| High-temperature superconductors are strongly correlated electronic materials, in which spin, charge, lattice are simultaneously active. Many experimental results have provided evidences for the existence of nanometer-scale electronic inhomogeneity in high-Tc cuprates. The charge stripes are one of the highly debating topics. In the CuO2 plane, doped holes accommodate in striped pattern and separate the antiferromagnetic domains, forming a long-range modulation. The fluctuation of charge stripes as well as spin stripes are the key elements to the high-Tc superconductivity.In this dissertation, the transport properties as well as current-voltage (Ⅳ) characteristics in magnetic fields of strained La1.44Nd0.4Sr0.16CuO4 films deposited on LaSrAl04 substrates were studied. The relation between stripe order and superconductivity and the effect of stripe order on the vortex phase transition are discussed. Moreover, the effect of in-plane impurity substitution on the local structural transformation in La1.88Sr0.12Cu1-yZyO4 was investigated by ultrasonic measurement and evidence for electron-lattice coupling in this system was found.In chapter one, anomalous phenomena related to charge inhomogeneity in high-Tc cuprates revealed by different experimental methods are introduced. The concept of charge stripe phase as well as its relation to high-Tc superconductivity is introduced. The vortex structure and flux pinning in the stripe-ordered superconducting state are also discussed.In chapter two, the preparation of high quality La1.6-xNd0.4SrxCuO4 (LNSCO) and La1.88Ba0.12CuO4 (LBCO) epitaxial films and photolithography method are introduced. The zero-field transport properties of LNSCO and LBCO films of different thickness were studied and the effect of in-plane compressive strain on the structure and the superconducting transition temperature Tc was discussed. The c-axis expansion and destabilization of static charge stripes are possibly responsible for the promotion of Tc.In chapter three, the in-plane resistivities of La1.44Nd0.4Sr0.16CuO4/LaSrAlO4 films were studied in magnetic fields. A crossover from parallel shift to fan-shape broadening in the resistivity transitions was observed as in-plane compressive strain increased. Moreover, the upper critical field, in-plane coherence length and the effective pinning potential of the films were also found to change with increasing in-plane compressive strain and which is closely related to the increase of superconductivity induced by the strain.In chapter four, the IV characteristics of two La1.44Nd0.4Sr0.16CuO4/ LaSrAlO4 films with different strained state are presented. We provide clear evidences that in a superconducting state with dynamical stripe order, a typical 3D VG phase transition is found. While in a stripe-ordered superconducting state, the vortex phase transition bears 2D characteristics. Moreover, for the sample with static stripe order, we find that the correlation length used for scaling in the vortex liquid state is of KT-type, in which anti-vortex pairs dominate. Below the VG phase transition temperature Tg, the VG correlation length should be used in order to achieve good scaling collapse, indicating a quasi-2D vortex glass phase. Our findings indicate that the nature of vortex phase-transition is completely altered in the presence of the stripe order.In chapter five, the effect of in-plane substitution on the local structure has been studied by ultrasonic method in a series sample of La1.88Sr0.12Cu1-yZnyO4(y=0.00,0.01, 0.02, 0.03). It is found that a small amount of Zn doping greatly promotes the formation of local low-temperature tetragonal (LTT) phase, whereas further doping is harmful to it, whose tendency shows a marked resemblance to the Zn-concentration dependence of magnetic transition temperature TN reported byμSR study. This result indicates that the spin, charge and lattice are simultaneously active in this system. Our results also provide additional evidence that the slight in-plane nonmagnetic doping introduces local pinning centers to stabilize the charge stripes in La1.88Sr0.12CuO4.
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