The effect of in-plane mass anisotropy on the properties of high temperaturesuperconductors in states of mixed symmetry

Abstract

Experiments have suggested that the high-Tc cuprate YBCO shows marked anisotropy in penetration depth and coherence lengthmeasurements. In order to take into account the presence of this anisotropy inthe system and its corresponding effect on the various properties of the high-Tc superconducting materials, we have developed an anisotropic two-orderparameter Ginzburg–Landau (GL) theory involving a mixed symmetrystate of the order parameter components. For this we have generalized atwo-order parameter GL theory, recently developed for the isotropic high-Tc superconductors involving a mixed symmetry state of the order parameter components(Karmakar and Dey 2008 J. Phys. Condens. Matter 20 255218), in which the effect ofthe presence of in-plane anisotropy has been taken into account by an effectivemass approximation, with the anisotropy being characterized by the parameterγ = mx/my. The work goes beyond the limitations of the earlier studies in this field as it enables us tocarry out a detailed study of the various properties of the system over the entire range ofapplied magnetic field and wide range of temperature for arbitrary values of the GL parameterκy and vortex lattice symmetry. The model successfully explains not only the observed obliquevortex lattice structure in the presence of in-plane anisotropy but also the experimentallyobserved angle between the primitive axes of the vortex lattice. The generation oftwo-fold symmetry of the vortices in the presence of in-plane anisotropy, for avery low applied magnetic field can also be analyzed by our model. We havealso compared our theoretical results with various other experiments on high-Tc cuprate YBCO.