Wednesday, November 4, 2009

A definitive signature of incoherent transport

Following up on previous posts about the absence of energy bands and charge transport in dendrimers. For incoherent transport (equivalent to hopping or small polaron transport) the mobility and conductivity has an activated form where the activation energy is one quarter of the reorganisation energy associated with a charge moving off or on the relevant unit. But how can one distinguish such activated behaviour from what occurs in a regular semiconductor?

Also measure the temperature dependence of the thermopower. The associated energy scale will be much less than the activation energy of the mobility. This is seen nicely in the figure below taken from a review by Salamon and Jaime about colossal mangetoresistance materials.

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