Measurements of charge soliton motion in two-dimensional arrays of ultrasmall Josephson junctions

We have measured two-dimensional arrays of Josephson junctions where the charging energy ${\mathit{E}}_{\mathit{c}}$ dominates the Josephson coupling energy ${\mathit{E}}_{\mathit{J}}$ by as much as a factor of 33. In this system, an added charge polarizes neighboring islands, creating a soliton. Instead of the predicted Kosterlitz-Thouless-Berezinskii phase transition for unbinding soliton-antisoliton pairs, we find that our linear conductance data are better described by a simple Arrhenius form, with an activation energy of ∼0.23${\mathit{E}}_{\mathit{c}}$ in the normal state and ∼0.23${\mathit{E}}_{\mathit{c}}$ plus the superconducting energy gap in the superconducting state.