  The magnetic-field-tuned quantum superconductor-insulator transitions of
disordered amorphous indium oxide films are a paradigm in the study of quantum
phase transitions, and exhibit power-law scaling behavior. For superconducting
indium oxide films with low disorder, such as the ones reported on here, the
high-field state appears to be a quantum-corrected metal. Resistance data
across the superconductor-metal transition in these films are shown here to
obey an activated scaling form appropriate to a quantum phase transition
controlled by an infinite randomness fixed point in the universality class of
the random transverse-field Ising model. Collapse of the field-dependent
resistance vs. temperature data is obtained using an activated scaling form
appropriate to this universality class, using values determined through a
modified form of power-law scaling analysis. This exotic behavior of films
exhibiting a superconductor-metal transition is caused by the dissipative
dynamics of superconducting rare regions immersed in a metallic matrix, as
predicted by a recent renormalization group theory. The smeared crossing points
of isotherms observed are due to corrections to scaling which are expected near
an infinite randomness critical point, where the inverse disorder strength acts
as an irrelevant scaling variable.
