Gunnarsson O, Han JE
Max-Planck-Institut fur Festkorperforschung, Stuttgart, Germany.
Nature. 2000 Jun 29;405(6790):1027-30. doi: 10.1038/35016512.
The electrical resistivity, p, of a metal is usually interpreted in terms of the mean free path (the average distance, l, an electron travels before it is scattered). As the temperature is raised, the resistivity increases and the apparent mean free path is correspondingly reduced. In this semi-classical picture, the mean free path cannot be much shorter than the distance, d, between two atoms. This has been confirmed for many systems and was considered to be a universal behaviour. Recently, some apparent exceptions were found, including alkali-doped fullerenes and high-temperature superconductors. However, there remains the possibility that these systems are in exotic states, with only a small fraction of the conduction electrons contributing to the conductivity; the mean free path would then have to be correspondingly larger to explain the observed resistivity. Here we report a model calculation of electron conduction in alkali-doped fullerenes, in which the electrons are scattered by intramolecular vibrations. The resistivity at large temperatures implies l << d, demonstrating that there is no fundamental principle requiring l > or = d. At high temperatures, the semi-classical picture breaks down, and the electrons cannot be described as quasiparticles.
金属的电阻率p通常根据平均自由程（电子在被散射前行进的平均距离l）来解释。随着温度升高，电阻率增加，表观平均自由程相应减小。在这种半经典图像中，平均自由程不会比两个原子之间的距离d短太多。这已在许多系统中得到证实，并被认为是一种普遍行为。最近，发现了一些明显的例外情况，包括碱掺杂富勒烯和高温超导体。然而，这些系统仍有可能处于奇异状态，只有一小部分传导电子对电导率有贡献；那么平均自由程就必须相应地更大，以解释观测到的电阻率。在此，我们报告了碱掺杂富勒烯中电子传导的模型计算，其中电子被分子内振动散射。高温下的电阻率意味着l << d，表明不存在要求l ≥ d的基本原理。在高温下，半经典图像失效，电子不能被描述为准粒子。
