Magnetic Field Effect in One-Dimensional Charge Ordering Systems

We study the effects of an external magnetic field on charge ordering in the one-dimensional extended Hubbard model at quarter filling by the quantum Monte Carlo method. We find that the Zeeman coupling enhances the charge order correlation, which is prominent when the system is located in the critical regime near the charge ordering transition at zero magnetic field. This behavior is interpreted in terms of the crossover to the fully spin-polarized limit where the model is exactly solvable. Furthermore, by incorporating the interchain Coulomb repulsion, we show that the charge-ordering transition temperature is increased by the magnetic field. We also discuss the relevance of our results to magnetoresistance effects observed in molecular conductors.