Josephson diode effect in a ballistic single-channel nanowire (2404.01429v2)
Abstract: When time-reversal and inversion symmetry are broken, superconducting circuits may exhibit a so-called diode effect, where the critical currents for opposite directions of the current flow differ. In recent years, this effect has been observed in a multitude of systems and the different physical ingredients that may yield such an effect are well understood. On a microscopic level, the interplay between spin-orbit coupling and a Zeeman field may give rise to a diode effect in a single Josephson junction. However, so far there is no analytical description of the effect within a simple model. Here we study a single channel nanowire with Rashba spin-orbit coupling and in the presence of a Zeeman field. We show that the different Fermi velocities and spin projections of the two pseudo-spin bands lead to a diode effect. Simple analytical expressions for the diode efficiency can be obtained in limiting cases.
- The magnetic field in the leads may also affect the induced superconductivity, leading to different gaps Δ±subscriptΔplus-or-minus\Delta_{\pm}roman_Δ start_POSTSUBSCRIPT ± end_POSTSUBSCRIPT in the two pseudo-spin bands. Here we neglect this effect.
- Note that the same equations may also be used to describe an asymmetric SQUID squid1 ; squid2 , where the subscript j𝑗jitalic_j labels the two Josephson junctions in the SQUID loop and ϕj=jΦ/(2Φ0)subscriptitalic-ϕ𝑗𝑗Φ2subscriptΦ0\phi_{j}=j\Phi/(2\Phi_{0})italic_ϕ start_POSTSUBSCRIPT italic_j end_POSTSUBSCRIPT = italic_j roman_Φ / ( 2 roman_Φ start_POSTSUBSCRIPT 0 end_POSTSUBSCRIPT ) with ΦΦ\Phiroman_Φ the flux through the loop and Φ0subscriptΦ0\Phi_{0}roman_Φ start_POSTSUBSCRIPT 0 end_POSTSUBSCRIPT the flux quantum.
- One obtains the same current-phase relation when finite-momentum pairing is realized in the conventional superconducting leads fu-diode ; zazunov-diode .
- Similar results for the case Δ+=Δ−subscriptΔsubscriptΔ\Delta_{+}=\Delta_{-}roman_Δ start_POSTSUBSCRIPT + end_POSTSUBSCRIPT = roman_Δ start_POSTSUBSCRIPT - end_POSTSUBSCRIPT were obtained in Ref. topo, .
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