Crossover from a three-dimensional to purely two-dimensional vortex-glass transition in deoxygenatedYBa2Cu3

Z. Sefrioui

¹

,

D. Arias

²

,

M. Varela

³

et al.

Abstract

Current-voltage (I-V) characteristics were used to investigate the response of the vortex-glass ͑VG͒ phase transition in high-quality epitaxial YBa 2 Cu 3 O 7Ϫ␦ films in magnetic fields up to 7 T. We show that varying the oxygen content, the scaling analysis reveals a crossover from three-dimensional ͑3D͒ to a pure 2D VG transition with T g ϭ0. At small oxygen deficiencies (7Ϫ␦ϭ6.75), the -j curves scale according to the 3D VG model, which cannot be distinguished from a Bose-glass model from a scaling analysis with the magnetic field applied parallel to the c axis. At a lower oxygen content (7Ϫ␦ϭ6.48), the VG phase transition behaves analogous to the highly anisotropic Bi 2 Sr 2 CaCu 2 O 8 samples, showing a quasi-2D VG transition. For further deoxygenated samples (7Ϫ␦ϭ6.4), the result is consistent with a pure 2D vortex-glass model similar to that observed in the even more anisotropic Tl 2 Ba 2 CaCu 2 O 8 thin films. The estimated value of the anisotropy in high-quality oxygen-depleted samples is comparable to that of the highly anisotropic superconductors.

Vortex-glass transitions in low-Tcsuperconducting Nb thin films andNb∕Cusuperlattices

“…4 Moreover, we want to underline that the obtained values are very similar to that observed for quasi -2D VG transitions in HTCS. 16,17 For instance, the same values of the critical exponents were found in YBa 2 Cu 3 O 7−δ thin films. 17 This fact stresses the universality of the VG transition, earlier suggested.…”

“…16,17 For instance, the same values of the critical exponents were found in YBa 2 Cu 3 O 7−δ thin films. 17 This fact stresses the universality of the VG transition, earlier suggested. 17,18 Recently, Strachan et al 11 have proved that the scaling method used is misleading, even in the case of universal critical exponents with adequate values were found.…”

“…17 This fact stresses the universality of the VG transition, earlier suggested. 17,18 Recently, Strachan et al 11 have proved that the scaling method used is misleading, even in the case of universal critical exponents with adequate values were found. They have argued that experimental limitations related to voltage sensitivity floor might allow achieving good collapses with arbitrary values of some of the scaling parameters, as for instance T g .…”

“…These are very high values of the critical exponents, not supported by theory. 4 As argued earlier, 16,17 this strongly suggests that a quasi -2D or 3D…”

“…However, a good scaling of the isotherms is achieved by assuming a different pure 2D VG transition, as first proposed by Dekker et al 19 , and later found in HTSC systems. 16,17 In a pure 2D VG transition, the glass transition temperature T g =0. Therefore a pure 2D VG phase does not exist at any finite temperature, although in-plane correlations (2D) develop, diverging as ξ V G ∝ 1 T ν ′ when temperature approaches…”