Phase fluctuations in conventional superconductors

Area of Science:

• Condensed Matter Physics
• Superconductivity

Background:

• Bardeen-Cooper-Schrieffer (BCS) theory primarily focuses on the pairing energy scale (Δ) for superconductivity.
• Superfluid phase stiffness (J) is typically orders of magnitude larger than Δ in conventional superconductors and often overlooked.

Purpose of the Study:

• To review recent experimental developments in studying phase fluctuations in conventional superconductors.
• To highlight situations where phase stiffness (J) becomes comparable to or smaller than the energy gap (Δ).

Main Methods:

• Review of experimental findings on phase fluctuations.
• Analysis of superconducting properties under varying temperature and magnetic fields.

Main Results:

• Phase fluctuations significantly influence superconducting properties when J is comparable to or smaller than Δ.
• Novel electronic states emerge where pairing signatures persist despite the loss of zero resistance.
• Low carrier density, disorder, low dimensions, and granular structures can reduce J relative to Δ.

Conclusions:

• Phase fluctuations play a crucial role in unconventional superconducting regimes.
• Understanding phase stiffness is essential for comprehending superconductivity beyond standard BCS theory.
• Experimental studies reveal the complex interplay between phase fluctuations and superconducting properties.