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Dielectric breakdown of Mott insulators -- doublon production and doublon heating

Using dynamical mean-field theory and the non-crossing approximation as impurity solver, we study the response of a Mott insulator to strong dc electric fields. The breakdown of the Mott insulating state is triggered by field-induced creation of doublon-hole pairs. In a previous investigation, Ref. [1], it was found that the system approaches a long-lived quasi-steady state in which the current is time-independent although the number of carriers constantly increases. Here we investigate and clarify the nature of this state, which exists only because thermalization is slow in the Hubbard model at strong coupling. The current is time-independent because doublons and holes have an infinite temperature distribution. Evidence for this fact is obtained from spectral functions and by comparing the electric current with the field-induced doublon-hole creation rate. Implications to real experiments, in systems with energy dissipation, are discussed.