Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session P11: Correlated Electrons: DMFT |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Randy Fishman, Oak Ridge National Laboratory Room: Colorado Convention Center Korbel 1F |
Wednesday, March 7, 2007 11:15AM - 11:27AM |
P11.00001: ABSTRACT WITHDRAWN |
Wednesday, March 7, 2007 11:27AM - 11:39AM |
P11.00002: An Extended Dynamical Cluster Approximation for Local-Moment Systems Karlis Mikelsons, Thomas Maier, Randy Fishman, Mark Jarrell We introduce an Extended Dynamical Cluster Approximation for studying local moment systems, such as Heisenberg and Ising models. Below $T_c$, self-consistency is imposed both for the order parameter and the correlation function. Exact enumeration and Monte-Carlo methods are used to solve the local moment problem on a cluster with coarse-grained effective interactions. Even if the original exchange interactions are short-ranged, the effective interactions are long-ranged. For a single site cluster this method is equivalent to the EDMFT. As the size of the cluster is increased, the fluctuations are systematically included into this approximation. We apply this method to the one-, two- and three-dimensional Ising models. We develop scaling analysis by increasing the cluster size to find the $T_c$. Unlike other expansions about the mean-field theory, our technique converges quite rapidly to the exact solutions, which are known analytically in one and two dimensions and to great accuracy from numerical work in three dimensions. Long- ranged interactions can easily be included in this method, i. e., for studying glassy systems. [Preview Abstract] |
Wednesday, March 7, 2007 11:39AM - 11:51AM |
P11.00003: Performance analysis of continuous-time solvers for quantum impurity models Emanuel Gull, Philipp Werner, Andrew Millis, Matthias Troyer Impurity solvers play an essential role in the numerical investigation of strongly correlated electrons systems within the ``dynamical mean field" approximation. Recently, a new class of continuous-time solvers has been developed, based on a diagrammatic expansion of the partition function in either the interactions or the impurity-bath hybridization. We investigate the performance of these two complimentary approaches and compare them to the well-established Hirsch-Fye method. The results show that the continuous-time methods, and in particular the version which expands in the hybridization, provide substantial gains in computational efficiency. [Preview Abstract] |
Wednesday, March 7, 2007 11:51AM - 12:03PM |
P11.00004: Efficient DMFT simulation of the Holstein-Hubbard model Philipp Werner, Andrew J. Millis We show that the hybridization expansion algorithm for quantum impurity models [PRL 97, 076405 (2006)] can easily handle a Holstein coupling to phonons. Our approach, which is based on the Lang-Firsov transformation, treats the phonons without approximations and does not affect the overall scaling of the algorithm. We apply the method to the Holstein-Hubbard model in the single site dynamical mean field approximation. [Preview Abstract] |
Wednesday, March 7, 2007 12:03PM - 12:15PM |
P11.00005: Dynamical vertex approximation --- a step beyond dynamical mean field theory Alessandro Toschi, Andrey Katanin, Karsten Held We have developed a new diagrammatic approach[1], coined ``Dynamical Vertex Approximation'' (D$\Gamma$A), with the aim of going beyond dynamical mean field theory for strongly correlated systems, by including the effects of long-range spatial correlations. Without resorting to any finite-size cluster scheme, D$\Gamma$A allows us to compute momentum dependent self-energies (and spectra), whose expressions are diagrammatically constructed starting from the two-particle irreducible local vertex. Therefore, D$\Gamma$A naturally applies for studying effects of magnetic fluctuations with large correlation length in strongly correlated systems, such as the Hubbard model. Specifically, we analyze the interplay between antiferromagnetic fluctuations and the Mott metal-insulator transition in three dimensions and the formation of a pseudogap in two dimensions. The diagrammatic nature of D$\Gamma$A, moreover, should allow for a generalization to the more realistic case of multi-band Hamiltonians. \newline [1] A. Toschi, A. Katanin, K. Held, cond-mat/0603100. [Preview Abstract] |
Wednesday, March 7, 2007 12:15PM - 12:27PM |
P11.00006: Optical Spectral Weight of the Hubbard Model -- Single-site DMFT Calculation and Comparison to Experimental Data Armin Comanac, Luca de' Medici, Massimo Capone, Andrew J. Millis The single-site dynamical mean field method is used to calculate the variation of optical spectral weight with doping, interaction strength and frequency for the one band Hubbard model. Upper Hubbard band, mid-infrared and coherent quasiparticle contributions are distinguished. It is argued that mid-infrared and coherent contributions can meaningfully be compared to experimental data on transition metal oxide materials such as high-temperature supercondutors. The comparison is used to estimate the strength of correlation effects in electron- and hole-doped superconductors. [Preview Abstract] |
