Ann. Phys. (Berlin) 523, No. 8 – 9, 583 – 588 (2011) / DOI 10.1002/andp.201152308 CONTENTS Full text on our homepage at www.ann-phys.org Special Topic Issue Electronic Correlations in Models and Materials Guest Editors: Peter van Dongen, Marcus Kollar, and Thomas Pruschke PREFACE Page 589 – 590 P. van Dongen, M. Kollar, and T. Pruschke ORIGINAL ARTICLES Page 591 – 598 P. Wölfle and E. Abrahams Quantum critical behavior of heavy fermions: Quasiparticles in the Gaussian fluctuation regime Landau quasiparticle (qp) theory may be extended into the non-Fermi liquid regime of metallic compounds near a quantum critical point (QCP), provided the width of the quasiparticle states is less than their energy. Sufficiently far from the QCP, when the critical fluctuations are non-interacting, their influence on the qp properties may be calculated in a controlled way. Page 599 – 611 H. v. Löhneysen Electron-electron interactions and the metal-insulator transition in heavily doped silicon μ The metal-insulator (MI) transition in (c) N << NO Si:P can be tuned by varying the P concentration or – for barely insulating samples – by application of uniaxial μ N ~< NO stress S. On-site Coulomb interactions lead to the formation of localized magnetic moments and the Kondo effect on the metallic side, and to a Hubbard splitting of the donor band on the insulating side. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 584 Page 612 – 620 Contents P. Sun, M. Søndergaard, B. B. Iversen, and F. Steglich Strong electron correlations in FeSb2 FeSb2 has been recently identified as a new model system for studying manybody renormalizations in a d-electron based narrow gap semiconducting system, strongly resembling FeSi. The electron-electron correlations in FeSb2 manifest themselves in a wide variety of physical properties including electrical and thermal transport, optical conductivity, magnetic susceptibility, specific heat and so on. The authors review some of the properties that form a set of experimental evidences revealing a significant role of correlation effects in FeSb2 . Page 621 – 628 B. Obert, S. Takei, and W. Metzner Anomalous criticality near semimetal-to-superfluid quantum phase transition in a two-dimensional Dirac cone model The authors analyze the scaling behavior at and near a quantum critical point separating a semimetallic from a superfluid phase. To this end they compute the renormalization group flow for a model of attractively interacting electrons with a linear dispersion around a single Dirac point. They study both ground state and finite temperature properties. Page 629 – 637 M. Imada, Y. Yamaji, S. Sakai, and Y. Motome Theory of pseudogap and superconductivity in doped Mott insulators Underdoped Mott insulators provide us with a cofermion challenge of many-body physics. Recent renewed understanding is discussed in terms of the evolution of pole and zero structure of the singleparticle Green’s function. Pseudogap as well quasiparticle as Fermi arc/pocket structure in the underdoped cuprates is well reproduced from the recent cluster extension of the dynamical mean-field theory. Emergent coexisting zeros and poles set the underdoped Mott insulator apart from the Fermi liquid, separated by topological transitions. The cofermion proposed as a generalization of exciton in the slave-boson framework accounts for the origin of the zero surface formation. The cofermion-quasiparticle hybridization gap offers a natural understanding of the pseudogap and various unusual Mottness. Furthermore the cofermion offers a novel pairing mechanism, where the cofermion has two roles: It reinforces the Cooper pair as a pair partner of the quasiparticle and acts as a glue as well. It provides a strong insight for solving the puzzle found in the dichotomy of the gap structure. