Muon spin rotation investigation of the pressure effect on the magnetic penetration depth in YBa2Cu3Ox

TL;DR

This study uses muon spin rotation to examine how pressure influences the magnetic penetration depth and superfluid density in YBa2Cu3Ox superconductors, revealing deviations from established relations and pressure-induced changes in superconducting properties.

Contribution

It introduces a new model for analyzing muSR spectra in samples with magnetic moments under pressure, and explores pressure effects on superconducting parameters in YBa2Cu3Ox.

Findings

Pressure dependence of superfluid density deviates from Uemura line.

Pressure increases superconducting gap and BCS ratio in underdoped samples.

Developed a special model for muSR spectra analysis under pressure.

Abstract

The pressure dependence of the magnetic penetration depth in polycrystalline samples of YBa2Cu3Ox with different oxygen concentrations x = 6.45, 6.6, 6.8, and 6.98 was studied by muon spin rotation (muSR). The pressure dependence of the superfluid density (p_s) as a function of the superconducting transition temperature Tc is found to deviate from the usual Uemura line. The ratio (dTc/dP)/(dp_s/dP) is factor of 2 smaller than that of the Uemura relation. In underdoped samples, the zero temperature superconducting gap and the BCS ratio both increase with increasing external hydrostatic pressure, implying an increase of the coupling strength with pressure. The relation between the pressure effect and the oxygen isotope effect on the magnetic penetration depth is also discussed. In order to analyze reliably the muSR spectra of samples with strong magnetic moments in a pressure cell, a special model was developed and applied.