Inspired from an experimentally examined organic conductor, a novel mechanism for negative magnetoresistance is proposed for repulsively interacting electrons on a lattice whose band dispersion contains a flat portion (a flat bottom below a dispersive part here). When the Fermi level lies in the flat part, the electron correlation should cause ferromagnetic spin fluctuations to develop with an enhanced susceptibility. A relatively small magnetic field will then shift the majority-spin Fermi level to the dispersive part, resulting in a negative magnetoresistance. We have actually confirmed the idea by calculating the conductivity in magnetic fields, with the fluctuation exchange approximation, for the repulsive Hubbard model on a square lattice having a large second nearest-neighbor hopping.
@article{arxiv.cond-mat/9911154,
title = {An electron correlation originated negative magnetoresistance in a system having a partly flat band},
author = {Ryotaro Arita and Kazuhiko Kuroki and Hideo Aoki},
journal= {arXiv preprint arXiv:cond-mat/9911154},
year = {2009}
}
Comments
RevTex, 5 figures in Postscript, to be published in Phys. Rev. B