Vortex matter in superconductors

The behavior of the ensemble of vortices in the Shubnikov phase in biaxiall y oriented films of the high-temperature superconductor YBa2Cu3O7-delta (YB CO) in an applied magnetic field is investigated for different orientations of the field. The techniques used are the recording of the current-voltage characteristics in the transport current and of resonance curves and dampi ng of a mechanical oscillator during the passage of a transport current. It is shown that the behavior of the vortex ensemble in YBCO films, unlike th e case of single crystals, is determined by the interaction of the vortices with linear defects-edge dislocations, which are formed during the pseudom orphic epitaxial growth and are the dominant type of defect of the crystal lattice, with a density reaching 10(15) lines/m(2). The effective pinning o f the vortices and the high critical current density (J(c)greater than or e qual to 3x10(10) A/m(2) at 77 K) in YBCO films are due precisely to the hig h density of linear defects. New phase states of the vortex matter in YBCO films are found and are investigated in quasistatics and dynamics; they are due to the interaction of the vortices with crystal defects, to the onset of various types of disordering of the vortex lattice, and to the complex d epinning process. A proposed H-T phase diagram of the vortex matter for YBC O films is proposed. (C) 2001 American Institute of Physics.