Persistent Tunneling Currents and Magnetic-Field Effects in Glasses

Recent experiments on insulating glasses showed an unexpected variation of the dielectric constant with a static magnetic field and, in particular, oscillations with an apparent flux quantum of about 10^-5h/e. We propose an explanation for these phenomena in terms of a model based on pairs of two-level systems. A weak interaction is shown to give rise to quantum states with a net circular current and a linear field dependence of the energy levels. Under experimental conditions, the dynamic susceptibility shows oscillatory behavior, with an effective flux quantum of the order of 10^-5h/e.