Tuning the electronic structure from charge-transfer insulator to Mott-Hubbard and Peierls insulators in one-dimensional halogen-bridged mixed-metal compounds

Abstract

The electronic structures of one-dimensional (1D) halogen-bridged mixed-metal compounds, $[{\mathrm{Ni}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}{(\mathrm{chxn})}_{2}X]{X}_{2}$ ($\mathrm{chxn}$= cyclohexanediamine; $X=\mathrm{Cl}$,$\mathrm{Br}$; $0\ensuremath{\leqslant}x\ensuremath{\leqslant}1$), are investigated through optical and magnetic measurements. The results reveal that the system changes from charge-transfer (CT) insulator to Mott-Hubbard (MH) insulator at around $x\ensuremath{\sim}0.3$, and from MH insulator to Peierls insulator at $x\ensuremath{\sim}0.9$ with increasing $x$. From the analysis of optical conductivity spectra using the 1D two-band extended Peierls-Hubbard model, electronic parameters such as Coulomb repulsion energy, $pd$ hybridization, CT energy, and electron-lattice interaction are determined.