Superconducting phase transition in inhomogeneous chains of superconducting islands

TL;DR

This paper investigates how inhomogeneity in one-dimensional chains of superconducting islands affects their transport properties, revealing non-monotonous resistance behavior and potential quantum phase transitions driven by magnetic fields.

Contribution

It demonstrates the impact of critical temperature fluctuations on transport in inhomogeneous superconducting chains and predicts a quantum transition in the zero-temperature limit.

Findings

Resistance peaks at partial superconductivity in the chain

Inhomogeneity causes non-monotonous temperature and magnetic field dependence

Potential for zero-temperature quantum phase transition under magnetic field

Abstract

We study one dimensional chains of superconducting islands with a particular emphasis on the regime in which every second island is switched into its normal state, thus forming a superconductor-insulator-normal metal (S-I-N) repetition pattern. As is known since Giaever tunneling experiments, tunneling charge transport between a superconductor and a normal metal becomes exponentially suppressed, and zero-bias resistance diverges, as the temperature is reduced and the energy gap of the superconductor grows larger than the thermal energy. Here we demonstrate that this physical phenomenon strongly impacts transport properties of inhomogeneous superconductors made of weakly coupled islands with fluctuating values of the critical temperature. We observe a non-monotonous dependence of the chain resistance on both temperature and magnetic field, with a pronounced resistance peak at temperatures at which some but not all islands are superconducting. We explain this phenomenon by the inhomogeneity of the chains, in which neighboring superconducting islands have slightly different critical temperatures. We argue that the Giaever's resistance divergence can also occur in the zero-temperature limit. Such quantum transition can occur if the magnetic field is tuned such that it suppresses superconductivity in the islands with the weaker critical field, while the islands with stronger energy gap remain superconducting. In such a field, the system acts as a chain of S-I-N junctions.