Biomedical subjects

G Kotliar

Publications and source records attributed to G Kotliar.

At least 19 recordsLinked to original sources

PubMed2006

Local self-energy approach for electronic structure calculations.

Using a novel self-consistent implementation of Hedin's perturbation theory, we calculate space- and energy-dependent self-energy for a number of materials. We find it to be local in real space and rapidly convergent on second- to third-nearest neighbors. Corrections beyond are evaluated and shown to be completely localized within a single unit cell. This can be viewed as a fully self-consistent implementation of the dynamical mean field theory for electronic structure calculations of real solids using a perturbative impurity solver.

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PubMed2005

Dynamical breakup of the fermi surface in a doped Mott insulator.

The evolution from an anomalous metallic phase to a Mott insulator within the two-dimensional Hubbard model is investigated by means of the cellular dynamical mean-field theory. We show that approaching the density-driven Mott metal-insulator transition the Fermi surface is strongly renormalized and the quasiparticle description breaks down in a very anisotropic fashion. Regions where the quasiparticles are strongly scattered (hot spots) and regions where the scattering rate is relatively weak (cold spot) form irrespective of whether the parent insulator has antiferromagnetic long-range order, while their location is not universal and is determined by the interplay of the renormalization of the scattering rate and the Fermi surface shape.

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PubMed2005

Mott transition and Kondo screening in f-electron metals.

We study how a finite hybridization between a narrow correlated band and a wide conduction band affects the Mott transition. At zero temperature, the hybridization is found to be a relevant perturbation, so that the Mott transition is suppressed by Kondo screening. In contrast, a first-order transition remains at finite temperature, separating a local-moment phase and a Kondo-screened phase. The first-order transition line terminates in two critical end points. Implications for experiments on f-electron materials such as the cerium alloy Ce0.8La0.1Th0.1 are discussed.

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PubMed2005

Superconductivity in the americium metal as a function of pressure: probing the Mott transition.

High-pressure measurements of the resistivity of americium metal are reported to 27 GPa and down to temperatures of 0.4 K. The unusual dependence of the superconducting temperature (T(c)) on pressure is deduced. The critical field [H(c)(0) extrapolated to T=0] increases dramatically from 0.05 to approximately 1 T as the pressure is increased, suggesting that the type of superconductivity is changing as pressure increases. At pressures of approximately 16 GPa the 5f electrons of Am are changing from localized to itinerant, and the crystal structure also transforms to a complex one. The role of a Mott-type transition in the development of the peak in T(c) above 16 GPa is postulated.

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PubMed2004

A first-order Mott transition in LixCoO2.

Despite many years of experimental searches for a first-order Mott transition in crystalline-doped semiconductors, none have been found. Extensive experimental work has characterized a first-order metal-insulator transition in Li(x)CoO(2), the classic material for rechargeable Li batteries, with a metallic state for x < 0.75 and insulating for x > 0.95. Using density functional theory calculations on large supercells, we identify the mechanism of this hereto anomalous metal-insulator transition as a Mott transition of impurities. Density functional theory demonstrates that for dilute Li-vacancy concentrations, the vacancy binds a hole and forms impurity states yielding a Mott insulator. The unique feature of Li(x)CoO(2) as compared with traditional doped semiconductors, such as Si:P, is the high mobility of the Li vacancies, which allows them to rearrange into two distinct phases at the temperature of the metal-insulator transition.

Cobalt↗

PubMed2004

Nonlocal Coulomb interactions and metal-insulator transition in Ti2O3: a cluster LDA+DMFT approach.

We present an ab initio quantum theory of the metal-insulator transition in Ti2O3. The recently developed cluster LDA+DMFT scheme is applied to describe the many-body features of this compound. The conventional single site DMFT cannot reproduce a low temperature insulating phase for any reasonable values of the Coulomb interaction. We show that the nonlocal Coulomb interactions and the strong chemical bonding within the Ti-Ti pair is the origin of the small gap insulating ground state of Ti2O3.

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PubMed2004

Cluster dynamical mean field analysis of the mott transition.

We investigate the Mott transition using a cluster extension of dynamical mean field theory (DMFT). In the absence of frustration we find no evidence for a finite temperature Mott transition. Instead, in a frustrated model, we observe signatures of a finite temperature Mott critical point in agreement with experimental studies of kappa organics and with single-site DMFT. As the Mott transition is approached, a clear momentum dependence of the electron lifetime develops on the Fermi surface with the formation of cold regions along the diagonal direction of the Brillouin zone. Furthermore, the variation of the effective mass is no longer equal to the inverse of the quasiparticle residue, as in DMFT, and is reduced approaching the Mott transition.

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PubMed2004

Role of hybridization in NaxCoO2 and the effect of hydration.

Density functional theory is used to understand the electronic properties of Na(1/3)CoO2 and Na(1/3)CoO2(H2O)(4/3). Comparing the charge density of CoO2 and the Na doped phases indicates that doping does not simply add electrons to the t(2g) states. In fact, the electron added in the t(2g) state is dressed by hole density in the e(g) state and electron density in the oxygen states via rehybridization. In order to fully understand this phenomenon, a simple extension of the Hubbard Hamiltonian is proposed and solved using the dynamical mean-field theory. This model confirms that the rehybridization is driven by a competition between the on-site Coulomb interaction and the hybridization, and results in an effective screening of the low-energy excitations. Finally, we show that hydration causes the electronic structure to become more two dimensional.

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PubMed2003

Disorder screening in strongly correlated systems.

