Crossover from time-correlated single-electron tunneling to that of Cooper pairs

TL;DR

This study investigates charge transport in a Josephson junction chain, revealing a transition from single-electron to Cooper-pair tunneling influenced by magnetic field and current, with implications for understanding quantum transport mechanisms.

Contribution

It demonstrates the crossover from electron to Cooper-pair tunneling in a Josephson junction chain as a function of magnetic field and current, highlighting incoherent Cooper-pair transport.

Findings

Single-electron tunneling dominates at high magnetic fields.

Frequency shifts from f=I/e to f=I/2e as magnetic field decreases.

Cooper-pair transport is incoherent under measured conditions.

Abstract

We have studied charge transport in a one-dimensional chain of small Josephson junctions using a single-electron transistor. We observe a crossover from time-correlated tunneling of single electrons to that of Cooper pairs as a function of both magnetic field and current. At relatively high magnetic field, single-electron transport dominates and the tunneling frequency is given by f=I/e, where I is the current through the chain and e is the electron's charge. As the magnetic field is lowered, the frequency gradually shifts to f=I/2e for I>200 fA, indicating Cooper-pair transport. For the parameters of the measured sample, we expect the Cooper-pair transport to be incoherent.