Abstract
We have measured the current-voltage (IV) characteristics of several two-dimensional arrays of small Josephson junctions as a function of temperature, T and magnetic field B. The junctions have relatively large charging energies ≊1 K, and normal-state resistances in the range of 4–150 kΩ. From the IV characteristics we can deduce the zero-bias resistance and the threshold voltage which reveal important information about the dynamics and statics of charge solitons in the array. (T) increases with decreasing temperature and may be described by thermal activation of charge solitons, characterized by an activation energy . When the electrodes are in the normal state, is close to 1/4. At low T, the thermal activation behavior breaks down, and (T) levels off to a value that can be attributed to the quantum fluctuations in the array. This interpretation places limitations on the observability of the charge unbinding, Kosterlitz-Thouless-Berezinskii transition for single electrons. When the electrodes are superconducting, is much larger and dependent on B. In several samples, both and oscillate with B, having a period corresponding to one flux quantum per unit cell. For increasing magnetic fields, increases until B≊250–450 G where it starts to decrease rapidly. We interpret the B dependence of and as a result of competition between Cooper-pair solitons and single-electron solitons.
- Received 28 April 1994
DOI:https://doi.org/10.1103/PhysRevB.50.3959
©1994 American Physical Society