Evolution of the excess conductivity in slightly doped YBa2Cu3O7-δ under high pressure

Abstract

The influence of hydrostatic pressure up to P=1.05 GPa on resistivity, excess conductivity σ/(T) and pseudogap (PG) Δ*(T) in slightly doped single crystals of YBa2Cu3O7-δ (Tc(P = 0) ≈49.2 K and δ ≈ 0.5) is studied. For the first time it is found that the BCS ratio 2Δ*/kBTc and PG Δ* both increase with increasing external hydrostatic pressure at a rate dlnΔ*/dP ≈ 0.37 GPa-1, implying an increase of the coupling strength with pressure. Simultaneously, the critical temperature Tc also increases with increasing pressure at a rate
dTc/dP = +5.1 K·GPa-1, whereas resistivity ρ(300K) decreases at a rate dlnρ/dP = (-19±0.2)% GPa-1. Independently on pressure near Tc σ/(T) is well described by the Aslamasov-Larkin and Hikami-Larkin fluctuation theories demonstrating 3D-2D crossover with increase of temperature. The crossover temperature T0 determines the coherence length along the c-axis ξc(0) = (3.43 ± 0.01)Ǻ at P=0 GPa, which decreases with pressure.