Collective excitations in the quasi-one-dimensional conductor K0.3MoO3

We investigate collective mode dispersions for the tight-binding dielectric matrix with two one-dimensional electron bands and the three-dimensional long-range Coulomb electron-electron interaction within the random phase approximation. The hybridized collective modes are the result of coupling between the intraband plasmon and the interband dipolar mode due to monopole-dipole Coulomb interaction. Our calculations show the existence of the renormalized plasmon mode below and the dipolar mode above the interband electron-hole quasi-continuum in the long-wavelength limit, as well as a distinct experimentally observable feature in the energy-loss function for large wavevectors in the region of interband excitations. The modes and features obtained are brought into correspondence with the data obtained from electron energy-loss spectroscopy measurements on a quasi-one-dimensional metal, the blue bronze K_0.3MoO₃.