arXiv subjects

G. Kotliar

Publications and source records attributed to G. Kotliar.

At least 91 records · Page 5Linked to original sources

arXiv2010

Self consistent GW determination of the interaction strength: application to the iron arsenide superconductors

We introduce a first principles approach to determine the strength of the electronic correlations based on the fully self consistent GW approximation. The approach provides a seamless interface with dynamical mean field theory, and gives good results for well studied correlated materials such as NiO. Applied to the recently discovered iron arsenide materials, it accounts for the noticeable correlation features observed in optics and photoemission while explaining the absence of visible satellites in X-ray absorption experiments and other high energy spectroscopies.

cond-mat.str-el↗

arXiv2009

Kondo effect and conductance of nanocontacts with magnetic impurities

We study the impact of dynamical correlations on the electronic structure and coherent transport properties of Cu nanocontacts hosting a single magnetic impurity (Ni,Co,Fe) in the contact region. The strong dynamical correlations of the impurity 3d-electrons are fully taken into account by combining density functional calculations with a dynamical treatment of the impurity 3d-shell in the one-crossing approximation. We find that dynamical correlations give rise to the Kondo effect and lead to Fano features in the coherent transport characteristics similar to those observed in related experiments.

cond-mat.mes-hall↗

arXiv2009

Critical behavior at Mott-Anderson transition: a TMT-DMFT perspective

We present a detailed analysis of the critical behavior close to the Mott-Anderson transition. Our findings are based on a combination of numerical and analytical results obtained within the framework of Typical-Medium Theory (TMT-DMFT) - the simplest extension of dynamical mean field theory (DMFT) capable of incorporating Anderson localization effects. By making use of previous scaling studies of Anderson impurity models close to the metal-insulator transition, we solve this problem analytically and reveal the dependence of the critical behavior on the particle-hole symmetry. Our main result is that, for sufficiently strong disorder, the Mott-Anderson transition is characterized by a precisely defined two-fluid behavior, in which only a fraction of the electrons undergo a "site selective" Mott localization; the rest become Anderson-localized quasiparticles.

cond-mat.str-el↗

arXiv2009

Pseudogap opening and formation of Fermi arcs as an orbital-selective Mott transition in momentum space

We present an approach to the normal state of cuprate superconductors which is based on a minimal cluster extension of dynamical mean-field theory. Our approach is based on an effective two-impurity model embedded in a self-consistent bath. The two degrees of freedom of this effective model can be associated to the nodal and antinodal regions of momentum space. We find a metal-insulator transition which is selective in momentum space: At low doping quasiparticles are destroyed in the antinodal region, while they remain protected in the nodal region, leading to the formation of apparent Fermi arcs. We compare our results to tunneling and angular-resolved photoemission experiments on cuprates. At very low energy, a simple description of this transition can be given using rotationally invariant slave bosons.

cond-mat.str-el↗

arXiv2009

Coherence-incoherence crossover in the normal state of iron-oxypnictides and importance of the Hund's rule coupling

A new class of high temperature superconductors based on iron and arsenic was recently discovered, with superconducting transition temperature as high as 55 K. Here we show, using microscopic theory, that the normal state of the iron pnictides at high temperatures is highly anomalous, displaying a Curie Weiss susceptibility and a linear temperature dependence of the resistivity. Below a coherence scale T*, the resistivity sharply drops and susceptibility crosses over to Pauli-like temperature dependence. Remarkably, the coherence-incoherence crossover temperature is a very strong function of the strength of the Hund's rule coupling J_Hund. On the basis of the normal state properties, we estimate J_Hund to be 0.35-0.4 eV. In the atomic limit, this value of J_Hund leads to the critical ratio of the exchange constants J_1/J_2~2. While normal state incoherence is in common to all strongly correlated superconductors, the mechanism for emergence of the incoherent state in iron-oxypnictides, is unique due to its multiorbital electronic structure.

cond-mat.supr-con↗

arXiv2008

Combining the Hybrid Functional Method with Dynamical Mean-Field Theory

We present a new method to compute the electronic structure of correlated materials combining the hybrid functional method with the dynamical mean-field theory. As a test example of the method we study cerium sesquioxide, a strongly correlated Mott-band insulator. The hybrid functional part improves the magnitude of the pd-band gap which is underestimated in the standard approximations to density functional theory while the dynamical mean-field theory part splits the 4f-electron spectra into a lower and an upper Hubbard band.

