Anisotropy in spatial order-disorder transformations and the vortex lattice symmetry transition in YNi2B2C and LuNi2B2CD. Jaiswal-Nagar1, 2, 3, T. Isshiki1, N. Kimura1, H. Aoki1, H. Takeya4, S. Ramakrishnan2 and A. K. Grover2
1 Centre for Low Temperature Science, Tohoku University - Sendai, Miyagi, 980-8578, Japan
2 DCMP&MS, Tata Institute of Fundamental Research - Mumbai-400005, India
3 Physikalishes Institut, Goethe-Universität - 60438 Frankfurt am Main, Germany
4 National Institute for Materials Science - Sengen 1-2-1, Tsukuba, Ibaraki 305-0047, Japan
received 18 August 2008; accepted in final form 13 November 2008; published December 2008
published online 12 January 2009
Explorations of the order-disorder transformation in vortex matter in single crystals of tetragonal structured (c/a ~ 3) borocarbide superconductors, YNi2B2C and LuNi2B2C, reveal that vortex arrays experience different effective pinning in different crystallographic directions. We surmise that correlation exists between the large anisotropy in effective pinning/disorder and the differences in the (local) symmetry transition from rhombohedral to (quasi)square vortex lattice (VL). For a field along high-symmetry directions, like, the c-axis and ab basal plane, the VL symmetry is close to square and the ordered state spans a large field interval. When the field is turned away from the c-axis towards the ab-plane, at intermediate angles, the region of the ordered state shrinks, in response to enhancement in effective pinning. At such intermediate angles the symmetry of the VL would be far from ideal triangular or square.
74.25.Dw - Superconductivity phase diagrams.
74.25.Qt - Vortex lattices, flux pinning, flux creep.
74.70.Dd - Ternary, quaternary, and multinary compounds (including Chevrel phases, borocarbides, etc.).
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