arXiv subjects

V. Zlatic

Publications and source records attributed to V. Zlatic.

31 records · Page 2Linked to original sources

arXiv2004

F-electron spectral function of the Falicov-Kimball model in infinite dimensions: the half-filled case

The f-electron spectral function of the Falicov-Kimball model is calculated via a Keldysh-based many-body formalism originally developed by Brandt and Urbanek. We provide results for both the Bethe lattice and the hypercubic lattice at half filling. Since the numerical computations are quite sensitive to the discretization along the Kadanoff-Baym contour and to the maximum cutoff in time that is employed, we analyze the accuracy of the results using a variety of different moment sum-rules and spectral formulas. We find that the f-electron spectral function has interesting temperature dependence becoming a narrow single-peaked function for small U and developing a gap, with two broader peaks for large U.

cond-mat.str-el↗

arXiv2003

Exact solution of the Falicov-Kimball model with dynamical mean-field theory

The Falicov-Kimball model was introduced in 1969 as a statistical model for metal-insulator transitions; it includes itinerant and localized electrons that mutually interact with a local Coulomb interaction and is the simplest model of electron correlations. It can be solved exactly with dynamical mean-field theory in the limit of large spatial dimensions which provides an interesting benchmark for the physics of locally correlated systems. In this review, we develop the formalism for solving the Falicov-Kimball model from a path-integral perspective, and provide a number of expressions for single and two-particle properties. We examine many important theoretical results that show the absence of fermi-liquid features and provide a detailed description of the static and dynamic correlation functions and of transport properties. The parameter space is rich and one finds a variety of many-body features like metal-insulator transitions, classical valence fluctuating transitions, metamagnetic transitions, charge density wave order-disorder transitions, and phase separation. At the same time, a number of experimental systems have been discovered that show anomalies related to Falicov-Kimball physics [including YbInCu4, EuNi2(Si[1-x]Gex)2, NiI2 and TaxN].

cond-mat.str-el↗

arXiv2002

Kondo effect in "bad metals"

We study the low-temperature properties of a Kondo lattice using the large-N formalism. For a singular density of conduction states (DOS), we generalize the single-impurity result of Withoff and Fradkin: the strong-coupling fixed point becomes irrelevant if the DOS vanishes at the Fermi level E_F. However, for E_F close enough to the singularity, and close to half-filling, the Kondo temperature, $T_K$, can become much smaller than the characteristic Fermi liquid scale. At T=0, a meta-magnetic transition occurs at the critical magnetic field H_c ~ (k_B/mu_B) T_K. Our results provide a qualitative explanation for the behavior of the YbInCu_4 compound below the valence-change transition.

cond-mat.str-el↗

arXiv2002

Optimizing thermal transport in the Falicov-Kimball model: binary-alloy picture

We analyze the thermal transport properties of the Falicov-Kimball model concentrating on locating regions of parameter space where the thermoelectric figure-of-merit ZT is large. We focus on high temperature for power generation applications and low temperature for cooling applications. We constrain the static particles (ions) to have a fixed concentration, and vary the conduction electron concentration as in the binary-alloy picture of the Falicov-Kimball model. We find a large region of parameter space with ZT>1 at high temperature and we find a small region of parameter space with ZT>1 at low temperature for correlated systems, but we believe inclusion of the lattice thermal conductivity will greatly reduce the low-temperature figure-of-merit.

cond-mat.str-el↗

arXiv2001

Thermoelectric power of Cerium and Ytterbium intermetallics

Temperature dependence S(T) of the thermoelectric power of metallic systems with cerium and ytterbium ions exhibits some characteristic features, which can be used to classify these systems into distinct categories. The experimental data are explained by the Kondo scattering in the presence of the crystal field splitting and various shapes of S(T) are related to different Kondo scales that characterize Ce and Yb ions at different temperatures. The low- and high-temperature behaviors are calculated for different fixed point models and the overall shape of S(T) is obtained by interpolation. At high temperatures, we use the Coqblin-Schrieffer model and calculate S(T) by perturbation expansion with renormalized coupling constants. The renormalization is performed by the 'poor man's scaling'. At low temperatures, we describe the dilute Ce and Yb alloys by an effective spin-degenerate single-impurity Anderson model, and the stoichiometric compounds by an effective spin-degenerate periodic Anderson model. The parameters of these low-temperature models are such that their effective Kondo scale coincides with the lowest Kondo scale of the Coqblin-Schrieffer model. The interpolation between the results obtained for the Anderson model and the Coqblin-Schrieffer model explains the overall thermoelectric properties of most Ce and Yb intermetallics.

