Longitudinal and Hall conductances in model alkali fulleridesA3C60

Abstract

We have calculated the low-temperature, low-field longitudinal and transverse conductivities for various tight-binding models intended to represent the conduction band in ${A}_{3}{\mathrm{C}}_{60}$ compounds, by directly applying the Kubo-Greenwood formula to finite clusters. It turns out that the ``universal'' dependence of Hall coefficient on lattice constant found for ${\mathrm{K}}_{3}{\mathrm{C}}_{60}$ and ${\mathrm{Rb}}_{3}{\mathrm{C}}_{60}$ [L. Lu et al., Phys. Rev. Lett. 74, 1637 (1995)] cannot be accounted for by appealing to two types of disorder, one of which (merohedral disorder) has an energy scale that varies strongly with lattice constant and another of which (that we model as Anderson disorder) does not. The calculations also reveal enormous violations of Matthiessen's rule: it is even possible to decrease the resistivity by introducing merohedral disorder into a system which had only Anderson disorder.