Emerging Phenomena at a Quantum Phase Transition: the Magnetic Field-Tuned Superconductor to Insulator Transition
The magnetic-field tuned superconductor-to-insulator transition (H-SIT), along with the quantum-Hall liquid-to- insulator transitions (QHIT) are paradigmatic quantum phase transitions and among the best experimentally studied ones. While evidence continue to mount to the fact that these two phenomena are in the same universality class, key results in the QHIT were not previously identified in the case of H-SIT. Tuning the disorder of two-dimensional superconducting films, and studying the full resistivity tensor, our results show a stark difference between films exhibiting weak vs. strong disorder. In weakly disordered films, the superconducting state gives way to an "anomalous metallic phase" with a resistivity that extrapolates to a non-zero value, but with a vanishing Hall resistance. In the strong disorder limit a "true" H-SIT is observed, characterized by an emerging self-duality at the H-SIT, and the proximate insulating phase is fundamentally distinct from a conventional "Anderson insulator" in that the Hall resistance, rather than diverging, tends to a finite value as the temperature approaches zero . That these features are analogous to behaviors previously documented near the QHIT supports the existence of the correspondence between the two problems implied by the composite boson theory.  N.P. Breznay, M.A. Steiner, S.A. Kivelson, A. Kapitulnik, Proceedings of the National Academy of Sciences 113 (2016), 280.