Vibrations of a magnet levitated over a flat superconductor

Based on a dipole-dipole interaction model, we discuss the levitation force and related vibration problems to understand the effects of flux pinning in type-II superconductors, and the applications of levitation in superconducting systems.     

Emergence of classicality for primordial fluctuations: Concepts and analogies

We clarify the way in which cosmological perturbations of quantum origin, produced during inflation, assume classical properties. Two features play an important role in this process: First, the dynamics of fluctuations which are presently on large cosmological scales leads to a very peculiar state (highly squeezed) that is indistinguishable, in a precise sense, from a classical stochastic process. This holds for almost all initial quantum states. Second, the process of decoherence by interaction with the environment distinguishes the field amplitude basis as the robust pointer basis. We discuss in detail the interplay between these features and use simple analogies such as the free quantum particle to illustrate the main conceptual issues.     

The effect of buoyancy on the weight gain signal in LEC crystal growth

Crystal diameter monitoring in liquid encapsulated Czochralski (LEC) growth using the weighing method is investigated. An analytical expression for the differential weight gain signal is derived for stationary growth conditions accounting for bouyancy. For the GaAs/B₂O₃ system the buoyancy component of the signal can easily amount to 30%. The formula can be applied to determine the crystal/melt interface area, provided the radius of the part emerging from the encapsulant is known, either in advance as the seed dimension, or by separate monitoring using, e.g., conventional optical methods.