RESUMO
The noncentrosymmetric superconductor Ru7B3has in previous studies demonstrated remarkably unusual behaviour in its vortex lattice (VL), where the nearest neighbour directions of the vortices dissociate from the crystal lattice and instead show a complex field-history dependence, and the VL rotates as the field is changed. In this study, we look at the VL form factor of Ru7B3during this field-history dependence, to check for deviations from established models, such as the London model. We find that the data is well described by the anisotropic London model, which is in accordance with theoretical predictions that the alterations to the structure of the vortices due to broken inversion symmetry should be small. From this, we also extract values for the penetration depth and coherence length.
RESUMO
Thermal expansion measurements have been performed on single crystals of R2-2xSr1+2xMn2O7 (R=Pr, Nd, and Dy) over a wide temperature range (4-900 K). Our analysis allows us to give a general explanation for the large lattice anomalies observed in the layered manganites. Localization of the carriers gives rise to volume and anisotropic anomalies in the paramagnetic regime. The anisotropic distortion is enhanced with the establishment of long-range antiferromagnetism, whereas it is quenched by long-range ferromagnetic order.