Mechanical Measurements of the Flux Lattice in the Heavy-Fermion Superconductor UPt3

We report mechanical measurements of the flux lattice in UPt3. In the superconducting state the flux lattice that is formed in the sample when a magnetic field is applied contributes a restoring force and a dissipation term to a high-Q mechanical oscillator, when the oscillator and sample are tilted with respect to the static magnetic field. In addition to the characteristic response for a type-II superconductor that gives Hc2(T), we observe an …