Critical-Exponent Measurements of a Two-Dimensional Superconductor

Voltage-current measurements of an amorphous indium/indium-oxide thin-film composite have yielded values for the exponent $\eta \mathrm{}\left(T\right)\mathrm{}$ describing the power-law decay of the order-parameter correlation function appropriate to the Kosterlitz-Thouless description of phase transitions in two-dimensional systems. A pronounced crossover in the characteristics at the phase-transition temperature is obtained. Theoretical expressions both above and below $T_c$ are verified, and a value of $\eta \left(T_c\right)=0.23\mathrm{}$ is measured for a film with normal-state sheet resistance of 3560 Ω/□ measured at 8 K.