Neutron scattering from the flux-line lattice in Bi₂Sr₂CaCu₂O_8+#gamma#

Neutron small-angle diffraction has been used to investigate the flux-line lattice structure within single crystals of the high-temperature superconductor Bi2.15Sr1.95CaCu2O8+x. The diffracted intensity goes rapidly to zero as the magnetic field or the temperature is increased. Melting at low fields as a function of temperature coincides with the appearence of finite resistance within the superconducting state. At low temperatures the diffracted intensity disappears in fields greater than similar to 70 mT, probably due to the decomposition of the flux-line lattice into randomly pinned 2d ''pancake'' vortices.