Showing papers on "Charge transfer insulators published in 2001"
TL;DR: In this paper, the authors proposed an orbital ordering of complex orbitals (linear superposition of basic orbitals with complex coefficients) for doped Mott insulators with Jahn-Teller ions.
Abstract: Orbital ordering, often observed in Mott insulators with orbital degeneracy, is usually supposed to disappear with doping, e.g., in the ferromagnetic metallic phase of manganites. We propose that the orbital ordering of a novel type may exist in such a situation: there may occur an orbital ordering of complex orbitals (linear superposition of basic orbitals ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ and ${d}_{{z}^{2}}$ with complex coefficients). Despite the perfect orbital ordering, such a state still retains cubic symmetry and thus would not induce any structural distortion. This state can resolve many problems in the physics of colossal magnetoresistance manganites and can also exist in other doped Mott insulators with Jahn-Teller ions.
62 citations
TL;DR: It is shown that only few particle processes contribute significantly to the optical conductivity over a wide range of frequencies and that the bare perturbative regime is recovered only at very large energies.
Abstract: We calculate the optical conductivity of one-dimensional Mott insulators at low energies using a field theory description. The square root singularity at the optical gap, characteristic of band insulators, is generally absent and appears only at the Luther-Emery point. We also show that only few particle processes contribute significantly to the optical conductivity over a wide range of frequencies and that the bare perturbative regime is recovered only at very large energies. We discuss possible applications of our results to quasi-one-dimensional organic conductors.
47 citations
TL;DR: This paper presents a novel mechanism that can enhance the hyperpolarizability (gamma) of charge-transfer-Mott insulators, jointly Delta and U, which may suggest a conceptually new paradigm to explore an even larger optical nonlinearity.
Abstract: Neither pure Mott insulators nor pure charge-transfer insulators have ever been considered as a possible candidate for nonlinear optical (NLO) materials since individually neither the strong correlation (U) nor the large charge transfer (Delta) is favorable to the NLO response However, in their composites, charge-transfer-Mott insulators, jointly Delta and U can enhance the hyperpolarizability (gamma) by guiding the ground states into the antiferromagnetic phase and the excited states into the charge-transfer phase These Delta and U that maximize gamma form a unique golden Delta-U line, on which the recently observed giant nonlinear optical effect is just a single point, whose physical origin is that the system is driven into a phase-separated region for the ground and excited states This novel mechanism may suggest a conceptually new paradigm to explore an even larger optical nonlinearity
20 citations
10 citations
TL;DR: In this article, the charge sector of one dimensional Mott insulators can be described in terms of a quantum Sine-Gordon model (SGM) using exact results derived from integrability, and it is possible to determine dynamical properties like the frequency dependent optical conductivity.
Abstract: At low energies the charge sector of one dimensional Mott insulators can be described in terms of a quantum Sine-Gordon model (SGM). Using exact results derived from integrability it is possible to determine dynamical properties like the frequency dependent optical conductivity. We compare the exact results to perturbation theory and renormalisation group calculations. We also discuss the application of our results to experiments on quasi-ID organic conductors.
9 citations
TL;DR: In this paper, the spin-charge separation and large on-site Coulomb interaction play a crucial role in obtaining degenerate dipole-allowed and dipoleforbidden states in the photoexcited states.
8 citations
TL;DR: In this article, it is shown that Hund's rule concerning the high-spin state in transition metal (TM) compounds does not always hold at high pressures, resulting in a spin-crossover and collapse of the magnetic state for even-valence TM ions and for a decline of magnetic exchange for oddvalence ions.
Abstract: Combining the techniques of Mossbauer spectroscopy, synchrotron XRD, and electrical resistivity in conjunction with diamond-anvil cells has enabled us to discover and study new phenomena in magnetism and electronic correlations at high density. It is shown that Hund's rule concerning the high-spin state in transition metal (TM) compounds does not always hold at high pressures, resulting in a spin-crossover and collapse of the magnetic state for even-valence TM ions and for a decline of the magnetic exchange for odd-valence ions. This mechanism is in competition with the breakdown of the d–d electron correlation (Mott transition) in pressure transformation of Mott insulators into normal metals. The experimental issues are described and a few examples of studies of breakdown of the Mott-Hubbard state at very high pressures are presented.
7 citations
TL;DR: In this paper, the problem of charge transport in one-dimensional insulators via semiclassical and perturbative renormalization group methods was investigated, and it was shown that nonlinear collective modes such as polarons and solitons are responsible for transport.
Abstract: In this work we investigate charge transport in one-dimensional insulators via semiclassical and perturbative renormalization group methods. We consider the problem of electron-electron, electron-phonon and electron-two-level system interactions. We show that nonlinear collective modes such as polarons and solitons are responsible for transport. We find a new excitation in the Mott insulator: the polaronic soliton. We discuss fhe differences between band and Mott insulators in terms of their spin spectrum and obtain the charge and spin gaps in each one of these systems. We show that electron-electron interactions provide strong renormalizations of the energy scales in the problem.
3 citations
TL;DR: In this article, a two-subband model was used to study the energy gap and the metal-insulator transition in anisotropic Kondo insulators, where a strongly correlated narrow f band is coupled to a wide band of conduction electrons via an aisotropic hybridization, and a gapless phase was found for a range of the hybridization parameters.
Abstract: In this work we use a two-subband model to study the energy gap and the metal–insulator transition in anisotropic Kondo insulators. In this model a strongly correlated narrow f band is coupled to a wide band of conduction electrons via an anisotropic hybridization. Parametrizing the hybridization as a constant plus a k -dependent term proportional to the dispersion relation of the wide band, we found a gapless phase for a range of the hybridization parameters.
1 citations
TL;DR: In this paper, it was shown that the spin-gap and pairing correlation are enhanced if the band structure is adjusted to become flat at the Fermi level near half-filling in strongly correlated electron systems.
Journal Article•
TL;DR: In this article, the authors proposed a simple equivalent model of these distributions in order to characterize the internal residual field in a thin polymeric insulator using a frequency-based technique called focused laser intensity modulation method (FLIMM).
Abstract: As insulators are stressed with a strong electric field, they store electric charges that can be represented as space charge distributions. We propose a simple equivalent model of these distributions in order to characterize the internal residual field in a thin polymeric insulator using a frequency-based technique called focused laser intensity modulation method (FLIMM). This approach shows its ability to follow simple evolutions resulting for example from an increasing of stressing field or of the poling duration time, avoiding in a first approximation the use of complex mathematical algorithms.
TL;DR: In this paper, the authors investigated charge transport in one-dimensional (1D) insulators via semi-classical and perturbative renormalization group (RG) methods.
Abstract: In this work we investigate charge transport in one-dimensional (1D) insulators via semi-classical and perturbative renormalization group (RG) methods. We consider the problem of electron-electron, electron-phonon and electron-two-level system interactions. We show that non-linear collective modes such as polarons and solitons are reponsible for transport. We find a new excitation in the Mott insulator: the polaronic soliton. We discuss the differences between band and Mott insulators in terms of their spin spectrum and obtain the charge and spin gaps in each one of these systems. We show that electron-electron interactions provide strong renormalizations of the energy scales in the problem.