Coherent transport and nonlocality in mesoscopic SNS junctions: anomalous magnetic interference patterns

Abstract

We show that in ballistic mesoscopic SNS junctions the period of critical current versus magnetic flux dependence (magnetic interference pattern), I c ( ), changes continuously and nonmonotonically from 0 to 2 0 as the length-to-width ratio of the junction grows, or temperature drops. In diffusive mesoscopic junctions the change is even more drastic, with the first zero of I c ( ) appearing at 3 0 .The effect is a manifestation of nonlocal relation between the supercurrent density and superfluid velocity in the normal part of the system, with the characteristic scale, the normal metal coherence length, and arises due to restriction of the quasiparticle phase space near the lateral boundaries of the junction. It explains the 2 0 -periodicity recently observed by Heida et al. [Phys. Rev. B57, R5618 (1998)]. We obtained explicit analytical expressions for the magnetic interference pattern for a junction with an arbitrary length-to-width ratio. Experiments are proposed to directly observe the 0 → 2 0 -and 0 → 3 0 -transitions. c 1999 Academic Press Key words: nonlocality, mesoscopic, Josephson.It is well established that the electrodynamics of the superconductors is nonlocal on the scale of ξ 0 [1, 2], and so is the current-phase relation (since vector potential and superconducting phase both enter through one gauge-invariant, combination superfluid velocity). In the normal layer of an SNS system, the place of ξ 0 is taken by the normal metal coherence length, ξ T = v F /2πk B T (in the ballistic limit, L l i , where l i is the impurity scattering length),is the diffusion constant of electrons in the dirty metal [3,4]. This length can obviously greatly exceed ξ 0 at low enough temperatures, and is limited only by the inelastic scattering length in the system, l φ , which also diverges as T → 0. (The latter gives the scale of classical nonlocality in mesoscopic systems, related to †

On‐Chip Andreev Devices: Hard Superconducting Gap and Quantum Transport in Ballistic Nb–In0.75Ga0.25As‐Quantum‐Well–Nb Josephson Junctions

“…The oscillation period of I c (B) changes continuously and nonmonotonically from Φ 0 to 2Φ 0 depending on the size and topology of the devices where Φ 0 = h/2e is the flux quantum. [14][15][16][17] In our device the oscillation of I c (B) slightly differs from the Fraunhofer pattern that shows a maximum in the supercurrent at zero applied-field and its oscillatory amplitude decays to zero by increasing the field. This is because we have a junction with a length of 850 nm at the shortest path (where the supercurrent is likely to observe) that increases to 26 µm at the end of the active region (where it is unlikely to observe the phase coherent quantum transport).…”

Even-odd flux quanta effect in the Fraunhofer oscillations of an edge-channel Josephson junction

“…Turning now to the experiment that motivated this analysis [4], we first of all notice that the observed even-odd effect appears already for the first few peaks around zero field. An explanation in terms of a Lorentz-force induced asymmetry in the current distribution is therefore unlikely [19][20][21][22][23]. The h/e-periodic Josephson effect of Majorana zero modes [24] is spoiled, on the time scale of the experiment, by any small amount of quasiparticle poisoning [6], so an explanation along these lines is not viable.…”

Transport properties of Josephson systems : geometry versus topology

“…The ratio between the length L and the width W of the junctions can change both the magnitude and period of the diffraction pattern [80]. The period increases from Φ 0 to 2Φ 0 for L/W → ∞ [81] when the junction edges are 'open', as in Fig. 2.4(a).…”

“…The experimentally realised dc SQUIDs, described in chapter 5, based (a) Geometry of S-TI-S junctions as used in the calculation of Ref. [81] to determine the critical current modulation by applied magnetic fields. The dotted arrow shows the path of an electron that never goes to the other superconductor but leaves the junction.…”