Properties of n × n square arrays of proximity effect bridges

Abstract

We have studied the I-V characteristics, the dc resistance at the origin R(T), and the critical current It(T) of arrays consisting of n • n (n = 10, 20, 30, and 40) In squares separated by Au/In regions. The superconducting squares have side ds(In) from 7.5 to 15 tzm and dN(Au/In) from 2.5 to 11 ~m. These devices show two transition temperatures in their R(T) curve; one at Tcc near Tc(In) and another one at T* above Tc(Au/In). The I-V curves for each temperature region resemble recent published results on NbN granular films. These arrays follow a formalism proposed by Wolf, Gubser, and Imry to describe the transition to a resistanceless state at T*. The measured values of I~(T) are larger than expected from n noninteracting Bardeen-Johnson functions in parallel, although the exponential behavior in temperature is followed. They are compatible with the idea of bands in the quasiparticle spectrum in the Au/In regions. Deviations in I~(T) from an exponential behavior in T near T* have been analyzed by applying to SNS arrays ideas developed for phase transitions in SIS arrays. Evidence that at T* we may be observing a phase transition at Tcj due to the Josephson coupling between In squares exists but it needs the development of theoretical work to be put on more solid grounds.

The Berezinskii–Kosterlitz–Thouless Transition in Superconductors

“…These arrays were considerably larger than the similar structures of In dots on a Au/In plane studied by Sanchez and Berchier. 23 The narrow layer of Sn between adjacent Pb disks forms a Pb-Sn-Pb junction (weak link). The Pb disks were 1300Å thick and 13 microns in diameter.…”

Fundamental studies of superconductors using scanning magnetic imaging

“…3.1.2. Superconducting wire lattices, clusters, and nano-hole arrays Two dimensional arrays of Josephson junctions [135,136,137,138,139,140] have been studied extensively, not only because they offer the possibility of studying Kosterlitz-Thouless effects [141] in an ordered 2-dimensional system, but also because of interesting effects that were predicted [142] and observed [135,136] to occur when the applied field is a rational fraction of the field required to populate each cell with a quantum of magnetic flux. Scanning magnetic microscopy has been used extensively for studying vortex trapping in two-dimensional superconducting wire networks [143,58], clusters [58], and ring arrays [144,145].…”

A review of giant correlation-length effects via proximity and weak-links coupling in a critical system: 4He near the superfluid transition

“…The arrangement of junctions to form onedimensional (with current flow parallel or serial through the array) or two-dimensional arrays is also a very active field of research. This grew out of the first studies with granular materials which are modeled as an array of 2D Josephson junctions (Deutscher et al 1974, Orr et al 1986 and has been pursued with lithographically-patterned arrays (Sanchez and Berchier 1981, Resnick et al 1981, Abraham et al 1982. The interesting physics in these arrays is the nature of the superconducting transition which is of the BKT type involving vortex unbinding (Halperin and Nelson 1979).…”