Abstract
We study the dynamics of large polarons in diatomic molecular chains, at zerotemperature, under the influence of an external, periodic in time, electric field of zero meanvalue. We show that in asymmetric chains, i.e. chains with two different atoms per unit cell,a harmonic unbiased field causes a drift of such polarons. Such a drift current, known asthe ratchet phenomenon, depends strongly on the parameters of the chain; in particular, onthe extent of the anisotropy of the chain and on the size of the polaron. Moreover, thedrift takes place only if the intensity and the period of the field exceed somecritical values which also depend on the parameters of the chain. We show thatthis directed current of polarons is a complicated phenomenon. It takes placein dissipative systems with a broken spatial symmetry and is generated by theinterplay between the Peierls–Nabarro barrier and the impact of the externalfield on the charged polarons. The dependence of the amplitude of the polaronoscillations, the size of the drift per period of the external field and the average velocityare determined as a function of the intensity of the field and of its frequency.
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