Charge Berezinskii-Kosterlitz-Thouless transition in superconducting NbTiN films

Area of Science:

• Condensed Matter Physics
• Quantum Materials
• Low-Temperature Physics

Background:

• Charge-vortex duality is a theoretical concept predicting a specific transition in 2D superconductors.
• The charge Berezinskii-Kosterlitz-Thouless (BKT) transition on the insulating side of the superconductor-insulator transition (SIT) has remained experimentally unconfirmed for decades.
• This duality suggests a superinsulating state with zero conductance at finite temperatures.

Purpose of the Study:

• To experimentally observe and confirm the charge BKT transition.
• To investigate the superconductor-insulator transition (SIT) in thin films.
• To explore the properties of the predicted superinsulating state.

Main Methods:

• Fabrication of 10 nm thick NbTiN films.
• Measurement of temperature and magnetic field dependent resistance.
• Analysis of critical behavior to identify BKT transition.
• Mapping the magnetic field dependence of the charge BKT critical temperature.
• Investigating the role of electrostatic screening length.

Main Results:

• Observation of the charge BKT transition on the insulating side of the SIT.
• Identification of BKT critical behavior in the resistance.
• Mapping the magnetic field dependence of the charge BKT critical temperature.
• Characterization of the divergence of electrostatic screening length near the SIT.

Conclusions:

• The experimental observation validates the existence of the charge BKT transition.
• This study provides evidence for the superinsulating state predicted by charge-vortex duality.
• The findings deepen the understanding of quantum phase transitions in thin-film superconductors.