Local suppression of Josephson currents in niobium/two-dimensional electron gas/niobium structures by an injection current

Abstract

We investigated niobium-AlGaSb/InAs-niobium hybrid structures using a high mobility two-dimensional electron gas as a weak link. The Josephson current observed in this structure was suppressed by an injection current driven into the weak link via an additional normal lead. Using a four-terminal configuration the supercurrent is suppressed all over the weak link. In a three-terminal configuration it was possible to suppress the supercurrent locally. ͓S0163-1829͑99͒06217-7͔The semiconductor/superconductor hybrid structure has been the subject of extensive research during the last years, to prove its suitableness as an interface between superconductor and semiconductor electronics. Especially the control of the supercurrent in a weak-link structure has attracted considerable interest in recent years. 1 One approach was to transfer the well-known semiconductor field effect transistor to superconductor/two-dimensional electron gas ͑2DEG͒ structures as proposed by Clark et al. 2 The supercurrrent flowing through the 2DEG was switched off by reducing the coherence length in the channel by applying a negative gate voltage. 3,4 Since the voltage necessary for depleting the electrons in the 2DEG channel is typically of the order of the band gap of the semiconductor and the output signal of the order of the superconducting gap of the electrodes, a voltage gain is hard to achieve. An alternative concept to avoid this problem is controlling the supercurrent by the injection of electrons via an additional nonsuperconductive contact into the weak link. [5][6][7][8] The energy of these carriers should be only of the order of the superconducting gap of the electrodes. Very recently, the control of the supercurrent by an injection current was experimentally succeeded for a Nb/Au weak link structure. 9 This system was in the diffusive regime with inelastic scattering processes thermalizing the injected carriers.In our current-controlled structure the superconductor Nb was contacted to a high-mobility two-dimensional electron gas ͑2DEG͒ in an Al 0.2 Ga 0.8 Sb/InAs heterostructure. Due to the high electron mobility the carrier transport from one Nb electrode to the opposite one can be considered to be ballistic. In addition inelastic scattering should become relevant only for higher temperatures. For weak links without inelastic scattering an even more efficient tuning of the Josephson current was predicted compared with the case of inelastic scattering present. 10 It will be shown that if a current is injected via Ohmic contacts into the 2DEG in a four-terminal configuration the supercurrent can be suppressed completely. In a three-terminal configuration it was possible to suppress the supercurrent locally, which was proven by measuring and fitting the interference patterns of the Josephson current appearing when a magnetic field is applied to the weak link.The heterostructure which forms the weak link in our structure was grown by molecular-beam epitaxy on a semiinsulating GaAs substrate. After a 1100 nm Al-Ga-Sb buffer layer, a 5...

Opportunities for mesoscopics in thermometry and refrigeration: Physics and applications

“…In controllable Josephson junctions, the supercurrent is modulated by driving the quasiparticle distribution out of equilibrium ͑van Wees et al, 1991;Volkov, 1995;Volkov and Pavlovskii, 1996;Volkov and Takayanagi, 1997;Wilhelm et al, 1998;Yip, 1998;Seviour and Volkov, 2000a;Heikkilä et al, 2002͒ via dissipative current injection in the weak link from additional normal-metal terminals. This operation principle leads to a controlled supercurrent suppression and was successfully exploited in both all-metal ͑Morpurgo et Baselmans et al, 1999Baselmans et al, , 2001aBaselmans et al, , 2001bShaikhaidarov et al, 2000;Baselmans, Heikkilä, et al, 2002;Huang et al, 2002͒ ͑where a transition to a state was also reported͒ as well as in hybrid semiconductor-superconductor weak links ͑Schäpers et Kutchinsky et al, 1999;Neurohr et al, 1999;Richter, 2000;Schäpers, Guzenko, et al, 2003;. The situation drastically changes if we allow current injection from additional superconducting terminals arranged in a SINIS fashion ͑Baselmans, 2002; Giazotto, Taddei, et al, 2003;Giazotto et al, 2004a.…”

“…The physical origin of the SF cooler operation stems from the spin-band splitting characteristic of a ferromagnet. The electron involved in the Andreev reflection and its phase-matched 4 See, for example, Kastalsky et al, 1991;Nguyen et al, 1992;van Wees et al, 1992;Xiong et al, 1993;Bakker et al, 1994;Magnée et al, 1994;Nitta et al, 1994;Kutchinsky et al, 1997;Poirier et al, 1997;Badolato et al, 2000;Giazotto, Cecchini, et al, 2001;Giazotto, Pingue, et al, 2003;2001. FIG.…”

Nonequilibrium Josephson current in ballistic multiterminal SNS junctions

“…It is assumed that all transverse modes couple equally to the modes in the injection point contact. [12] Boundary conditions are incoming electron and hole quasiparticles from the normal reservoir and incoming electron-and hole-like quasiparticles from the superconductors at energies above the gap. Knowing the wave function coefficients the current density is straightforwardly calculated.…”

Current-injection in a ballistic multiterminal superconductor/two-dimensional electron gas Josephson junction

“…12 In most experimental situations the distribution function will be in between both extreme limits. 2,3 In this report we discuss the carrier injection into a ballistic superconductor/two-dimensional electron gas multiterminal junction. The 2DEG is located in a strained InGaAs/ InP layer.…”

“…In addition, control of a supercurrent was also observed in ballistic junctions with a high mobility twodimensional electron gas ͑2DEG͒ as an N layer. [2][3][4] Control of a supercurrent by coupling a normal reservoir via a constriction to a ballistic SNS junction was first proposed by van Wees et al 5 Further theoretical studies on ballistic nonequilibrium junctions dealt with the anomalous dc Josephson current, 6,7 four-terminal junctions, 8,9,7 and Andreev level spectroscopy. 10 The current injection into a diffusive junction was first discussed by Volkov.…”