Wei Si, Yao Yao, Xiaoyuan Hou, Chang-Qin Wu
By considering explicitly the contribution of carrier's spin in various incoherent charge transfer (CT) process, we propose a fundamental mechanism for magnetoresistance in organic semiconductors. It is proven that the disentanglement between the carrier's spin and the local environment, accompanying the incoherent CT, contributes a reduction factor to the intermolecular CT rate. The entanglement is altered by the applied magnetic field, which leads to the magnetoresistance. Based on a hyperfine interaction model, we show the CT rate exhibits a general feature of a Lorenzian-shape saturation at large fields, together with an ultrasmall-field component. Furthermore, the ultrasmall-field component is shown to be a result of the coherent motion of carrier's spin, while the saturation behavior survives the loss of coherence. The magnetic-field dependence, as well as the obtained isotope effect, are in satisfying agreement with the experimental results [T.D. Nguyen \textit{et al.}, Nature Materials \textbf{9}, 345 (2010)]. The mechanism also explains the diversity of magnetoresistance observed in various organic materials.
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http://arxiv.org/abs/1207.1152
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