Electron-electron interactions generally reduce the low temperature resistivity due to the screening of the impurity potential by the electron gas. In the weak-coupling limit, the magnitude of this screening effect is determined by the thermodynamic compressibility which is proportional to the inverse screening length. We show that when strong correlations are present, although the compressibility is reduced, the screening effect is nevertheless strongly enhanced. This phenomenon is traced to the same nonperturbative Kondo-like processes that lead to strong mass enhancements, but which are absent in weak-coupling approaches. We predict metallicity to be strongly stabilized in an intermediate regime where the interactions and the disorder are of comparable magnitude.

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PubMed2003

Calculated phonon spectra of plutonium at high temperatures.

We constructed computer-based simulations of the lattice dynamical properties of plutonium using an electronic structure method, which incorporates correlation effects among the f-shell electrons and calculates phonon spectra at arbitrary wavelengths. Our predicted spectrum for the face-centered cubic delta phase agrees well with experiments in the elastic limit and explains unusually large shear anisotropy of this material. The spectrum of the body-centered cubic phase shows an instability at zero temperature over a broad region of the wave vectors, indicating that this phase is highly anharmonic and can be stabilized at high temperatures by its phonon entropy.

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PubMed2003

Linear response calculations of lattice dynamics in strongly correlated systems.

We introduce a new linear response method to study the lattice dynamics of materials with strong correlations. It is based on a combination of dynamical mean field theory of strongly correlated electrons and the local density functional theory of electronic structure. We apply the method to study the phonon dispersions of Mott insulators NiO and MnO in their paramagnetic insulating state not accessible by local density functionals. Our results are in good agreement with experiment.

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PubMed2002

Compressibility divergence and the finite temperature Mott transition.

In the context of the dynamical mean-field theory (DMFT) of the Hubbard model, we study the behavior of the compressibility near the density driven Mott transition at finite temperatures. We demonstrate this divergence using DMFT and quantum Monte Carlo simulations in the one-band and the two-band Hubbard model. We supplement this result with considerations based on the Landau theory framework, and discuss the relevance of our results to the alpha-gamma end point in cerium.

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PubMed2001

Importance of correlation effects on magnetic anisotropy in Fe and Ni.

We calculate magnetic anisotropy energy of Fe and Ni by taking into account the effects of strong electronic correlations, spin-orbit coupling, and noncollinearity of intra-atomic magnetization. The LDA+U method is used and its equivalence to dynamical mean-field theory in the static limit is emphasized. Both experimental magnitude of magnetic anisotropy energy and direction of magnetization are predicted correctly near U = 1.9 eV, J = 1.2 eV for Ni and U = 1.2 eV, J = 0.8 eV for Fe. Correlations modify the one-electron spectra which are now in better agreement with experiments.

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PubMed2001

Finite-temperature magnetism of transition metals: an ab initio dynamical mean-field theory.

We present an ab initio quantum theory of the finite-temperature magnetism of iron and nickel. A recently developed technique which combines dynamical mean-field theory with realistic electronic structure methods successfully describes the many-body features of the one electron spectra and the observed magnetic moments below and above the Curie temperature.

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PubMed2001

Correlated electrons in delta-plutonium within a dynamical mean-field picture.

Given the practical importance of metallic plutonium, there is considerable interest in understanding its fundamental properties. Plutonium undergoes a 25 per cent increase in volume when transformed from its alpha-phase (which is stable below 400 K) to the delta-phase (stable at around 600 K), an effect that is crucial for issues of long-term storage and disposal. It has long been suspected that this unique property is a consequence of the special location of plutonium in the periodic table, on the border between the light and heavy actinides-here, electron wave-particle duality (or itinerant versus localized behaviour) is important. This situation has resisted previous theoretical treatment. Here we report an electronic structure method, based on dynamical mean-field theory, that enables interpolation between the band-like and atomic-like behaviour of the electron. Our approach enables us to study the phase diagram of plutonium, by providing access to the energetics and one-electron spectra of strongly correlated systems. We explain the origin of the volume expansion between the alpha- and delta-phases, predict the existence of a strong quasiparticle peak near the Fermi level and give a new viewpoint on the physics of plutonium, in which the alpha- and delta-phases are on opposite sides of the interaction-driven localization-delocalization transition.

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PubMed2000

Two-scale analysis of the SU(N) kondo model

We show how to resolve coherent low-energy features embedded in a broad high-energy background by use of a fully self-consistent calculation for composite particle operators. The method generalizes the formulation of Roth, which linearizes the dynamics of composite operators at any energy scale. Self-consistent equations are derived and analyzed in the case of the single-impurity SU(N) Kondo model.

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PubMed2000

Landau theory of the finite temperature mott transition

In the context of the dynamical mean-field theory of the Hubbard model, we identify microscopically an order parameter for the finite temperature Mott end point. We derive a Landau functional of the order parameter. We then use the order parameter theory to elucidate the singular behavior of various physical quantities which are experimentally accessible.

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PubMed2000

Ground state theory of delta-Pu

Correlation effects are important for making predictions in the delta phase of Pu. Using a realistic treatment of the intra-atomic Coulomb correlations we address the long-standing problem of computing ground state properties. The equilibrium volume is obtained in good agreement with experiment when taking into account Hubbard U of the order 4 eV. For this U, the calculation predicts a 5f(5) atomiclike configuration with L = 5, S = 5/2, and J = 5/2 and shows a nearly complete compensation between spin and orbital magnetic moments.

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