Bobbert P A, Nguyen T D, van Oost F W A, Koopmans B, Wohlgenannt M
Group Polymer Physics and Eindhoven Polymer Laboratories, Technische Universiteit Eindhoven, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
Phys Rev Lett. 2007 Nov 23;99(21):216801. doi: 10.1103/PhysRevLett.99.216801. Epub 2007 Nov 20.
We present a mechanism for the recently discovered magnetoresistance in disordered pi-conjugated materials, based on hopping of polarons and bipolaron formation, in the presence of the random hyperfine fields of the hydrogen nuclei and an external magnetic field. Within a simple model we describe the magnetic field dependence of the bipolaron density. Monte Carlo simulations including on-site and longer-range Coulomb repulsion show how this leads to positive and negative magnetoresistance. Depending on the branching ratio between bipolaron formation or dissociation and hopping rates, two different line shapes in excellent agreement with experiment are obtained.
我们提出了一种机制，用于解释最近在无序π共轭材料中发现的磁阻现象，该机制基于极化子的跳跃和双极化子的形成，同时存在氢原子核的随机超精细场和外部磁场。在一个简单模型中，我们描述了双极化子密度对磁场的依赖性。包含在位和长程库仑排斥的蒙特卡罗模拟展示了这如何导致正磁阻和负磁阻。根据双极化子形成或解离与跳跃速率之间的分支比，可得到与实验结果高度吻合的两种不同线形。