cond-mat.mtrl-sci↗

arXiv2008

Coulomb Correlations and the Wigner-Mott Transition

Strong correlation effects, such as a dramatic increase in the effective mass of the carriers of electricity, recently observed in the low density electron gas have provided spectacular support for the existence of a sharp metal-insulator transitions in dilute two dimensional electron gases. Here we show that strong correlations, normally expected only for narrow integer filled bands, can be effectively enhanced even far away from integer filling, due to incipient charge ordering driven by non-local Coulomb interactions. This general mechanism is illustrated by solving an extended Hubbard model using dynamical mean-field theory. Our findings account for the key aspects of the experimental phase diagram, and reconcile the early view points of Wigner and Mott. The interplay of short range charge order and local correlations should result in a three peak structure in the spectral function of the electrons which should be observable in tunneling and optical spectroscopy.

cond-mat.str-el↗

arXiv2008

Cluster Dynamical Mean Field Theory of the Mott Transition

We address the nature of the Mott transition in the Hubbard model at half-filling using cluster Dynamical Mean Field Theory (DMFT). We compare cluster DMFT results with those of single site DMFT. We show that inclusion of the short range correlations on top of the on-site correlations, already treated exactly in single site DMFT, do not change the nature of the transition between the paramagnetic metal and the paramagnetic Mott insulator, which remains first order. However, the short range correlations reduce substantially the critical $U$ and modify the shape of transition lines. Moreover, they lead to very different physical properties of the metallic and insulating phases near the transition, in particular in the region of the phase diagram where the two solutions coexist. Approaching the transition from the metallic side, we find an anomalous metallic state with very low coherence scale at temperatures as low as $T=0.01t$. The insulating state is characterized by the relatively narrow Mott gap with pronounced peaks at the gap edge.

cond-mat.str-el↗

arXiv2008

X-ray absorption branching ratio in actinides: LDA+DMFT approach

To investigate the x-ray absorption (XAS) branching ratio from the core 4d to valence 5f states, we set up a theoretical framework by using a combination of density functional theory in the local density approximation and Dynamical Mean Field Theory (LDA+DMFT), and apply it to several actinides. The results of the LDA+DMFT reduces to the band limit for itinerant systems and to the atomic limit for localized f electrons, meaning a spectrum of 5f itinerancy can be investigated. Our results provides a consistent and unified view of the XAS branching ratio for all elemental actinides, and is in good overall agreement with experiments.

cond-mat.mtrl-sci↗

arXiv2008

A new family of iron pnictides: BaFeAs2 and BaFeSb2

We investigate the structural, electronic, and magnetic properties of the hypothetical compound BaFePn2 (Pn = As and Sb), which is isostructural to the parent compound of the high temperature superconductor LaFeAsO1-xFx. Using density functional theory, we show that the Fermi surface, electronic structure and the spin density wave instability of BaFePn2 are very similar to the Fe based superconductors. Additionally, there are very dispersive metallic bands of a spacer Pn layer, which are almost decoupled from FePn layer. Our results show that experimental study of BaFePn2 can test the role of charge and polarization fluctuation, importance of two dimensionality in mechanism of superconductivity.

cond-mat.supr-con↗

arXiv2008

Valence-Bond Dynamical Mean-Field Theory of Doped Mott Insulators with Nodal/Antinodal Differentiation

We introduce a valence-bond dynamical mean-field theory of doped Mott insulators. It is based on a minimal cluster of two orbitals, each associated with a different region of momentum space and hybridized to a self-consistent bath. The low-doping regime is characterized by singlet formation and the suppression of quasiparticles in the antinodal regions, leading to the formation of Fermi arcs. This is described in terms of an orbital-selective transition in reciprocal space. The calculated tunneling and photoemission spectra are consistent with the phenomenology of the normal state of cuprates. We derive a low-energy description of these effects using a generalization of the slave-boson method.

cond-mat.str-el↗

arXiv2008

Screening of magnetic moments in PuAm alloy : LDA+DMFT study

The puzzling absence of Pu magnetic moments in a PuAm environment is explored using the self-consistent Dynamical Mean Field Theory (DMFT) calculations in combination with the Local Density Approximation. We argue that delta-Pu -Am alloys provide an ideal test bed for investigating the screening of moments from the single impurity limit to the dense limit. Several important effects can be studied: volume expansion, shift of the bare Pu on-site f energy level, and the reduction of the hybridization cloud resulting from the collective character of the Kondo effect in the Anderson lattice. These effects compensate each other and result in a coherence scale, which is independent of alloy composition, and is around 800K. We emphasize the role of the DMFT self-consistency condition, and multiplet splittings in Pu and Am atoms, in order to capture the correct value of the coherence scale in the alloy.

cond-mat.str-el↗

arXiv2008

Electronic coherence in $δ$-Pu: A DMFT study

A combination of Density Functional Theory and the Dynamical Mean Field theory (DMFT) is used to calculate the magnetic susceptibility, heat capacity, and the temperature dependence of the valence band photoemission spectra. The continuous-time hybridization expansion quantum Monte-Carlo is utilized to provide the first approximation-free DMFT solution of \emph{fcc} $δ$-Pu which includes the full rotationally-invariant exchange interaction. We predict that $δ$-Pu has a Pauli-like magnetic susceptibility near ambient temperature, as in experiment, indicating that electronic coherence causes the absence of local moments. Additionally, We show that volume expansion causes a crossover from incoherent to coherent electronic behavior at increasingly lower temperatures.

