Fluctuation specific heat in multilayered superconductors: Bilayered Gaussian-Ginzburg-Landau scenario for the thermal fluctuations of Cooper pairs around Tc in YBa2Cu3O7−δ single crystals

Abstract

The effects around the superconducting transition of thermal fluctuations of Cooper pairs on the heat capacity in zero applied magnetic field (H=0) are explicitly calculated in bilayered superconductors, with two superconducting layers and tunneling couplings per layer periodicity length. The calculations are performed on the grounds of a generalization to multilayered superconductors of the Lawrence-Doniach Ginzburg-Landau functional, and assuming Gaussian fluctuations. In addition to the fluctuation heat capacity cfl, we also obtain various useful relationships between cfl and other fluctuation-induced observables experimentally accessible in multilayered copper oxide superconductors. It is then shown that if the effects of the multilaminarity are taken into account, the mean-field-like Gaussian-Ginzburg-Landau approach may explain simultaneously and at a quantitative level the available experimental data, both the amplitude and the ε behavior, of the fluctuation specific heat, the in-plane paraconductivity Δσab, and the fluctuation-induced diamagnetism Δχab, in YBa2Cu3O7−δ(Y−123) single crystals under zero or weak magnetic fields (H→0), up to reduced temperatures of the order of ε≡|T−Tc|/Tc∼10−2. The corresponding coherence length amplitudes (at T=0K) are ξab(0)=1.1nm and ξc(0)=0.12nm for the in-plane (ab) and transversal (c) directions, respectively. In contrast, the same data cannot be explained, in the same ε region, in terms of the 3DXY theory for full-critical fluctuations with a value of the dynamic critical exponent of z=32, which corresponds to the same universality class as the superfluid-normal λ transition of 4He liquid, although these analyses do not exclude the applicability of such a scenario for ε≲10−2, as suggested by previous measurements of Δσab and Δχab in the same Y-123 single crystals. However, another dynamic universality class, with z=2, makes the 3DXY full-critical behavior compatible with the experimental data for 2×10−2≲ε≲10−1.

Source-reported materials — not catalogue approval

Similar papers