Th. Pruschke

Anomalous normal-state properties of high-Tc superconductors : intrinsic properties of strongly correlated electron systems ?

Abstract A systematic study of optical and transport properties of the Hubbard model, based on the Metzner-Vollhardt dynamical mean-field approximation, is reviewed. This model shows interesting anomalous properties that are, in our opinion, ubiquitous to single-band strongly correlated systems (for all spatial dimensions greater than one) and also compare qualitatively with many anomalous transport features of the high-T c cuprates. This anomalous behaviour of the normal-state properties is traced to a ‘collective single-band Kondo effect’, in which a quasiparticle resonance forms at the Fermi level as the temperature is lowered, ultimately yielding a strongly renormalized Fermi liquid at zero temperature.

Hubbard model at infinite dimensions: Thermodynamic and transport properties

We present results on the thermodynamic quantities, resistivity, and optical conductivity for the Hubbard model on a simple hypercubic lattice in infinite dimensions. Our results for the paramagnetic phase display the features expected from an intuitive analysis of the one-particle spectra and substantiate the similarity of the physics of the Hubbard model to those heavy-fermion systems. The calculations were performed using an approximate solution to the single-impurity Anderson model, wich is the key quantity entering the solution of the Hubbard model in this limit

Numerical renormalization group calculations for the self-energy of the impurity Anderson model

We present a new method for calculating directly the one-particle self-energy of an impurity Anderson model with Wilsons numerical renormalization group method by writing this quantity as the ratio of two correlation functions. This way of calculating turns out to be considerably more reliable and accurate than that via the impurity Greens function alone. We give results for the self-energy for the case of a constant coupling between the impurity and the conduction band and the effective arising in the dynamical mean-field theory of the Hubbard model. The implications of the problem of the metal-insulator transition in the Hubbard model are also discussed.

Mutual Experimental and Theoretical Validation of Bulk Photoemission Spectra of Sr1 xCaxVO3

We report high-resolution high-energy photoemission spectra together with parameter-free LDA + DMFT (local density approximation + dynamical mean-field theory) results for Sr1-xCaxVO3, a prototype 3d(1) system. In contrast to earlier investigations the bulk spectra are found to be insensitive to x. The good agreement between experiment and theory confirms the bulk sensitivity of the high-energy photoemission spectra.

Kinks in the dispersion of strongly correlated electrons

The properties of condensed matter are determined by single-particle and collective excitations and their mutual interactions. These quantum-mechanical excitations are characterized by an energy, E, and a momentum, ℏk, which are related through their dispersion, Ek. The coupling of excitations may lead to abrupt changes (kinks) in the slope of the dispersion. Kinks thus carry important information about the internal degrees of freedom of a many-body system and their effective interaction. Here, we report a novel, purely electronic mechanism leading to kinks, which is not related to any coupling of excitations. Namely, kinks are predicted for any strongly correlated metal whose spectral function shows a three-peak structure with well-separated Hubbard subbands and a central peak, as observed, for example, in transition-metal oxides. These kinks can appear at energies as high as a few hundred millielectron volts, as found in recent spectroscopy experiments on high-temperature superconductors1,2,3,4 and other transition-metal oxides5,6,7,8. Our theory determines not only the position of the kinks but also the range of validity of Fermi-liquid theory.

Theoretical Description of Time-Resolved Photoemission Spectroscopy: Application to Pump-Probe Experiments

The theory for time-resolved, pump-probe, photoemission spectroscopy and other pump-probe experiments is developed. The formal development is completely general, incorporating all of the nonequilibrium effects of the pump pulse and the finite time width of the probe pulse, and including possibilities for taking into account band structure and matrix element effects, surface states, and the interaction of the photoexcited electrons with the system leading to corrections to the sudden approximation. We also illustrate the effects of windowing that arise from the finite width of the probe pulse in a simple model system by assuming the quasiequilibrium approximation.

ELECTRONIC STRUCTURE OF THE HEAVY FERMION METAL LIV2O4

The electronic structure of the first reported heavy fermion compound without f-electrons LiV_2O_4 was studied by an ab-initio calculation method. In the result of the trigonal splitting and d-d Coulomb interaction one electron of the

Low-energy scale of the periodic Anderson model

d^{1.5}

Functional renormalization group for nonequilibrium quantum many-body problems

configuration of V ion is localized and the rest partially fills a relatively broad conduction band. The effective Anderson impurity model was solved by Non-Crossing-Approximation method, leading to an estimation for the single-site Kondo energy scale T_K. Then, we show how the so-called exhaustion phenomenon of Nozi\`eres for the Kondo lattice leads to a remarkable decrease of the heavy-fermion (or coherence) energy scale

A non-crossing approximation for the study of intersite correlations

T_{coh}\equiv {T_K}^2/D