Josephson Field-Effect Transistors Based on All-Metallic Al/Cu/Al Proximity Nanojunctions

Abstract

We demonstrate proximity-based all-metallic mesoscopic superconductor-normal metalsuperconductor (SNS) field-effect controlled Josephson transistors (SNS-FETs) and show their full characterization from the critical temperature T c down to 50 mK in the presence of both electric and magnetic field. The ability of a static electric field -applied by mean of a lateral gate electrode-to suppress the critical current I s in a proximity-induced superconductor is proven for both positive and negative gate voltage values. I s reached typically about one third of its initial value, saturating at high gate voltages. The transconductance of our SNS-FETs obtains values as high as 100 nA/V at 100 mK. On the fundamental physics side, our results suggest that the mechanism at the basis of the observed phenomenon is quite general and does not rely on the existence of a true pairing potential, but rather the presence of superconducting correlations is enough for the effect to occur. On the technological side, our findings widen the family of materials available for the implementation of all-metallic field-effect transistors to synthetic proximity-induced superconductors. arXiv:1903.03435v2 [cond-mat.mes-hall]

Unveiling mechanisms of electric field effects on superconductors by a magnetic field response

“…As in similar experiments [1,2,6,7,[9][10][11], the critical current can be reduced, up to complete suppression at the critical gate voltage V C…”

“…Recently, it has been shown that the superconducting (SC) properties of metallic Bardeen-Cooper-Schrieffer (BCS) superconductors can be influenced via electrostatic gating [1]. The most striking effect: reduction and suppression of the critical supercurrent, has been broadly demonstrated in metallic nanowires [2][3][4] and Dayem bridges [5][6][7][8] made of titanium, titanium nitrate, aluminum, niobium, and vanadium, as well as in aluminum-copper-aluminum Josephson junctions [9]. Moreover, recent experiments have probed the effect of electrostatic gating on the SC phase in a SQUID [10], and on the nature of the switching current distributions in gated titanium Dayem bridges [11].…”

Gate Control of Superconductivity in Mesoscopic All-Metallic Devices

“…The quenching of the supercurrent is symmetric for V G −→ −V G for bath temperatures between 20 mK and 3 K, as shown in Figure 1c. As reported in conventional experiments [2][3][4]9], widening of the plateau in which the gate voltage is not effective is visible as the temperature rises. The suppression of the supercurrent can be observed up to a temperature of 3 K, with complete suppression at |V G | = 40 V for T > 2 K. Notably, the suppression of I S is visible up to a temperature of 3 K because the gating affects a localized region of the superconductor around the constriction [24].…”

“…The dependence of I S [2][3][4][5][6]9,23,26,31] on the gate voltage is shown to acquire the I S vs. V G characteristics as a function of bath temperature. Figure 6b shows that the supercurrent vanishes for |V G | 34 V and that such a value appears to be independent from the bath temperature.…”

“…In these studies, the authors analyzed the effect of electrostatic gating, generating electric fields reaching the order of 10 8 V/m and, at the same time, creating negligible variations in the surface charge carrier concentration. Although an increase in the critical temperature of a superconducting NbN wire was reported [8], the majority of works in this field show ambipolar suppression of supercurrent, e.g., in all-metallic superconductor wires [2], nano-constriction Josephson junctions (JJs) [3,4], fully metallic Superconducting Quantum Interference Devices (SQUID) [6], and proximity nanojunctions [9]. Such an unconventional gating effect in BCS superconductor systems is the first step in the realization of easy fabrication and high-scalable technologies in both environments of classic superconducting electronics and quantum computing.…”