A. M. Shvaika

Dynamical susceptibilities in a strong coupling approach

A general scheme to calculate dynamical susceptibilities of strongly correlated electron systems within the dynamical mean field theory is developed. The approach is based on an expansion over electron hopping around the atomic limit (within the diagrammatic technique for site operators: projection and Hubbard ones) in infinite dimensions. As an example, the Falicov-Kimball and simplified pseudospin-electron models are considered and analytical expressions for the dynamical susceptibilities are obtained.

Optical and dc-transport properties of a strongly correlated charge-density-wave system : Exact solution in the ordered phase of the spinless Falicov-Kimball model with dynamical mean-field theory

We derive the dynamical mean-field theory equations for transport in an ordered charge-densitywave phase on a bipartite lattice. The formalism is applied to the spinless Falicov-Kimball model on a hypercubic lattice at half filling. We determine the many-body density of states, the dc charge and heat conductivities, and the optical conductivity. Vertex corrections continue to vanish within the ordered phase, but the density of states and the transport coefficients show anomalous behavior due to the rapid development of thermally activated subgap states. We also examine the optical sum rule and sum rules for the first three moments of the Green’s functions within the ordered phase and see that the total optical spectral weight in the ordered phase either decreases or increases depending on the strength of the interactions.

Directly characterizing the relative strength and momentum dependence of electron-phonon coupling using resonant inelastic x-ray scattering

T. P. Devereaux,1, 2 A. M. Shvaika,3 K. Wu,1 K. Wohlfeld,4 C. J. Jia,1 Y. Wang,1 B. Moritz,1 L. Chaix,1 W.-S. Lee,1 Z.-X. Shen,1, 2, 5 G. Ghiringhelli,6 and L. Braicovich6 Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025. Geballe Laboratory for Advanced Materials, Stanford University, CA 94305. Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, Lviv, 79011 Ukraine. Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, Pasteura 5, PL-02093 Warsaw, Poland Dept. of Physics and Applied Physics, Stanford University, CA 94305. CNR-SPIN and Dipartimento di Fisica, Politecnico di Milano, I-20133 Milano, Italy. (Dated: May 11, 2016)

On the electron spectrum of the Hubbard model including interactions with local anharmonic vibrations

Abstract This paper presents a self-consistent calculation of the single-electron excitation spectrum within the framework of an Hubbard model including interaction with pseudospin degrees of freedom due to the anharmonic vibrations of the apex oxygen (O(4)) in high-temperature superconductors of the YBaCuO-type (Muller model). The spectra are calculated for different electron concentrations using Greens function equations with a decoupling analogous to a Hubbard-I approximation. We use an approach which is based on the exact solution of the single-site problem. In contrast to the Hubbard model, the spectra show additional subbands due to the interaction of the electrons with the anharmonic vibrations (pseudospins). Those interactions result in the destruction of the electron-hole symmetry and the system can show hole conductivity even at half filling.

Time-domain pumping a quantum-critical charge density wave ordered material

We determine the exact time-resolved photoemission spectroscopy for a nesting driven charge density wave (described by the spinless Falicov-Kimball model within dynamical mean-field theory). The pump-probe experiment involves two light pulses: the first is an ultrashort intense pump pulse that excites the system into nonequilibrium, and the second is a lower amplitude, higher frequency probe pulse that photoexcites electrons. We examine three different cases: the strongly correlated metal, the quantum-critical charge density wave, and the critical Mott insulator. Our results show that the quantum critical charge density wave has an ultraefficient relaxation channel that allows electrons to be de-excited during the pump pulse, resulting in little net excitation. In contrast, the metal and the Mott insulator show excitations that are closer to what one expects from these systems. In addition, the pump field produces spectral band narrowing, peak sharpening, and a spectral gap reduction, all of which rapidly return to their field free values after the pump is over.

Electronic Raman scattering in correlated materials: A treatment of nonresonant, mixed, and resonant scattering using dynamical mean-field theory

We solve for the electronic Raman scattering response functions on an infinite-dimensional hypercubic lattice employing dynamical mean field theory. This contribution extends previous work on the nonresonant response to include the mixed and resonant contributions. We focus our attention on the spinless Falicov-Kimball model, where the problem can be solved exactly, and the system can be tuned to go through a Mott-Hubbard-like metal-insulator transition. Resonant effects vary in different scattering geometries, corresponding to the symmetries of the charge excitations scattered by the light. We do find that the Raman response is large near the double resonance, where the transfered frequency is close to the incident photon frequency. We also find a joint resonance of both the charge-transfer peak and the low-energy peak when the incident photon frequency is on the order of the interaction strength. In general, the resonance effects can create order of magnitude (or more) enhancements of features in the nonresonant response, especially when the incident photon frequency is somewhat larger than the frequency of the nonresonant feature. Finally, we find that the resonant effects also exhibit isosbestic behavior, even in the A1g and B2g sectors, and it is most prominent when the incident photon frequency is on the order of the interaction energy.

Equivalence of the Falicov-Kimball and Brandt-Mielsch forms for the free energy of the infinite-dimensional Falicov-Kimball model

Falicov and Kimball proposed a real-axis form for the free energy of the Falicov-Kimball model that was modified for the coherent potential approximation by Plischke. Brandt and Mielsch proposed an imaginary-axis form for the free energy of the dynamical mean field theory solution of the Falicov-Kimball model. It has long been known that these two formulas are numerically equal to each other; an explicit derivation showing this equivalence is presented here.

Electronic thermal transport in strongly correlated multilayered nanostructures

The formalism for a linear-response many-body treatment of the electronic contributions to thermal transport is developed for multilayered nanostructures. By properly determining the local heat-current operator, it is possible to show that the Jonson-Mahan theorem for the bulk can be extended to inhomogeneous problems, so the various thermal-transport coefficient integrands are related by powers of frequency (including all effects of vertex corrections when appropriate). We illustrate how to use this formalism by showing how it applies to measurements of the Peltier effect, the Seebeck effect, and the thermal conductance.

Resonant enhancement of inelastic light scattering in strongly correlated materials

We use dynamical mean field theory to find an exact solution for inelastic light scattering in strongly correlated materials such as those near a quantum-critical metal-insulator transition. We evaluate the results for q=0 (Raman) scattering and find that resonant effects can be quite large, and yield a double resonance, a significant enhancement of nonresonant scattering peaks, a joint resonance of both peaks when the incident photon frequency is on the order of U, and the appearance of an isosbestic point in all symmetry channels for an intermediate range of incident photon frequencies.

Theoretical description of pump/probe experiments in electron-mediated charge-density-wave insulators

In this review, we develop the formalism employed to describe charge-density-wave insulators in pump/probe experiments using ultra short driving pulses of light. The theory emphasizes exact results in the simplest model for a charge-density wave insulator (given by a noninteracting systems with two bands and a gap) and by employing nonequilibrium dynamical mean-field theory to solve the Falicov-Kimball model in its ordered phase. We show both how to develop the formalism and how the solutions behave. Care is taken to describe the details behind these calculations and to show how to verify their accuracy via sum-rule constraints.