Vortex matter in superconductors

The behavior of the ensemble of vortices in the Shubnikov phase in biaxially oriented films of the high-temperature superconductor YBa2Cu3O7−δ(YBCO) 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 damping of a mechanical oscillator during the passage of a transport current. It is shown that the behavior of the vortex ensemble in YBCOfilms, unlike the case of single crystals, is determined by the interaction of the vortices with linear defects—edge dislocations, which are formed during the pseudomorphic epitaxialgrowth and are the dominant type of defect of the crystal lattice, with a density reaching 1015 lines/m2. The effective pinning of the vortices and the high critical current density (Jc⩾3×1010 A/m2 at 77 K) in YBCOfilms are due precisely to the high density of linear defects. New phase states of the vortex matter in YBCOfilms 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 depinning process. A proposed H–T phase diagram of the vortex matter for YBCOfilms is proposed.