Spin effects in quench dynamics of quantum dots and molecules

We study the quench dynamics of correlated quantum dots and molecules attached to spin-polarized leads. We focus on the strong coupling regime, where electron correlations can give rise to the Kondo effect. We study the situations in which the quench is performed either in the coupling to external electrodes or in the position of the orbital level. The time-evolution of expectation values of local occupation and magnetization indicates a destructive role of the proximity induced exchange field on the Kondo state. For single-level quantum dots this takes place out of the particle-hole symmetry point, while for molecules with larger spin detrimental effect of exchange field occurs in the whole Kondo regime. We also analyze the relevant time scales for the development of corresponding exchange fields and study their dependence on temperature, coupling strength and position of orbital level. The analysis is done with the aid of the time-dependent density-matrix numerical renormalization group method.