cond-mat.str-el↗

arXiv2001

Theory of valence transitions in Ytterbium and Europium intermetallics

The exact solution of the multi-component Falicov-Kimball model in infinite-dimensions is presented and used to discuss a new fixed point of valence fluctuating intermetallics with Yb and Eu ions. In these compounds, temperature, external magnetic field, pressure, or chemical pressure induce a transition between a metallic state with the f-ions in a mixed-valent (non-magnetic) configuration and a semi-metallic state with the f-ions in an integral-valence (paramagnetic) configuration. The zero-field transition occurs at the temperature Tv, while the zero-temperature transition sets in at the critical field Hc. We present the thermodynamic and dynamic properties of the model for an arbitrary concentration of d- and f-electrons. For large U, we find a MI transition, triggered by the temperature or field-induced change in the f-occupancy.

cond-mat.str-el↗

arXiv2001

Thermal transport in the Falicov-Kimball model

We prove the Jonson-Mahan theorem for the thermopower of the Falicov-Kimball model by solving explicitly for the correlation functions in the large dimensional limit. We prove a similar result for the thermal conductivity. We separate the results for thermal transport into the pieces of the heat current that arise from the kinetic energy and those that arise from the potential energy. Our method of proof is specific to the Falicov-Kimball model, but illustrates the near cancellations between the kinetic-energy and potential-energy pieces of the heat current implied by the Jonson-Mahan theorem.

cond-mat.str-el↗

arXiv2001

Kondo effect in Ce(x)La(1-x)Cu(2.05)Si(2) intermetallics

The magnetic susceptibility and susceptibility anisotropy of the quasi-binary alloy system Ce(x)La(1-x)Cu(2.05)Si(2) have been studied for low concentration of Ce ions. The single-ion desc ription is found to be valid for x < 0.1. The experimental results are discussed in terms of t he degenerate Coqblin-Schrieffer model with a crystalline electric field splitting Delta = 330 K. The properties of the model, obtained by combining the lowest-order scaling and the pertur bation theory, provide a satisfactory description of the experimental data down to 30 K. The e xperimental results between 20 K and 2 K are explained by the exact solution of the Kondo mode l for an effective doublet.

cond-mat.str-el↗

arXiv2001

Exact solution of the multi-component Falicov-Kimball model in infinite dimensions

The exact solution for the thermodynamic and dynamic properties of the infinite-dimensional multi-component Falicov-Kimball model for arbitrary concentration of d- and f-electrons is presented. The emphasis is on a descriptive derivation of important physical quantities by the equation of motion technique. We provide a thorough discussion of the f-electron Green function and of the susceptibility to spontaneous hybridization. The solutions are used to illustrate different physical systems ranging from the high-temperature phase of the YbInCu4 family of materials to an examination of classical intermediate valence systems that can develop a spontaneous hybridization at T=0.

cond-mat.str-el↗

arXiv2000

Perturbation expansion for 2-D Hubbard model

We develop an efficient method to calculate the third-order corrections to the self-energy of the hole-doped two-dimensional Hubbard model in space-time representation. Using the Dyson equation we evaluate the renormalized spectral function in various parts of the Brillouin zone and find significant modifications with respect to the second-order theory even for rather small values of the coupling constant U. The spectral function becomes unphysical for $ U \simeq W $, where W is the half-width of the conduction band. Close to the Fermi surface and for U<W, the single-particle spectral weight is reduced in a finite energy interval around the Fermi energy. The increase of U opens a gap between the occupied and unoccupied parts of the spectral function.

cond-mat.str-el↗

arXiv1999

Approximate scaling relation for the anharmonic electron-phonon problem

An approximate scaling relation is found for the transition temperature to a charge-density-wave instability in the anharmonic electron-phonon problem, which maps a wide range of interaction strengths, anharmonicities, and phonon frequencies onto a common functional form. The relation employs the wave-function renormalization parameter and is valid even for systems that are not Fermi liquids.

cond-mat.supr-con↗

arXiv1996

Anomalous magnetic response of the valence-fluctuating compound YbInCu4

The exact solution of the spin one-half Falicov-Kimball model, with random hopping between the lattice sites, is used to explain the anomalous magnetic response of Yb-based valence-fluctuating intermetallic compounds. The anomalous behavior arises from an entropy-driven local-moment--nonmagnetic transition of unhybridized Yb ions in these materials which can also be used to explain the observed metamagnetism and resistivity anomalies.

cond-mat↗

arXiv1993

Transport Coefficients of the Anderson Model via the Numerical Renormalization Group

The transport coefficients of the Anderson model are calculated by extending Wilson's NRG method to finite temperature Green's functions. Accurate results for the frequency and temperature dependence of the single--particle spectral densities and transport time $τ(ω,T)$ are obtained and used to extract the temperature dependence of the transport coefficients in the strong correlation limit. The low temperature anomalies in the resistivity, $ρ(T)$, thermopower, $S(T)$, thermal conductivity $κ(T)$ and Hall coefficient, $R_{H}(T)$, are discussed. All quantities exhibit the expected Fermi liquid behaviour at low temperature with power law dependecies on $T/T_{K}$ in very good agreement with analytic results based on Fermi liquid theory. Scattering of conduction electrons in higher, $l>0$, angular momentum channels is also considered and an expression is derived for the corresponding transport time and used to discuss the influence of non--resonant scattering on the transport properties.

cond-mat↗