Universality of frequency and field scaling of the conductivity measured by ac susceptibility of aYBa2Cu3

Abstract

Utilizing a novel and exact inversion scheme, we determine the complex linear conductivity σ(ω) from the linear magnetic ac-susceptibility which has been measured from 3 mHz to 50 MHz in fields between 0.4 T and 4 T applied parallel to the c-axis of a 250 nm thin disk. The frequency derivative of the phase σ ′′ /σ ′ and the dynamical scaling of σ(ω) above and below Tg(B) provide clear evidence for a continuous phase transition at Tg to a generic superconducting state. Based on the vortexglass scaling model, the resulting critical exponents ν and z are close to those frequently obtained on films by other means and associated with an 'isotropic' vortex glass. The field effect on σ(ω) can be related to the increase of the glass coherence length, ξg ∼ B.

Percolative vortex motion in high-temperature superconductors

“…16 A semiquantitative agreement was found for ac susceptibility measurements on Bi 2 Sr 2 CaCu 2 O 8 single crystals 17 and for vibrating reed measurements on YBa 2 Cu 3 O 7Ϫ␦ single crystals and films. 18 Reed et al 8 and Kötzler et al 9,10 showed that the extended TAFF model was in quantitative agreement with the frequency-dependent ac susceptibility of Y-1:2:3 single crystals and films near T c , whereas the ac susceptibility at lower temperatures was in agreement with the existence of critical fluctuations around a vortex glass transition temperature T g .…”

“…The ratio of the critical exponents observed in YBa 2 Cu 3 O 7Ϫ␦ films, 35,10,37 t/sϭ4.4Ϯ0.7, is considerably higher than the theoretical value, indicating the presence of a continuous distribution of bond diffusivities.…”

“…In Table I 35 Kötzler et al, 10 and Baselgia Stahel et al 37 found values zϾ5 for Y-1:2:3 films. These values are in agreement with critical exponents obtained from the scaling of the nonlinear dc resistivity.…”

“…͑23͒ 10 from the numerical inversion of the frequency-dependent ac susceptibility. The phase angle ⌽(T g )ϭ0.82( /2) at the transition temperature T g ϭ88.9 K is independent of frequency in agreement with the scaling law, Eq.…”

“…3,4 Near the transition between the glassy and the liquid vortex phases the electronic conductivity obeys scaling laws 1,2 and far above the transition the motion of the vortex liquid is diffusive. [5][6][7] The existence of a scaling regime for the linear, frequency-dependent conductivity [8][9][10] ( ) and the nonlinear dc conductivity 11,12 ( j) is firmly established. Though these experimental findings in transport quantities support the existence of a vortex glass transition, measurements of thermodynamic variables have not shown an indication of a phase transition.…”