Search

The detailed flux line lattice (FLL) structure in YNi2B2C was investigated using small angle neutron scattering and the complete H‐T phase diagram was determined. The FLL in YNi2B2C shows a change of symmetry only in the low magnetic field region between 0.05 to 0.2 T. The observed square lattice is governed by an anisotropic Fermi velocity. Contrary to the theoretical prediction, a square lattice driven by an anisotropic superconducting gap does not appear below 5 T.

Recently Nakai et al. reported a theoretical H – T phase diagram of flux line lattice (FLL) structure in which successive transitions from a triangular, a square (\(\square_{\text{v}}\)), a triangular and another square (\(\square_{\text{g}}\)) occur with increasing a magnetic field. Here \(\square_{\text{v}}\) and \(\square_{\text{g}}\) indicate the FLL structures reflecting anisotropies in the Fermi velocity and the superconducting gap, respectively. In the case of YNi 2 B 2 C, \(\square_{\text{v}}\) and \(\square_{\text{g}}\) should rotate by 45°. The low field transition from triangular to \(\square_{\text{v}}\) is observed in RE Ni 2 B 2 C ( RE =Er, Tm, Lu, and Y). However, there is no experimental evidence for the appearance of \(\square_{\text{g}}\) phase so far. We studied the FLL structure of YNi 2 B 2 C in the higher field region by small-angle neutron scattering. Our results show that a large area of the H – T phase diagram is occupied by \(\square_{\text{v}}\) phase and there is no evidence fo...