Static and Dynamic Properties of the Vortices in Single Crystalline CeRu_2

Abstract

Elastic constants of CeRu₂ have been measured as functions of temperature and magnetic field. The tilt elastic strain couples strongly with the vortices. The elastic anomaly Δ c due to the vortices is well described by the formula Δ c=(B²/4π)cos²θ/(1+λ²k²), where θ is the angle between the propagation of the transverse sound with the wave number k and the magnetic flux density B. By using this formula, we got the number of the pinned vortices and the coefficient λ as functions of temperature and magnetic field. The vortex state can be classified into three regions with respect of the fraction of the pinned vortices; flux-flow, strong pinning and weak pinning. The strong vortex pinning is associated with the tetragonal deformation of the lattice in the magnetic field caused by the soft (c₁₁-c₁₂)/2 of CeRu₂, which is due to high density of states in the Brillouin zone.