Hot-electron effects in InAs nanowire Josephson junctions

Abstract

At a superconductor (S)-normal metal (N) junction pairing correlations can "leak-out" into the N region. This proximity effect [1,2] modifies the system transport properties and can lead to supercurrent flow in SNS junctions [3]. Recent experimental works showed the potential of semiconductor nanowires (NWs) as building blocks for nanometre-scale devices [4][5][6][7], also in combination with superconducting elements [8][9][10][11][12]. Here, we demonstrate an InAs NW Josephson transistor where supercurrent is controlled by hot-quasiparticle injection from normal-metal electrodes. Operational principle is based on the modification of NW electron-energy distribution [13][14][15][16][17][18][19][20] that can yield reduced dissipation and high-switching speed. We shall argue that exploitation of this principle with heterostructured semiconductor NWs opens the way to a host of out-of-equilibrium hybrid-nanodevice concepts [7,21].One practical implementation of the present InAs-NW hot-electron Josephson transistor concept is shown in Figure 1a. The SNS junction was fabricated by e-beam lithography starting from an n-doped InAs NW (the N region, for further details see Methods) and comprises two Ti/Al superconducting electrodes placed at a distance L ≃ 60 nm (S regions). Control electrodes were fabricated by depositing two additional normal-metal Ti/Au leads at the two ends of the NW. As schematically illustrated by the overlay of Fig. 1a, the N leads are used to drive a dissipative current through the NW thereby tuning Josephson coupling in the S-NW-S structure. Figure 2a shows a set of typical IV characteristics from one of the measured S-NW-S junctions at equilibrium (i.e., V inj = 0) and at different bath temperatures T . High critical currents up to I c ≃ 350 nA (corresponding to a supercurrent density ∼ 5.5 kA/cm 2 ) are observed and Josephson coupling typically persists up to about 1 K. Furthermore, from the junction differentialresistance spectra (see Supplementary Materials) we infer a superconducting order parameter ∆ = 120 µeV and a junction normal-state resistance R N ≃ 210 Ω. The I c R N product attains values as large as ≃ 75 µeV and indicates the overall success of our junction-fabrication procedure [22]. Based on carrier-density and electronmobility values (see Methods) we estimate a momentumrelaxation length ℓ ≃ 20 nm and a diffusion coefficient D = 0.02 m 2 /s. Given the junctions geometrical length L we can estimate the Thouless-energy value, i.e., the characteristic energy scale of the N region, E Th = D/L 2 ≃ 4 meV. These values indicate that our devices can be described within the frame of the diffusive short-junction limit (L > ℓ and ∆ ≪ E Th ) [22]. Figure 2b shows the evolution of I c versus T at V inj = 0 for two representative devices D1 and D2. For comparison, the theoretical prediction for an ideal short diffusive SNS junction [22,23] is also plotted assuming for both devices a supercurrent suppression of the order of 45%. Such a suppression can be expected and probably mainly stems from a...

Magnetically-driven colossal supercurrent enhancement in InAs nanowire Josephson junctions

“…The details of the theoretical model for each fit are described in the Methods section. None of the two fitting curves can accurately describe the monotonic decay of I C ( T ) which is consistent with a junction belonging to an intermediate regime between the two above limits19, that is, L ∼ l e where l e ∼60 nm is the electron mean free path estimated in our InAs-NWs (refs 20, 29. Moreover, the diffusive fit suggests an effective junction length of the order of ∼300 nm which largely exceeds the interelectrode spacing.…”

Double quantum dot Cooper-pair splitter at finite couplings

“…The enormous advancement in the production and control of nanotubes and nanowires 11,12 opened up the possibility to couple nanosystems, in a very controlled way, to superconductors [13][14][15] taking advantage of their properties such as the spin-orbit (SO) interaction. Quantum phase transitions and anomalous current-phase relations have been studied in hybrid semiconductorsuperconductor devices.…”

Intrinsic spin-orbit interaction in diffusive normal wire Josephson weak links: Supercurrent and density of states

“…Strictly speaking this limit requires that all wire dimensions are smaller than the elastic mean free path. Typical epitaxial nanowires have mean free paths comparable to the wire thickness and much less than the wire length [16][17][18][19][20][21][22][23]. Even in this limit the diffusive-limit theory is likely to capture the essential physics much better than the fully ballistic limit.…”