The role of impact ionization in the transport properties of a periodically driven correlated layer - a Floquet DMFT study

Recently, Mott-insulating heterostructures have been proposed as candidates for highly efficient solar cells [1,2]. Here, photoexcited doublons and holes act as charge carriers which can proliferate due to impact ionisation processes [2]. Previous works have investigated the doublon dynamics in such systems within time-dependent Dynamical Mean-Field Theory (DMFT) by looking at the time evolution after a photoexcitation [3,4].

In the present work we focus on the (quasi-) steady state of periodically driven quantum systems. Specifically, we implement an algorithm to deal with periodic steady states of strongly correlated systems, making use of the nonequilibrium Floquet Green's function formalism within the DMFT approximation. Our model consists of a correlated layer subject to a periodic driving via a homogeneous electric field coupled to leads with an applied bias voltage. Furthermore, we generalize the system to a multilayer structure where the additional layers are used to model an electric field gradient.

We employ the Auxiliary Master Equation Approach (AMEA) [6-8] to solve the time averaged impurity problem and assess the validity of this approximation by comparison with Iterated Perturbation Theory (IPT) [9].

Investigating the results for the double accupancy, current and spectralfunction in dependence
of the external driving frequency suggests that impact ionization plays a domniant role in
the steady state dynamics.

References

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[2] E.Assman et al., Phys. Rev. Lett. 110, 078701 (2013)
[3] J.Coulter et al., Phys. Rev. B 90, 165142 (2014)
[4] M.Eckstein and P. Werner, Phys. Rev. Lett. 113, 076405 (2014)
[5] P. Werner et al., Phys. Rev. B 90, 235102 (2014)
[6] E. Arrigoni et al., Phys. Rrev. Lett. 110, 086403 (2013)
[7] I. Titvinidze et al., Phys. Rev. B 92, 245125 (2015)
[8] A.Dorda et al., New J. Phys., to be published (2017)
[9] A. Joura et al., Phys Rrev. B 91, 245153 (2015)