THEORY OF NEUTRON-DIFFRACTION FROM THE VORTEX LATTICE IN UPT3

Neutron scattering experiments have recently been performed in the sup erconducting state of UPt3 to determine the structure of the vortex la ttice. The data show anomalous field dependence of the aspect ratio of the unit cell in the B phase. There is apparently also a change in th e effective coherence length on the transition from the B to the C pha ses. Such observations are not consistent with conventional supercondu ctivity. A theory of these results is constructed based on a picture o f two-component superconductivity for UPt,. In this way, these unusual observations can be understood. There is a possible discrepancy betwe en theory and experiment in the detailed field dependence of the aspec t ratio.