Nonlocal correlations in a proximity-coupled normal-metal

Abstract

We report evidence of large, nonlocal correlations between two spatially separated normal metals in superconductor/normal-metal (SN) heterostructures, which manifest themselves as nonlocal voltage generated in response to a driving current. Unlike prior experiments in SN heterostructures, the nonlocal correlations are mediated not by a superconductor, but by a proximity-coupled normal metal. The nonlocal correlations extend over relatively long length scales in comparison to the superconducting case. At very low temperatures, we find a reduction in the nonlocal voltage for small applied currents that cannot be explained by the quasiclassical theory of superconductivity, which we believe is a signature of new long-range quantum correlations in the system.

Nonlocal superconducting quantum interference device

“…However, this is for a wire with no additional normal metal leads. Experimentally, by measuring the saturation value of I c at low temperatures, we have found that E c is reduced by a fac-tor of about 20 from its expected value based on L. [25,31] This can be thought of as an increase in the effective value of L due to the increased probability of quasiparticle diffusion in the leads. Consequently, while E c ∼ 55 µeV for a length L = 450 nm and D = 170 cm 2 /s, we have used a value of 2.7 µeV, adjusting the values of ∆ and T which are specified in units of E c accordingly.…”

“…[25] Consequently, R 21,76 also shows a sharp drop at the same values of I b . As |I b | is increased further, both nonlocal differential resistances approach their normal state values (modulated by the current distribution of the quasiparticle currents), positive for R 21,35 and negative for R 21,76 , the difference in sign being due to the relative orientation of the their respective voltage leads.…”

“…This behavior in a linear structure has been verified by experiment. [25] Now consider two such SNS junctions in a dc SQUID, with additional normal metal leads attached to one, as shown in Fig. 1(c).…”