Searcharxiv⌕ Search

arXiv subjects

J. K. Freericks

Publications and source records attributed to J. K. Freericks.

At least 163 records · Page 9Linked to original sources
arXiv2004

Strongly correlated multilayered nanostructures near the Mott transition

We examine devices constructed out of multilayered sandwiches of semi-infinite metal--barrier--semi-infinite metal, with the barrier tuned to lie near the quantum critical point of the Mott metal-insulator transition. By employing dynamical mean field theory, we are able to solve the many-body problem exactly (within the local approximation) and determine the density of states through the nanostructure and the charge transport perpendicular to the planes. We introduce a generalization of the Thouless energy that describes the crossover from tunneling to incoherent thermally activated transport.

cond-mat.str-el↗
arXiv2004

Dynamical mean field theory for strongly correlated inhomogeneous multilayered nanostructures

Dynamical mean field theory is employed to calculate the properties of multilayered inhomogeneous devices composed of semi-infinite metallic lead layers coupled via barrier planes that are made from a strongly correlated material (and can be tuned through the metal-insulator Mott transition). We find that the Friedel oscillations in the metallic leads are immediately frozen in and don't change as the thickness of the barrier increases from one to eighty planes. We also identify a generalization of the Thouless energy that describes the crossover from tunneling to incoherent Ohmic transport in the insulating barrier. We qualitatively compare the results of these self-consistent many-body calculations with the assumptions of non-self-consistent Landauer-based approaches to shed light on when such approaches are likely to yield good results for the transport.

cond-mat.str-el↗
arXiv2004

Parallelizing the Keldysh formalism for strongly correlated electrons

Nonequilibrium quantum mechanics can be solved with the Keldysh formalism, which evolves the quantum mechanical states forward in time in the presence of a time-dependent field, and then evolves them backward in time, undoing the effect of the time-dependent field. The Feynman path integral over the Keldysh contour is employed to calculate the strongly correlated Green's function. We examine the accuracy of this procedure for the simplest problem that requires a nonequilibrium formulation: the f-electron spectral function of the spinless Falicov-Kimball model.

cond-mat.str-el↗
arXiv2004

F-electron spectral function near a quantum critical point

We calculate the f-electron spectral function using a Keldysh formalism for the Falicov-Kimball model in infinite dimensions. We study the region close to the quantum critical point on both the hypercubic and Bethe lattices.

cond-mat.str-el↗
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↗
arXiv2004

Resonant Enhancement of Electronic Raman Scattering

We present an exact solution for electronic Raman scattering in a single-band, strongly correlated material, including nonresonant, resonant and mixed contributions. Results are derived for the spinless Falicov-Kimball model, employing dynamical mean field theory; this system can be tuned through a Mott metal-insulator transition.

cond-mat.str-el↗
arXiv2004

Effect of Particle-Hole Asymmetry on the Mott-Hubbard Metal-Insulator Transition

The Mott-Hubbard metal-insulator transition is one of the most important problems in correlated electron systems. In the past decade, much progress has been made on examining a particle-hole symmetric form of the transition in the Hubbard model with dynamical mean field theory where it was found that the electronic self energy develops a pole at the transition. We examine the particle-hole asymmetric metal-insulator transition in the Falicov-Kimball model, and find that a number of features change when the noninteracting density of states has a finite bandwidth. Since, generically particle-hole symmetry is broken in real materials, our results have an impact on understanding the metal-insulator transition in real materials.

cond-mat.str-el↗
arXiv2004

Crossover from tunneling to incoherent (bulk) transport in a correlated nanostructure

We calculate the junction resistance for a metal-barrier-metal device with the barrier tuned to lie just on the insulating side of the metal-insulator transition. We find that the crossover from tunneling behavior in thin barriers at low temperature to incoherent transport in thick barriers at higher temperature is governed by a generalized Thouless energy. The crossover temperature can be estimated from the low temperature resistance of the device and the bulk density of states of the barrier.

cond-mat.str-el↗
arXiv2003

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 $\textbf{q}=0$ (Raman) scattering and find that resonant effects can be quite large, and yield a triple 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.

