Front dynamics in the Harper model

The front dynamics in the Harper (or Aubry-André) model (which has a localization transition) is investigated using two different settings: the particle number front, where the system is at zero temperature and, initially, the particle numbers differ on the two sides, and the temperature front, where the two sides have different temperatures 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 the 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 time. The mutual information between neighboring intervals at the front has been calculated, and it is proportional to the logarithm of the interval length and also to the logarithm of 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 but differ for the finite-temperature front.