Front dynamics in the Harper model

Abstract

The front dynamics in the Harper (or Aubry-Andr\'e) model (which has a localization transition) is investigated using two different settings, particle number front where the system is at zero temperature, and initially, the particle numbers differ on the two sides, and temperature front where the two sides have different temperature initially. The two differently prepared half systems are connected suddenly, and the following dynamics is investigated. In the extended phase, the dynamics is ballistic, similar to the dynamics of a pure system. At the critical point, one finds a power-law time dependence of the particle number and the entanglement entropy of the zero temperature setting. In the localized phases, the observables oscillate around an average value, which is independent of the system size. The particle number front shapes have been investigated at zero temperature setting, in the extended phase they scale together exactly as in the homogeneous XX chain, however at the critical point the scaling relation contains a power ($t^{0.55}$) of the time. The mutual information between neighboring intervals at the front has been calculated, and it is promotional with the logarithm of the interval length and also with the logarithm of the time in the extended phase and at the critical point. The prefactors of the time and size dependence are equal for the zero temperature process, however differ for the finite temperature front.