Overend, Howson, and Lawrie Reply:

Search for spontaneous nucleation of magnetic flux during rapid cooling ofYBa2Cu3OCarmi1, Polturak2 1999Phys. Rev. B621830View full textAdd to dashboardCite

“…Because the phase transition in YBCO is not a pure Ginzburg-Landau type, closer to the 3D-XY model, the value of the exponent p is deduced from experiments that measured the exponents ν and µ [15][16][17][18]. We chose average values: ν ≃ 0.67, µ ≃ 3.4 (note that this is an unusual scaling), and then p ≃ 0.3.…”

3D-XY Critical Fluctuations of the Thermal Expansivity in Detwinned YBa2Cu3O7-δ Single Crystals Near Optimal Doping

“…For example, in specific heat measurements of YBa 2 Cu 3 O 7-δ the fluctuation component is at most 5 % of the large phonon background. By slightly adjusting the unknown phonon background, both critical and 3D-Gaussian type models can be fitted quite well [1,3,[4][5][6]. The fitting residuals of the most recent specific heat measurements are somewhat smaller for the critical than for the Gaussian fits [3,4,6,14], although quite different backgrounds, with and without mean-field contributions, were used for the critical analyses.…”

“…In contrast, the small coherence lengths, high transition temperatures and quasi-2D nature of high-temperature superconductors (HTSC) greatly enlarge the temperature region in which fluctuations of the order parameter are important, and fluctuations in HTSCs have been observed in many types of experiments, e.g. specific heat [1][2][3][4][5][6], thermal expansion [7,8], resistivity [2,9], penetration depth [10,11] and magnetization [3,6,12] measurements. A large effort has gone into quantifying these effects, because a detailed analysis of the fluctuations can provide important information regarding the dimensionality and the order parameter of the superconducting state.…”

“…Penetration depth measurements, which are ideally not plagued by any background, on YBa 2 Cu 3 O 7-δ appear to yield both critical [10] and mean-field type exponents [11,15]. Thus, although there is increasing evidence for critical behavior in YBa 2 Cu 3 O 7-δ [4,6,9,10], the width of the critical region and the exact values of the critical exponents remain uncertain, and further experiments are desirable.…”

Universal scaling properties of superconductors in magnetic fields

“…On a more pragmatic note, experimentally there is now ample evidence [5][6][7] that for high-T c superconductors, for |T − T c | ≤ 10K, the zero field transition exhibits critical behaviour characteristic of a three dimensional XY -model. This fact, together with the finite size analogy, has been utilized [8] to collapse experimental specific heat data using a "finite size" scaling ansatz of the form P = τ θ X( B Φ0 τ −2ν ), where τ is a linear deviation from the critical temperature and ν and θ are XY exponents, with ν ∼ 0.67 for a three dimensional sample.…”