Effect of fluctuations on vortex lattice structural transitions in superconductors - art. no. 177009

The rhombic-to-square transition field H-square(T) for cubic and tetragonal materials in fields along [001] is evaluated using the nonlocal London the ory with the account of thermal vortex fluctuations. Unlike extended Ginzbu rg-Landau models, our approach shows that the line H-square(T) and the uppe r critical field H-c2(T) do not cross due to strong fluctuations near H-c2( T) which suppress the square anisotropy induced by the nonlocality. In incr easing fields, fluctuations cause a reentrance of the rhombic vortex lattic e, in agreement with recent neutron scattering data on borocarbides.