Bosonic topological insulator intermediate state in the superconductor-insulator transition
M. C. Diamantini, A. Yu. Mironov, S.M. Postolova, Xianguo Liu, Zeyu Hao, D. M. Silevitch, Y. Kopelevich, Philip Kim, Carlo A. Trugenberger, V. M. Vinokur
Abstract
A low-temperature intervening metallic regime arising in the two-dimensional superconductor-insulator transition challenges our understanding of electronic fluids. Here we develop a gauge theory revealing that this emergent anomalous metal is a bosonic topological insulator where bulk transport is suppressed by mutual statistics interactions between out-of-condensate Cooper pairs and vortices and the longitudinal conductivity is mediated by symmetry-protected gapless edge modes. We explore the magnetic-field-driven superconductor-insulator transition in a niobium titanium nitride device and find marked signatures of a bosonic topological insulator behavior of the intervening regime with the saturating resistance. The observed superconductor-anomalous metal and insulator-anomalous metal dual phase transitions exhibit quantum Berezinskii-Kosterlitz-Thouless criticality in accord with the gauge theory.