cond-mat.str-el↗

arXiv2008

Correlated electronic structure of LaOFeAs

We compute the electronic structure, momentum resolved spectral function and optical conductivity of the new superconductor LaO$_{1-x}$F$_x$FeAs within the combination of the Density functional theory and the Dynamical Mean Field Theory. We find that the compound in the normal state is a strongly correlated metal and the parent compound is a bad metal at the verge of the metal insulator transition. We argue that the superconductivity is not phonon mediated.

cond-mat.str-el↗

arXiv2008

Sum-rules for Raman scattering off strongly correlated electron systems

We investigate sum-rules applying to the Raman intensity in a strongly correlated system close to the Mott transition. Quite generally, it can be shown that, provided the frequency integration is performed up to a cutoff smaller than the upper Hubbard band, a sum-rule applies to the non-resonant Raman signal of a doped Mott insulator, resulting in an integrated intensity which is proportional to the doping level. We provide a detailed derivation of this sum-rule for the t-J model, for which the frequency cutoff can be taken to infinity and an unrestricted sum-rule applies. A quantitative analysis of the sum-rule is also presented for the d-wave superconducting phase of the t-J model, using slave boson methods. The case of the Hubbard model is studied in the framework of dynamical mean-field theory, with special attention to the cutoff dependence of the restricted sum-rule, and also to the intermediate coupling regime. The sum-rule investigated here is shown to be consistent with recent experimental data on cuprate superconductors, reporting measurements of Raman scattering intensities on an absolute scale.

cond-mat.str-el↗

arXiv2008

Nodal/Antinodal Dichotomy and the Two Gaps of a Superconducting Doped Mott Insulator

We study the superconducting state of the hole-doped two-dimensional Hubbard model using Cellular Dynamical Mean Field Theory, with the Lanczos method as impurity solver. In the under-doped regime, we find a natural decomposition of the one-particle (photoemission) energy-gap into two components. The gap in the nodal regions, stemming from the anomalous self-energy, decreases with decreasing doping. The antinodal gap has an additional contribution from the normal component of the self-energy, inherited from the normal-state pseudogap, and it increases as the Mott insulating phase is approached.

cond-mat.str-el↗

arXiv2008

Modelling the Localized to Itinerant Electronic Transition in the Heavy Fermion System CeIrIn5

We address the fundamental question of crossover from localized to itinerant state of a paradigmatic heavy fermionmaterial CeIrIn5. The temperature evolution of the one electron spectra and the optical conductivity is predicted from first principles calculation. The buildup of coherence in the form of a dispersive many body feature is followed in detail and its effects on the conduction electrons and optical conductivity of the material is revealed. We find multiple hybridization gaps and link them to the crystal structure of the material. Our theoretical approach explains the multiple peak structures observed in optical experiments and the sensitivity of CeIrIn5 to substitutions of the transition metal element and may provide a microscopic basis for the more phenomenological descriptions currently used to interpret experiments in heavy fermion systems.

cond-mat.str-el↗

arXiv2007

Anomalous superconductivity and its competition with antiferromagnetism in doped Mott insulators

Proximity to a Mott insulating phase is likely to be an important physical ingredient of a theory that aims to describe high-temperature superconductivity in the cuprates. Quantum cluster methods are well suited to describe the Mott phase. Hence, as a step towards a quantitative theory of the competition between antiferromagnetism (AFM) and d-wave superconductivity (SC) in the cuprates, we use Cellular Dynamical Mean Field Theory to compute zero temperature properties of the two-dimensional square lattice Hubbard model. The d-wave order parameter is found to scale like the superexchange coupling J for on-site interaction U comparable to or larger than the bandwidth. The order parameter also assumes a dome shape as a function of doping while, by contrast, the gap in the single-particle density of states decreases monotonically with increasing doping. In the presence of a finite second-neighbor hopping t', the zero temperature phase diagram displays the electron-hole asymmetric competition between antiferromagnetism and superconductivity that is observed experimentally in the cuprates. Adding realistic third-neighbor hopping t'' improves the overall agreement with the experimental phase diagram. Since band parameters can vary depending on the specific cuprate considered, the sensitivity of the theoretical phase diagram to band parameters challenges the commonly held assumption that the doping vs T_{c}/T_{c}^{max} phase diagram of the cuprates is universal. The calculated ARPES spectrum displays the observed electron-hole asymmetry. Our calculations reproduce important features of d-wave superconductivity in the cuprates that would otherwise be considered anomalous from the point of view of the standard BCS approach.

cond-mat.str-el↗