Syntheses and Properties of Single CuO2-Sheet Compounds: Charge-Transfer Gap and Charge-Doping Effect

Bond-length dependence of charge-transfer excitations and stretch phonon modes in perovskite ruthenates: Evidence of strongp–dhybridization effects

“…For cuprates and nickelates, [2][3][4][5][6] it was already known that the dimensionality, which is related to the coordination number of the oxygen atoms for the transition metal ion, should play an important role. To check this possibility, we plotted the dimensionality dependences of the ⌬ p-d values in Fig.…”

“…For cuprates, while the charge-transfer energy is partly determined by the Cu-O bond length, 1 it is also strongly influenced by the coordination number of the system or by the system dimensionality. [2][3][4] Ohta et al have demonstrated that a fairly large variation of ⌬ p-d in insulating cuprates could be well explained by ⌬V Mad . 5 For nickelates also, the change of the Madelung potential, related to the structural dimensionality, could explain the large variations of the charge-transfer energies.…”

Excitonic cluster model of strongly correlated electronic systems

“…In conclusion, we have been able to understand quantitatively the characteristics of several optical responses which depend sensitively on the relative values of t p and V . This also seems to clear up the inconsistent assignment [9] of the photo-conductivity spectrum [9,10], the absorption spectrum [3,4,9], and the large-shift RS [8]. Finally, we have resolved the mystery of the resonance-enhancement spectrum of 2-magnon RS.…”

“…This is one type of Letter to the Editor degenerate perturbation theory among the group-theoretically adapted basis states of a single particle excitation in the site representation. Indeed, the excitonic cluster model found in this paper is capable of describing quantitatively the absorption spectrum [3,4], the large-shift RS [8] and the resonance-enhancement of 2-magnon RS [1,2] as well as two-photon absorption (TPA) spectrum in cuprates of several perovskite types. At the same time we can resolve the mystery of the resonance-enhancement of 2-magnon RS, and clear up the inconsistencies among assignments of the absorption and the photoconductivity spectra [9,10] as well as the large-shift RS [8].…”

“…Optical responses of the insulating cuprates without doping originate in the charge-transfer (CT) excitation from the fully occupied O (2p σ ) electron into the empty level of Cu (3d x 2 −y 2 ) in the visible region. Therefore, the 2D network of CuO 2 plays a key role in the optical responses of perovskite-type copper oxides [3,4]. In addition to this, the electronic ground state is a well-defined antiferromagnetic (AF) insulator [5] and the low-lying elementary excitations can be well described by magnons [6] in a single layer system such as T -type (La 2 CuO 4 ) and T -type (Gd 2 CuO 4 , Nd 2 CuO 4 ) and in a double-layer system (YBa 2 Cu 3 O 6 ) (see figure 1).…”