Embedding approach for dynamical mean field theory of strongly correlated heterostructures

We present an embedding approach based on localized basis functions which permits an efficient application of the dynamical mean field theory (DMFT) to inhomogeneous correlated materials, such as semi-infinite surfaces and heterostructures. In this scheme, the semi-infinite substrate leads connected to both sides of the central region of interest are represented via complex, energy-dependent embedding potentials that incorporate one-electron as well as many-body effects within the substrates. As a result, the number of layers which must be treated explicitly in the layer-coupled DMFT equation is greatly reduced. To illustrate the usefulness of this approach, we present numerical results for strongly correlated surfaces, interfaces, and heterostructures of the single-band Hubbard model.Comment: 8 pages, 4 figures; typos correcte

Pressure-induced metal-insulator transition in LaMnO3 is not of Mott-Hubbard type

Calculations employing the local density approximation combined with static and dynamical mean-field theories (LDA+U and LDA+DMFT) indicate that the metal-insulator transition observed at 32 GPa in paramagnetic LaMnO3 at room temperature is not a Mott-Hubbard transition, but is caused by orbital splitting of the majority-spin eg bands. For LaMnO3 to be insulating at pressures below 32 GPa, both on-site Coulomb repulsion and Jahn-Teller distortion are needed.Comment: 4 pages, 3 figure

Projective Quantum Monte Carlo Method for the Anderson Impurity Model and its Application to Dynamical Mean Field Theory

We develop a projective quantum Monte Carlo algorithm of the Hirsch-Fye type for obtaining ground state properties of the Anderson impurity model. This method is employed to solve the self-consistency equations of dynamical mean field theory. It is shown that the approach converges rapidly to the ground state so that reliable zero-temperature results are obtained. As a first application, we study the Mott-Hubbard metal-insulator transition of the one-band Hubbard model, reconfirming the numerical renormalization group results.Comment: 4 pages, 4 figure

In-plane gate single-electron transistor in Ga[Al]As fabricated by scanning probe lithography

A single-electron transistor has been realized in a Ga[Al]As heterostructure by oxidizing lines in the GaAs cap layer with an atomic force microscope. The oxide lines define the boundaries of the quantum dot, the in-plane gate electrodes, and the contacts of the dot to source and drain. Both the number of electrons in the dot as well as its coupling to the leads can be tuned with an additional, homogeneous top gate electrode. Pronounced Coulomb blockade oscillations are observed as a function of voltages applied to different gates. We find that, for positive top-gate voltages, the lithographic pattern is transferred with high accuracy to the electron gas. Furthermore, the dot shape does not change significantly when in-plane voltages are tuned.Comment: 4 pages, 3 figure

The Use of Function in Infant Concept Acquisition

The use of function for concept formation in 5 and 8 month old infants was studied in an experiment employing a conceptual adaptation of the standard habituation paradigm. A total of 64 male and female infants were shown videoptaped presentations which involved changes in form and functional attributes of selected stimuli. The stimuli consisted of striped figures which could vary in form (shmoo-shaped or H-shaped) and function (side-to-side movements or up-down movements). During habituation, all infants were shown multiexemplars of a specific figure performing a single movement pattern; the figures varied only in color. During test trials, the infants were shown (1) a change only in form, (2) a change only in movement, (3) a change in movement contrasted with a change in form, or (4) a change in movement contrasted with a combined movement/form change. Total visual fixation times to the various changes in stimuli presented during test trials were compared. The results provide partial, but not conclusive, support for the hypothesis that function serves as the central core for concept acquisition in infancy at both 5 and 8 months of age. The results do not, however, point to a developmental age trend towards either increased or decreased use of functional attributes for concept acquisition

Two Aspects of the Mott-Hubbard Transition in Cr-doped V_2O_3

The combination of bandstructure theory in the local density approximation with dynamical mean field theory was recently successfully applied to V$_2$O$_3$ -- a material which undergoes the f amous Mott-Hubbard metal-insulator transition upon Cr doping. The aim of this sh ort paper is to emphasize two aspects of our recent results: (i) the filling of the Mott-Hubbard gap with increasing temperature, and (ii) the peculiarities of the Mott-Hubbard transition in this system which is not characterized by a diver gence of the effective mass for the $a_{1g}$-orbital.Comment: 2 pages, 3 figures, SCES'04 conference proceeding