Current-voltage characteristics of semiconductor-coupled superconducting weak links with large electrode separations

Abstract

We have studied the current-voltage characteristics of superconducting weak links in which the coupling medium is the 2-D electron gas in InAs-based semiconductor quantum wells, with relatively large (typically 0.5µm) separations between niobium electrodes. The devices exhibit Josephson-like current-voltage characteristics; however, the falloff of the differential resistance with decreasing temperature is thermally activated, and is orders of magnitude slower than for more conventional weak links. Most unexpectedly, the thermal activation energies are found to be proportional to the width of the device, taken perpendicular to the current flow. This behavior falls outside the range of established theories; we propose that it is a fluctuation effect caused by giant shot noise associated with multiple Andreev reflections. The possibility of non-equilibrium effects is discussed.

Proximity effect, Andreev reflections, and charge transport in mesoscopic superconducting/semiconducting heterostructures

“…iii) The zero-bias differential resistance dV /dI| V =0 increases (and the current decreases) with temperature. These points of qualitative agreement between experiment and theory support the view of Thomas et al that multiple Andreev reflections are responsible for the observed nonequilibrium effects [12]. The characteristic shape of the CVC described in ii) has been also observed for a single SNS junction by Kroemer et al [10].…”

“…For the numerical computation of the proximityinduced pair potential and the current-voltage characteristics we use system parameters similar to the ones reported by the Kroemer group [9,10,12]. We assume that the InAs channel extends in x-direction over 15 nm (thickness L x ), and in z-direction the extensions of the insulating layers between the Nb electrodes, 2a, and of the Nb electrodes themselves, D − a, are about 500nm.…”

“…One observes peculiar (subgap) structures [5]- [7], [9]- [12] and spikes [11] in the differential resistances, and current-voltage characteristics (CVCs) show first a steep rise of the current, then a plateau and finally a linear current increase with "high" voltages [10,12]. The observed phenomena are interpreted in terms of Andreev reflections [5]- [12]. Nitta et al [7,8] assume that the spatially varying pair potential, required for these reflections, is induced in the InAs by the proximity effect.…”

Search for Majorana Fermions in Multiband Semiconducting Nanowires

“…Then, the single-particle Hamiltonian takes the usual form for the 2D SM in the presence of the spin-orbit Rashba interaction ( = 1):where m * , α and µ are the effective mass, the strength of spin-orbit interaction and chemical potential, respectively. The latter can be controlled using the gate electrodes [11,13]. The last term in Eq.(2) corresponds to the Zeeman term due to the applied external magnetic field aligned along thex-axis, V x = g SM µ B B x /2.…”

Nonequilibrium superconductivity in mesoscopic Nb/InAs/Nb junctions

“…The dc characteristics of the gratings have been studied extensively and published elsewhere [8]; in this article we show only dc characteristics of the single junctions. …”