Local magnetic susceptibility, spin dynamics, and charge order in the quasi-one-dimensional conductor β-Li_(0.33)V_2O_5 investigated by site-selective ~(51)V NMR

摘要

~(51)V NMR measurements have been conducted on a single crystal of the quasi-one-dimensional conductor β-Li_(0.33)V_2O_5 which undergoes a metal-insulator (MI) transition at TMI ～ 170 K. In the metallic phase, we obtain ~(51)V Knight shift and electric field gradient tensors. From the analysis of the ~(51)V Knight shifts, we find that the charge disproportionation appears even in the metallic state and the electronic structure is represented within a model of weakly coupled ladders containing two types of ladders with distinct carrier densities. Based on the ~(51)V nuclear spin-lattice relaxation rate, we discuss the spin dynamics within the one-dimensional electron gas model. From the analysis of several nonmagnetic V~(5+) spectra observed in the insulating phase, we propose a possible charge-order pattern which has a superlattice modulation larger than those in other family members of β-A_(0.33)V_2O_5 (A = Na and Ag). Finally, we discuss the A-ion dependence of the electronic structure, the charge disproportionation, and the charge order in β-A_(0.33)V_2O_5.