Peak effects and the solid vortex phase of aT*-phaseSmLa0.8

Abstract

The isothermal magnetization curves obtained from a superconducting T*-phase SmLa 0.8 Sr 0.2 CuO 4Ϫ␦ single crystal have demonstrated the existence of distinct peak effect in a large temperature range, persisting up to the vicinity of the superconducting critical temperature (T c on Ϸ24 K͒. The magnetization curves also exhibit the remarkable feature of zero-field peaking and its enhancement at lower temperature. Analysis of the associated vortex phase diagram further establishes the role of geometrical barrier in the retardation of vortex penetration at high temperature and that of surface barrier at lower temperature. The temperature dependence of the second peak field is also found to conform with existing models at the appropriate temperature regimes. Additionally, the irreversibility line shows a sign reversal of its slope at a field position around H 2D indicating twodimensional melting at higher field. Nevertheless, the temperature dependent behavior of the second peak onset field is at variance with other published results and defies explanation on the basis of existing theoretical models.

Doping dependence of the vortex glass and sublimation transitions in the high-Tc superconductor La2-xSrxCuO4 as determined from macroscopic measurements

“…Our observations show that equation 3holds over a very large doping range in LSCO, and strongly support the sublimation scenario. It remains to discuss the second peak line H sp (T ) which has been explained on the basis of the thermal decoupling theory [45][46][47], which predicts the suppression of long-range order in the direction of the applied field due to thermal fluctuations. The expected temperature dependence is [46]…”

“…γ is the only free parameter, and the fitted values are in good agreement with the measured values of the anisotropy (see Table I). It remains to discuss the second peak line H sp (T ) which has been explained on the basis of the thermal decoupling theory 45,46,47 , which predicts the suppression of 6 , of the penetration depth λ ab 37 , and of the anisotropy γ 2,38,44 have been extrapolated from experimental values found in the literature. Hm and m have been obtained by fitting the data by Eq.…”

Intrinsic parameters of aT*-phaseSmLa0.8Sutjahja1, Nugroho2, Tjia3 et al. 2002Phys. Rev. BSelf Cite

“…2 Combined with the in-plane parameters in the Table I, this ␥ value leads to an estimated c-axis coherence length of c (0)Ϸ1.17 Å for our sample. Compared to the large effective interlayer distance sϷ15.50 Å, 5 this value of c (0) clearly signifies a weak interlayer Josephson coupling in the system, which leads in turn to the relatively large thermal fluctuation effect at temperatures approaching T c .…”