Superconductor To Weak-Insulator Transitions in Disordered Tantalum Nitride Films

Nicholas P. Breznay, Mihir Tendulkar, Li Zhang, Sang-Chul Lee, and Aharon Kapitulnik

Physical Review B 96 (2017) 134522

Abstract

We study the two-dimensional superconductor-insulator transition (SIT) in thin films of tantalum nitride. At zero magnetic field, films can be disorder-tuned across the SIT by adjusting thickness and film stoichiometry; insulating films exhibit classical hopping transport. Superconducting films exhibit a magnetic-field-tuned SIT, whose insulating ground state at high field appears to be a quantum-corrected metal. Scaling behavior at the field-tuned SIT shows classical percolation critical exponents ( z ν approx 1.3 ), with a corresponding critical field ( H_c ll H_{c2} ), the upper critical field. The Hall effect exhibits a crossing point near ( H_c ), but with a nonuniversal critical value ( ρ_{xy}^{c} ) comparable to the normal-state Hall resistivity. We propose that high-carrier-density metals will always exhibit this pattern of behavior at the boundary between superconducting and (trivially) insulating ground states.

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