Quantum Criticality at the Superconductor-Insulator Transition Probed by the Nernst Effect

Area of Science:

• Condensed Matter Physics
• Quantum Materials Science
• Phase Transitions

Background:

• The superconductor-insulator transition (SIT) is a quantum phase transition driven by quantum fluctuations at zero temperature.
• Previous studies on SIT criticality primarily relied on transport and tunneling experiments, offering indirect insights.
• Understanding quantum fluctuations near the quantum critical point is crucial for characterizing these transitions.

Purpose of the Study:

• To directly probe quantum fluctuations across the superconductor-insulator transition (SIT).
• To investigate the behavior of quantum fluctuations near the quantum critical point using a novel experimental approach.
• To determine the critical exponents associated with the SIT.

Main Methods:

• Utilized the Nernst effect, a sensitive probe of superconducting fluctuations.
• Measured the Nernst coefficient in amorphous indium oxide films tuned through the SIT.
• Extracted the transverse Peltier coefficient (αxy) to analyze thermodynamic properties.

Main Results:

• Observed a significant Nernst signal on both superconducting and insulating sides of the SIT, peaking near the critical point.
• The transverse Peltier coefficient exhibited quantum critical scaling.
• Determined critical exponents ν≈0.7 and z≈1, consistent with a clean 2D X-Y model.

Conclusions:

• The Nernst effect effectively probes quantum fluctuations through the SIT.
• The observed scaling behavior and exponents support theoretical models for quantum phase transitions in 2D systems.
• This study provides direct experimental evidence of quantum critical behavior at the SIT.