Neutron diffraction from the vortex lattice in the heavy fermion superconductor UPt3 (invited) (abstract)

The heavy fermion superconductor UPt3 is thought to have a d-wave pairing ground state. The principal experimental evidence for this consists of the anisotropy of the power-law behavior observed in transverse ultrasound and μ+ SR measurements. The observation of a complex phase diagram in the superconducting state in ultrasound, torsional oscillator, and specific heat measurements may be a further indication of an unconventional pairing state. Theoretical investigations suggest the possibility of vortex lattices that are unconventional in their symmetry, their quantization, or the structure of their composite vortex cores. Transitions between such exotic vortex lattices are in principle allowed and could explain the observed features at H≊0.6 Hc2 (for H∥ĉ) and H≊0.3Hc2 (for H⊥ĉ). Neutron diffraction is an ideal bulk probe of the microscopic properties of the vortex lattice. We have studied the vortex lattice with H⊥ĉ and T≊50 mK in the field range 0.75