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.ann-phys.org Ann. Phys. (Berlin) 523, No. 8 – 9 (2011) Page 638 – 644 585 W. Hanke, Ch. Platt, and R. Thomale Order-parameter anisotropies in the pnictides: An optimization principle for multi-band superconductivity ky/π Using general arguments of an optimization tak61 59 63 57 ing place between the pair wave function and the 1 49 55 repulsive part of the electron-electron interaction, 51 53 the authors analyze the superconducting gap in 45 43 29 27 47 materials with multiple Fermi-surface (FS) pock31 13 41 25 9 0 17 1 33 ets, with exemplary application to two proto-type 5 23 39 19 21 35 37 ferropnictide setups. The main point is to show 0 1 that the SC state, its gap, and, in particular, its kx/π anisotropy in momentum space is determined by an optimization which determines and optimizes the interplay between the attractive interaction in the SC-channel and the Coulomb repulsion. Page 645 – 651 J. Deisenhofer, M. Schmidt, Z. Wang, Ch. Kant, F. Mayr, F. Schrettle, H.-A. Krug von Nidda, P. Ghigna, V. Tsurkan, and A. Loidl Lattice vibrations in KCuF3 Page 652 – 663 7.5 (a) -4 H = 1T KCuF3 7.0 χ (10 emu/mol) The authors report on polarization dependent reflectivity measurements in KCuF3 in the far-infrared frequency regime. The observed IR active phonons at room temperature are in agreement with the expected modes for tetragonal symmetry. A splitting of one mode already at 150 K and the appearance of a new mode in the vicinity of the Néel temperature is observed. TN= 40K 6.5 6.0 5.5 5.0 0 100 200 300 T (K) 400 V. Moshnyaga and K. Samwer Electron-lattice correlations and phase transitions in CMR manganites www.ann-phys.org 10000 10 8000 н Ͳ Ͳ н 6000 8 6 4000 4 2000 2 0 R3ω (Ω) CMR (7T), % Interrelations between global and local structure and magnetism and transport in three-dimensional perovskite manganites is reviewed and compared with recent studies on thin films and superlattices. The concept of correlated JahnTeller polarons is discussed within the phase separation scenario; their role in the local and global structural modifications of manganites is demonstrated. 0 0 50 100 150 200 250 300 350 T (K) © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 586 Page 664 – 671 Contents S. Kirino and K. Ueda Nonlinear transport through quantum dots studied by the time-dependent DMRG Recent developments on studies of transport through quantum dots obtained by applying the time-dependent density matrix renormalization group method are summarized. Some new aspects of Kondo physics which appear in nonequilibrium steady states are discussed both for the single dot case and for the serially coupled double-quantum-dot case. Page 672 – 681 A. Georges Thinking locally: Reflections on Dynamical Mean-Field Theory from a high-temperature/high-energy perspective When spatial correlations are short-range, the physics of strongly correlated systems is controlled by local quantum fluctuations. In those regimes, Dynamical Mean-Field Theory can be viewed as a ‘compass’ which provides guidance on the relevant degrees of freedom and their effective dynamics over intermediate energy scales. These intermediate energy scales and associated crossovers play a crucial role in the physics of strongly correlated materials. Page 682 – 688 J. Kuneš and V. I. Anisimov The authors review their investigations of electronic properties of strongly correlated materials using the combination of first principles electronic band structures and the dynamical mean-field theory, so called LDA+DMFT method. Their investigations focus on two phenomena, the spin state transitions and their relationship to the metalinsulator transition, and the effect of hybridization between correlated and ligand orbitals in chargetransfer type materials. Page 689 – 697 Spectral density Various scenarios of metal-insulator transition in strongly correlated materials O-p eg- π a1g eg- σ v=1.0 v=0.85 v=0.8 -10 -5 0 5 Energy (eV) H. Lee, Y.-Z. Zhang, H. O. Jeschke, and R. Valentí Anisotropic two-orbital Hubbard model: Single-site versus cluster dynamical mean-field theory The anisotropic two-orbital Hubbard model with different bandwidths and degrees of frustration in each orbital is investigated in the framework of both single-site dynamical mean-field theory (DMFT) as well as its cluster extension (DCA) for clusters up to four sites combined with a continuous-time quantum Monte Carlo algorithm. This model shows a rich phase diagram which includes the appearance of orbital selective phase transitions, nonFermi liquid behavior as well as antiferromagnetic metallic states. