  The superconductor-insulator (SI) transition in two-dimensional Ta thin films
is investigated by controlling both film thickness and magnetic field. An
intriguing metallic phase intervening superconductor and an insulator phase is
observed within a narrow range of film thickness and magnetic field. Finite
scaling analysis has been performed to investigate the nature of the SI
transition in the thickness-tuned metallic and superconducting samples. The
critical exponents in the disorder-induced metallic samples are clearly
different from the exponents obtained in the superconducting samples. Dynamical
exponent z of the superconducting samples is consistent with the theoretical
predictions (z = 1), while the exponent for the metallic samples is
approximately 0.7. The discrepancy in the transition behaviors supports that
the disorder induced metallic phase cannot be classified to the same
universality class of the superconducting Ta thin films.
