Correlation Effect on Optical Absorption in One-Dimensional Peierls-Hubbard Systems

Abstract

Effects of the electron correlation on the opticalabsorption due to inter-band transition (CT absorption) and due tonon-linear excitations (mid-gap absorption) in one-dimensionalPeierls-Hubbard CDW systems are studied by using the exactdiagonalization method. The correlation effect of on-site repulsion Uis fairly small for both the CT and the mid-gap absorption except inthe boundary region between the CDW and AF phases while thecorrelation effect of inter-site repulsion V is significant for boththe transitions. With increasing V the CT transition is suppressed andthe exciton transition grows. As to the mid-gap absorption theintensities of absorption associated with the transitions from (or to)a defect state of the non-linear excitations to (or from) aconduction- or valence-band state are enhanced strongly by the effectof V. The absorption spectrum in the AF state is also calculated. Onlythe lowest optically-allowed state has a large oscillator strength andhence the absorption spectrum in the AF state is very sharp comparedwith the CT transition in the CDW state.