cond-mat.str-el↗
arXiv2003

Thermal transport in the Falicov-Kimball model on a Bethe lattice

We calculate thermal transport in the Falicov-Kimball model on an infinite-coordination-number Bethe lattice. We perform numerical calculations of the thermoelectric characteristics and concentrate on finding materials parameters for which the electronic thermoelectric figure-of-merit ZT is large, suggesting potential cooling and power generation applications. Surprisingly, the Bethe lattice has significant qualitative and quantitative differences with the previously studied hypercubic lattice. At low temperature it is unlikely that these systems can be employed in thermoelectric devices due to the low conductivities and due to a larger lattice contribution to the thermal conductivity $κ_L$, but at high temperature, the thermoelectric parameters appear more promising for devices due to a significant enhancement of ZT and a smaller relative contribution by the lattice thermal conductivity.

cond-mat.str-el↗
arXiv2003

Charge stripes due to electron correlations in the two-dimensional spinless Falicov-Kimball model

We calculate the restricted phase diagram for the Falicov-Kimball model on a two-dimensional square lattice. We consider the limit where the conduction electron density is equal to the localized electron density, which is the limit related to the S_z=0 states of the Hubbard model. After considering over 20,000 different candidate phases (with a unit cell of 16 sites or less) and their thermodynamic mixtures, we find only about 100 stable phases in the ground-state phase diagram. We analyze these phases to describe where stripe phases occur and relate these discoveries to the physics behind stripe formation in the Hubbard model.

cond-mat.str-el↗
arXiv2003

Charge-density-wave order parameter of the Falicov-Kimball model in infinite dimensions

In the large-U limit, the Falicov-Kimball model maps onto an effective Ising model, with an order parameter described by a BCS-like mean-field theory in infinite dimensions. In the small-U limit, van Dongen and Vollhardt showed that the order parameter assumes a strange non-BCS-like shape with a sharp reduction near T approx T_c/2. Here we numerically investigate the crossover between these two regimes and qualitatively determine the order parameter for a variety of different values of U. We find the overall behavior of the order parameter as a function of temperature to be quite anomalous.

cond-mat.str-el↗
arXiv2003

Inelastic x-ray scattering as a probe of electronic correlations

We construct an exact dynamical mean field theory for nonresonant inelastic light scattering in the infinite-dimensional Falicov-Kimball model, which can be tuned through a quantum critical metal-insulator transition. Due to the projection of the polarization orientations onto different regions of the Brillouin zone and due to the transfer of energy and momentum from the light to the strongly correlated charge excitations, the nature of the dynamics can be naturally interpreted as strongly temperature-dependent low-energy particle-hole excitations and weakly temperature-dependent high-energy charge transfer excitations which depend delicately on the electronic correlations. These results can be used to give important information concerning the evolution of charge dynamics in different regions of the Brillouin zone.

cond-mat.str-el↗
arXiv2003

Mesoscopics in Spintronics: Quantum Interference Effects in Spin-Polarized Electron Transport

We generalize a Landauer-type formula, using a real$\otimes$spin-space Green function technique, to treat spin-dependent transport in quantum-coherent conductors attached to two ferromagnetic contacts. The formalism is employed to study the properties of components of an exact zero-temperature conductance matrix ${\bf G}$, as well as their mesoscopic fluctuations, describing injection and detection of a spin-polarized current in a two-dimensional system where electrons exhibit an interplay between Rashba spin-orbit (SO) coupling and phase-coherent propagation through a disordered medium. Strong Rashba coupling leads to a dramatic reduction of localization effects on the conductances and their fluctuations, whose features depend on the spin-polarization of injected electrons. In the limit of weak Rashba interaction antilocalization vanishes (i.e., the sum of the matrix elements of ${\bf G}$ is almost independent of the SO coupling), but the partial spin-resolved conductances can still be non-zero. Besides spin-resolved conductance fluctuations and antilocalization, unusual quantum interference effects are revealed in this system leading to a negative difference between the partial conductances for a parallel and an antiparallel orientation of the contact magnetization, in a range of disorder strengths and for a particular spin-polarization of incoming electron with respect to the direction of Rashba electric field.

cond-mat.mes-hall↗
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

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 formulae are numerically equal to each other; an explicit derivation showing this equivalence is presented here.

cond-mat.str-el↗
arXiv2002

Nonresonant inelastic light scattering in the Hubbard model

Inelastic light scattering from electrons is a symmetry-selective probe of the charge dynamics within correlated materials. Many measurements have been made on correlated insulators, and recent exact solutions in large dimensions explain a number of anomalous features found in experiments. Here we focus on the correlated metal, as described by the Hubbard model away from half filling. We can determine the B1g Raman response and the inelastic X-ray scattering along the Brillouin zone diagonal exactly in the large dimensional limit. We find a number of interesting features in the light scattering response which should be able to be seen in correlated metals such as the heavy fermions.

cond-mat.str-el↗