Neutron diffraction from the vortex lattice in the heavy fermion superconductor UPt3 (invited) (abstract)
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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<H<10 kG. The structure of the vortex lattice and the quantization of the vortices, in addition to the London penetration depth, λL, the coherence length, ξ, and the effective mass anisotropy are all well determined by our measurements. The lattice is oblique hexagonal with conventional quantization. Its anisotropy can be explained by considering a combination of Fermi surface and gap anisotropy. However, the lattice does not appear to change near the transition between superconducting phases identified by other techniques.