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.ann-phys.org Ann. Phys. (Berlin) 523, No. 8 – 9 (2011) Page 698 – 705 587 A. Toschi, G. Rohringer, A. A. Katanin, and K. Held Ab initio calculations with the dynamical vertex approximation The authors propose an approach for the ab initio calculation of materials i j with strong electronic correlations W V which is based on all local (fully irrei j i j i i' j' j + = ducible) vertex corrections beyond the bare Coulomb interaction. It includes the so-called GW and dynamical mean field theory and important non-local correlations beyond, with a computational effort estimated to be still manageable. eff ij Page 706 – 714 ij Ch. Jung, A. Wilhelm, H. Hafermann, S. Brener, and A. Lichtenstein Superperturbation theory on the real-axis In this article the authors formulate the superperturbation theory for the Anderson impurity model on the real axis. The resulting impurity solver allows to evaluate dynamical quantities without numerical analytical continuation by the maximum entropy method or Padé approximants. Page 715 – 723 V. Janiš and V. Pokorný Renormalized perturbation theories of Anderson localization: Self-consistent two-particle vertices The effects of quantum coherence on two-particle vertex functions due to impurity scattering of electrons are studied. The authors use the diagrammatic perturbation expansion in the impurity potential and analyze possible ways how to introduce renormalizations on the two-particle level. Page 724 – 731 D. Baeriswyl Adiabatic continuity and broken symmetry in many-electron systems: A variational perspective Variational wave functions are very useful for describing the panoply of ground states found in interacting many-electron systems. Some particular trial states are “adiabatically” linked to a reference state, from which they borrow the essential properties. A prominent example is the Gutzwiller ansatz, where one starts with the filled Fermi sea. To describe symmetry breaking, the reference state has to be modified accordingly. www.ann-phys.org © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 588 Contents Page 732 – 740 D. Müller, S. Pilgram, T. M. Rice, and M. Sigrist Extending the Gutzwiller approximation for liquid 3 He by including intersite correlations Page 741 – 750 0 Gutzwiller approximation Bond approximation 1/D approximation Ekin The simple Gutzwiller approximation, applied to the approach to Mott localization in a half-filled band Hubbard model, gives a remarkably good description of the properties of liquid 3 He as the liquid-solid transition is approached under pressure. Here the Gutzwiller approximation is extended to incorporate correlations between nearest neighbors. -0.5 -1 0 0.1 0.2 n 0.3 0.4 0.5 R. Trencsényi, K. Gulácsi, E. Kovács, and Z. Gulácsi Exact ground states for polyphenylene type of hexagon chains CH 3 A technique based on positive semidefinite operator properties has been used a) O ..... in deducing exact ground states for CH3 hexagon chains of polyphenylene type (hexagons interconnected by bonds b) ..... build up the 1D periodic structure), S placed in a constant external magnetic field perpendicular to the surface containing the system. Page 751 – 758 CH3 CH3 O S O ..... CH3 CH3 ..... S R. Shankar The last word in strong correlations In the Fractional Quantum Hall Effect (FQHE), in the noninteracting limit, only a fraction ν of the Lowest Landau Level (LLL) is occupied, producing a huge degeneracy. Interactions lift this degeneracy and mix in higher LL’s. In the limit in which we ignore all but the LLL, the kinetic energy is an irrelevant constant and the ratio of potential to kinetic energy is essentially infinite, making this the most strongly correlated problem imaginable. The Hamiltonian theory of the FQHE deals with this problem with some success. Annalen der Physik is indexed in Chemical Abstracts Service/SciFinder, COMPENDEX, Current Contents®/Physical, Chemical & Earth Sciences, FIZ Karlsruhe Databases, INIS: International Nuclear Information System Database, INSPEC, Journal Citation Reports/Science Edition, Science Citation Index Expanded™, Science Citation Index® , SCOPUS, Statistical Theory & Method Abstracts, VINITI, Web of Science® , Zentralblatt MATH/Mathematics Abstracts Recognized by the European Physical Society © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.ann-phys.org

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