"Superconductor to weak-insulator transitions in disordered Tantalum Nitride films"

Nicholas P. Breznay: Mihir Tendulkar, Li Zhang, Sang-Chul Lee, and Aharon Kapitulnik; Phys Rev B, 10/31/17.

Additional Authors: Mihir Tendulkar, Li Zhang, Sang-Chul Lee, and Aharon Kapitulnik

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 ≈ 1.3, with a corresponding critical field Hc << Hc2, the upper critical field. The Hall effect exhibits a crossing point near Hc, but with a nonuniversal critical value ρcxy 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.