Abstract
Three decades after the prediction of charge-vortex duality in the critical vicinity of the two-dimensional superconductor-insulator transition (SIT), one of the fundamental implications of this duality—the charge Berezinskii-Kosterlitz-Thouless (BKT) transition that should occur on the insulating side of the SIT—has remained unobserved. The dual picture of the process points to the existence of a superinsulating state endowed with zero conductance at finite temperature. Here, we report the observation of the charge BKT transition on the insulating side of the SIT in 10 nm thick NbTiN films, identified by the BKT critical behavior of the temperature and magnetic field dependent resistance, and map out the magnetic-field dependence of the critical temperature of the charge BKT transition. Finally, we ascertain the effects of the finite electrostatic screening length and its divergence at the magnetic field-tuned approach to the superconductor-insulator transition.
Highlights
In the early 1970s, Vadim Berezinskii[1], Michael Kosterlitz, and David Thouless[2,3] introduced the idea of a topological phase transition in which pairs of bound vortex excitations unbind at a critical temperature TBKT
Focusing on the behavior of the thinnest film (d = 10 nm), where the degree of disorder permits fully tuning the sample with experimentally-accessible magnetic fields, we note first that the global coherent superconducting state is not achieved at lowest temperatures
The appearance of such vortices in the absence of a magnetic field is a fundamental feature of the BKT transition, which revolves around thermal fluctuations inducing vortex-antivortex pairs
Summary
In the early 1970s, Vadim Berezinskii[1], Michael Kosterlitz, and David Thouless[2,3] introduced the idea of a topological phase transition in which pairs of bound vortex excitations unbind at a critical temperature TBKT. Focusing on the behavior of the thinnest film (d = 10 nm), where the degree of disorder permits fully tuning the sample with experimentally-accessible magnetic fields, we note first that the global coherent superconducting state is not achieved at lowest temperatures.
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