Neutron diffraction from the vortex lattice in the heavy-fermion superconductor UPt3.

Abstract

We have used neutron diffraction to observe the vortex lattice of ${\mathrm{UPt}}_{3}$. This is the first such measurement in a heavy-fermion system, a superconductor below 1 K, or in a system with such a long magnetic penetration depth (6000\ifmmode\pm\else\textpm\fi{}75 \AA{}). It also provides the first value for the pair coherence length, 111\ifmmode\pm\else\textpm\fi{}2\AA{}, to be obtained directly within the pairing state of ${\mathrm{UPt}}_{3}$. The lattice is oblique hexagonal with conventional quantization. Its anisotropy can be explained by considering a combination of gap and Fermi-surface anisotropies. The lattice does not appear to change near the transitions between the superconducting phases identified by other techniques.