3D-XY critical fluctuations of the thermal expansivity in detwinned YBa2Cu3O7-d single crystals near optimal doping

TL;DR

This study uses high-resolution measurements to confirm that superconducting fluctuations in detwinned YBa2Cu3O7-d crystals near optimal doping follow the 3D-XY universality class, highlighting critical behavior over a wide temperature range.

Contribution

It provides direct experimental evidence of 3D-XY critical fluctuations in YBa2Cu3O7-d, without background subtraction, over a broad temperature region near Tc.

Findings

Critical fluctuations are observed over ±10 K around Tc.

Amplitude ratio A+/A- is approximately 0.9-1.1.

Scaling exponent |alpha| is less than 0.018.

Abstract

The strong coupling of superconductivity to the orthorhombic distortion in YBa2Cu3O7-d makes possible an analysis of the superconducting fluctuations without the necessity of subtracting any background. The present high-resolution capacitance dilatometry data unambiguously demonstrate the existence of critical, instead of Gaussian, fluctuations over a wide temperature region (+/- 10 K) around Tc. The values of the amplitude ratio A+/A-=0.9-1.1 and the leading scaling exponent |alpha|<0.018, determined via a least-squares fit of the data, are consistent with the 3D-XY universality class. Small deviations from pure 3D-XY behavior are discussed.