The La <sub> 1.6-x </ Sub> Nd <sub> 0.4 </ Sub> Sr <sub> The X </ Sub> Of Cuo <sub> 4 </ Sub> Single Crystals Of The Transport Properties And Vortex Dynamics Research,

It has been proposed that the charge inhomogeneity is an intrinsic phenomenon to the doped antiferromagnets like cuprate superconductors. Evidences for charge stripe in a lot of high temperature superconductors have been given by neutron scattering experiments. In the model of stripe phase, the doped charges aggregate into stripes, and move in these "charge rivers" without disturbing the underlying antiferromagnetic CuO₂ planes. The stripe phase induces modulation of charge, spin and superconductivity in the CuO₂ planes, and plays an important role in the properties of high temperature superconductors.In this dissertation, the effect of stripe phase on superconductivity and anisotropy, the interaction between the stripe and the vortex and the vortex dynamics in static stripe system were studied systematically studied through resistivity study in La_1.6-xNd_0.4Sr_xCuO₄ single crystals under magnetic fields. The IV Characteristics of La_2-xSr_xCuO₄ based heterojunction and the effect of superconductivity on the IV Characteristics were also studied.This dissertation consists of five chapters. The arrangement of the chapters and the main contents in each chapter are presented as follows:In chapter 1, the progresses of the studies on the stripe phase in high temperature superconductors were reviewed. The picture and experimental evidences of the stripe phase were given. The relation between stripe and superconductivity and the effect of stripe on transport behavior of magnetic structure of cuprate superconductors were discussed.In chapter 2, the crystal growth method by optical floating-zone single crystal furnace was introduced, and the influence of growth atmosphere and temperature on the quality of the La_2-xSr_xCuO₄ and La_1.6-xxNd_0.4Sr_xCuO₄ single crystal was studied. It was found that atmosphere of air is beneficial to the stable growth of the crystals while raising temperature in a certain range is beneficial to the quality of the crystals. According to these findings, we improve the growth method and successfully grew high quality crystals of La_2-xSr_xCuO₄ and La_1.6-xNd_0.4Sr_xCuO₄.In chapter 3, the in-plane and out-of-plane resistivities of La_1.6-xNd_0.4Sr_xCuO₄ single crystals were studied under magnetic fields up to 8 T. It was found that the superconducting transition temperature (T_c^onset)in the out-of-plane resistivity is higher than that of the in-plane one. The study of the upper critical field shows that both the anisotropy parameter and in-plane coherence length increase with the enhancement of static stripe order.In chapter 4, the c-axis resistivity of LNSCO single crystals under the in-plane magnetic fields was studied. A fourfold symmetry is found in the c-axis magnetoresistance upon rotating the magnetic field within the ab-plane, which originates from the stripe phase induced anisotropic flux pinning. The magnitude of the anisotropy in magnetoresistance shows a strongly doping as well as field dependence. It implies that the anisotropy of the pinning effect of the stripe depends both on the superconductivity and the stripe structure. Our study gives an experimental evidence for the pinning of vortex by the stripe, and can be treated as evidence for the stripe model from resistivity measurement.In chapter 5, the IV characteristics of heterojunction composed of La_1.84Sr_0.16CuO₄ and 1.0 wt% Nb-doped SrTiO₃ were systematically studied. It was found that the superconducting transition of LSCO leads to significant changes in the IV characteristics of junction. The obvious deviation of diffusion voltage from its original track indicates the opening of the superconducting gap, andâ–³V_d as functions of temperature and magnetic filed show the same behaviors as the superconducting gap. This might give an easy and effective means to dip into the energy gap of LSCO.