Pinning and Dynamics of Pseudospin Condensates in Practical Crystals

Abstract

In the critical region pseudospin condensates are in such a sinusoidal form as σ ₀ cos φ and σ ₀ sin φ, where φ = qx − ϖt + φ ₀, propagating through the lattice at a speed υ = ϖ/q. In an idealized “perfect crystal” the phase constant φ ₀ is undetermined, unless a boundary condition is imposed on the phase φ at certain space—time coordinates (x ₀, t ₀) in the lattice. It is realized that small values of q and ϖ as determined from light and neutron inelastic scattering experiments do not constitute evidence for the condensate as a moving object through the lattice. To substantiate its presence in practical crystals, the condensate must be directly sampled by using, for instance, magnetic resonance probes substituted for constituent ions in the active groups. Even so, a propagating condensate could not be properly sampled in the laboratory frame of reference, unless the observer is moving at the same speed υ as the object.