions with time-dependent spin–orbit coupling

   https://doi.org/10.1063/5.0211562  

   Monroe, David; Shen, Chenghao; Tringali, Dario; Alidoust, Mohammad; Zhou, Tong; Žutić, Igor (July 2024, Applied Physics Letters)

   Planar Josephson junctions (JJs), based on common superconductors and III–V semiconductors, are sought for Majorana states and fault-tolerant quantum computing. However, with gate-tunable spin–orbit coupling (SOC), we show that the range of potential applications of such JJs becomes much broader. The time-dependent SOC offers unexplored mechanisms for switching JJs, accompanied by the 2π-phase jumps and the voltage pulses corresponding to the single-flux-quantum transitions, key to high-speed and low-power superconducting electronics. In a constant applied magnetic field, with Rashba and Dresselhaus SOC, anharmonic current-phase relations, calculated microscopically in these JJs, yield a nonreciprocal transport and superconducting diode effect. Together with the time-dependent SOC, this allows us to identify a switching mechanism at no applied current bias, which supports fractional-flux-quantum superconducting circuits and neuromorphic computing. 

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5. Theory of Josephson scanning microscopy with $s$ -wave tip on unconventional superconducting surface: Application to ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$

   https://doi.org/10.1103/PhysRevB.110.184519  

   Choubey, Peayush; Hirschfeld, P J (November 2024, Physical Review B)

   Josephson scanning tunneling microscopy (JSTM) is a powerful probe of the local superconducting order parameter, but studies have been largely limited to cases where the superconducting sample and superconducting tip both have the same gap symmetry—either s-wave or d-wave. It has been generally assumed that, in an ideal s-to-d JSTM experiment, the critical current would vanish everywhere, as expected for ideal c-axis planar junctions. We show here that this is not the case. Employing first-principlesWannier functions for Bi2Sr2CaCu2O8+δ , we develop a scheme to compute the Josephson critical current (Ic) and quasiparticle tunneling current measured by JSTM with subangstrom resolution. We demonstrate that the critical current for tunneling between an s-wave tip and a superconducting cuprate sample has the largest magnitude above O sites and it vanishes above Cu sites. Ic changes sign under π/2 rotation and its average over a unit cell vanishes, as a direct consequence of the d-wave gap symmetry in cuprates. Further, we show that Ic is strongly suppressed in the close vicinity of a Zn-like impurity owing to suppression of the superconducting order parameter. More interestingly, Ic acquires nonvanishing values above the Cu sites near the impurity. The critical current modulations produced by the impurity occur at characteristic wave vectors distinct from the quasiparticle interference (QPI) analog. Furthermore, the quasiparticle tunneling spectra in the JSTM setup shows coherence peaks and impurity-induced resonances shifted by the s-wave tip gap. We discuss the similarities and differences in JSTM observables and conventional STM observables, making specific predictions that can be tested in future JSTM experiments. 

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