C.E. Sosolik, Joseph A. Stroscio, M.D. Stiles, E.W. Hudson, S.R. Blankenship, A.P.ÿFein, and R.J. Celotta
Electron Physics Group, National Institute of Standards and Technology, Gaithersburg, MD 20899-8412

Measurements of the structural evolution of the vortex lattice in a single-crystal V3Si sample have been performed using low temperature scanning tunneling microscopy. Large-scale conductance maps obtained at 2.3 K provide a real-space image of the vortex lattice formed with a magnetic field applied parallel to the [001] crystal axis. Atomic resolution topography of the V3Si (001) surface shows the underlying Si sublattice and allows for a determination of the orientation of the measured vortex lattice relative to the underlying crystal axes. The conductance maps reveal a shift in the symmetry of the vortex lattice from hexagonal to nearly square over the field range of 0 T to 4 T. Near 4 T, a strong anisotropy in the long-range translational order of the vortex lattice is observed, with the lattice preferentially shearing along one of the [110] directions. These observations give evidence for nonlocal electrodynamics in the vortex-vortex interactions of this Type II superconductor. Calculations that account for the role of these nonlocal effects in determining the structure and symmetry of the vortex lattice are presented and compared to our experimental results.