Showing papers on "Charge transfer insulators published in 1997"
TL;DR: In this paper, high-resolution L 2,3 X-ray absorption spectra from nickel(II) oxides (NiO, NiFe 2 O 4 and NiGa 2O 4 ) and compared with those obtained from Xray photoelectron spectroscopy are presented.
59 citations
TL;DR: In this paper, the effects of strong magnetic field on Kondo insulators were studied and it was shown that the energy gap closes and the first order transition from insulator to metal takes place at a critical field H c.
Abstract: In order to study the effects of strong magnetic field on Kondo insulators, we calculate magnetization curves and single-particle excitation spectra of the periodic Anderson model at half-filling under finite magnetic field by using the self-consistent second-order perturbation theory combined with the local approximation which becomes exact in the limit of infinite spatial dimensions. Without magnetic field, the system behaves as an insulator with an energy gap, describing the Kondo insulators. By applying magnetic field to f-electrons, we found that the energy gap closes and the first order transition from insulator to metal takes place at a critical field H c . The magnetization curve shows a jump at H c . These are consistent with our previous study in terms of the exact diagonalization. Relationship to the experiments on YbB 12 and some other Kondo insulators is discussed.
18 citations
TL;DR: In this paper, the authors show that charge injection at a field-enhancing defect is associated with an instability of the insulating state or with bistability of both the insulator and the charged state.
Abstract: We show that in a macroscopic perfect insulator, charge injection at a field-enhancing defect is associated with an instability of the insulating state or with bistability of the insulating and the charged state. The effect of a nonlinear carrier mobility is emphasized. The formation of the charged state is governed by two different processes with clearly separated time scales. First, due to a fast growth of a charge-injection mode, a localized charge cloud forms near the injecting defect (or contact). Charge injection stops when the field enhancement is screened below criticality. Secondly, the charge slowly redistributes in the bulk. The linear instability mechanism and the final charged steady state are discussed for a simple model and for cylindrical and spherical geometries. The theory explains an experimentally observed increase of the critical electric field with decreasing size of the injecting contact. Numerical results are presented for dc and ac biased insulators.
12 citations
TL;DR: In this paper, the Lanczos method and the self-consistent second-order perturbation theory were used to solve the effective impurity problem of the Kondo insulators.
Abstract: To investigate the properties of the Kondo insulators, we calculate magnetization curves and single-particle excitation spectra for the periodic Anderson model in the limit of large spatial dimensions under finite magnetic field. The effective impurity problem was solved by the Lanczos method and the self-consistent second-order perturbation theory. At half-filling, the system behaves as an insulator with an energy gap, describing the Kondo insulators. By applying magnetic field to f-electrons, we found the first-order transition from insulator to metal at a critical field Hc, which is of trder of the Kondo temperature. The magnetization curves jump up at Hc. Relationship to the experiments on YbB12 is discussed.
1 citations
TL;DR: In this paper, the phonon-assisted absorption in the quantum spin chain model of one-dimensional Mott insulators including CuO chains is studied theoretically. And the mid-infrared absorption spectrum has an asymmetric cusp-like singularity.
Abstract: Optical spectra of one-dimensional Mott insulators including CuO chains are studied theoretically. The midinfrared absorption spectrum has an asymmetric cusp-like singularity. We analyze this spectrum in terms of the phonon-assisted absorption in the quantum spin chain model. A good agreement between theory and experiments is obtained, and the singularity is identified with the van Hove singularity of the des Cloizeaux-Pearson modes.