News & Seminars | HKUST Department of Physics

Abstract

Nonreciprocal phenomena are attracting much attention as the novel probe and functionality of noncentrosymmetric materials. Among them, superconducting diode effect (SDE), a phenomenon where a superconductor's critical current becomes nonreciprocal, has attracted significant interest since its report in a Nb/V/Ta superlattice [1]. SDE is important both from both fundamental and applicational viewpoints. Thus, it is an important issue to identify its mechanisms.

In this talk, we first discuss an intrinsic mechanism to trigger SDE, emphasizing its relation to the finite-momentum superconductivity [2]. To achieve the nonreciprocity, it is required to break both the inversion and time-reversal symmetries of the system, and thus a natural platform is the noncentrosymmetric superconductors in the applied magnetic field. In such systems, it is known that helical superconductivity is realized, where Cooper pairs spontaneously acquire a finite center-of-mass momentum. We point out that the evolution of helical Cooper pairs as increasing the magnetic field is faithfully reflected into the SDE, in particular through its sign reversal. Thus, SDE can be used as the probe of helical superconductivity, which has been sought after for a long time.

Next, we discuss another strategy to trigger SDE, by using the effective time-reversal-symmetry breaking by dissipation [3]. In such a case, the diode efficiency can reach the ideal value of 100%, since the system is driven out of equilibrium. We present a minimal model to probe the concept, where we consider in-plane critical currents of superconducting thin films. We apply the perpendicular electric fields, which can enter the superconductor and cause dissipation by assuming the film thickness thinner than a length scale comparable to or larger than the coherence length. We obtain steady states by solving time-dependent Ginzburg-Landau equations and show that the SDE and the 100% SDE, which we name unidirectional superconductivity, are indeed realized in this model by the dissipation.

References

[1] F. Ando, et al., Nature, 584, 373 (2020).
[2] A. Daido, Y. Ikeda, and Y. Yanase, PRL 128, 037001 (2022).
[3] A. Daido and Y. Yanase, arXiv:2310.02539.

Please contact phweb@ust.hk should you have questions about the talk.