Wednesday, March 7, 2007 12:27PM - 12:39PM |
P11.00007: Strong correlations on a triangular lattice: spectral weight suppression on the cobaltates. Dimitrios Galanakis, Tudor Stanescu, Philip Phillips Two experimental puzzles of strong correlations of the cobaltates (Na$_x$ CoO$_2$) are investigated. First the experimental claims that the optical conductivity displays a pseudogap feature. Second the suppression of spectral weight near the chemical potential in the removal spectrum of the x=0.3 material. We address this questions using the 2D Hubbard model in the triangular lattice in the framework of Cluster Dynamical Mean field theory (CDMFT). For x=0.3 we find a suppression of the spectral weight slightly above the chemical potential. The integrated optical conductivity displays no significant transfer of spectral weight from low to high energy as it would be indicative of a pseudogap. Comparison is made with single site, three site and four site clusters. [Preview Abstract] |
Wednesday, March 7, 2007 12:39PM - 12:51PM |
P11.00008: Analysis of the Dynamical Cluster Approximation for the Triangular Lattice Hubbard Model Christopher Varney, Richard Scalettar, Mark Jarrell, Alexandru Macridin, Brian Moritz The behavior of correlated electrons on triangular lattices is attracting increasing interest driven by experimental systems such as the cobaltates. To facilitate understanding of these correlations, we study the Hubbard model using Determinant Quantum Monte Carlo and the Dynamical Cluster Approximation. The spin, charge and pairing response functions obtained with the two methods are compared as a function of spatial lattice and cluster size, respectively, and the one particle spectrum is calculated. [Preview Abstract] |
Wednesday, March 7, 2007 12:51PM - 1:03PM |
P11.00009: NiO - Dynamical Mean Field Study of Charge-Transfer Insulator J. Kunes, V.I. Anisimov, A.V. Lukoyanov, D. Vollhardt Charge-transfer (CT) Mott insulators present an important group of transition metal compounds which exhibit phenomena such as metal-insulator transitions or high temperature superconductivity. The location of ligand states between the interaction-split $d$ bands leads to additional complexity, which requires a description beyond a simple Hubbard model. Using a combination of {\it ab initio} bandstructure and dynamical mean field theory we study the single particle spectrum of the prototypical CT insulator NiO. Including the O-$p$ orbitals to the Hamiltonian we obtain good agreement with PES and BIS experiments. Notably we find $d$-peak at the top of the valence band, which cannot be described in static theories, but which is seen in experiment and was reproduced in many-body calculations on small clusters. Studying the effect of doping we find the added holes to occupy the ligand $p$ orbitals despite large Ni-$d$ spectral weight at the top of the valence band. Heavy hole doping leads to a significant reconstruction of the single-particle spectrum and filling of the CT gap. This is the first LDA+DMFT study of charge transfer systems, which includes the $p-d$ hybridization explicitly and is thus able to provide a full description of valence and conduction band spectra. [Preview Abstract] |
Wednesday, March 7, 2007 1:03PM - 1:15PM |
P11.00010: Calculation of Magnetic Exchange Interactions in Mott-Hubbard Systems Quan Yin, Xiangang Yin, Sergey Savrasov An efficient method to magnetic exchange interactions in systems with strong electronic correlations is introduced. It is based on a magnetic force theorem which evaluates linear response due to rotations of magnetic moments and uses a novel spectral density functional framework combining our exact diagonalization based LDA+DMFT method. Applications on spin waves and magnetic transition temperatures of 3d transition metal oxides and 5f actinide oxides are in good agreement with experiments. [Preview Abstract] |
Wednesday, March 7, 2007 1:15PM - 1:27PM |
P11.00011: Combined LDA+Exact Diagonalization Study for Actinide Compounds Alexey Gordienko, Sergey Savrasov Exact diagonalization (ED) is a most straightforward and powerful way to study problems related to strong electron correlations, but very computationally demanding for $f$-electron systems. Computational efficiency of the ED approach can be greatly increased with help of iterative methods and we shall present our recent ED implementation which makes use of Kernel Polynomial Method (KPM) to calculate temperature Green's Function and self-energy. This allows us to deal relatively easy with problems whose size is 5$\cdot$10$^5$ states that is a characteristic for impurity problems with $f$-electrons. As an application, actinide compounds PuO$_2$ and UO$_2$, will be studied self-consistently using self- energies extracted from cluster ED and combined with electronic structure LDA calculation. [Preview Abstract] |
Wednesday, March 7, 2007 1:27PM - 1:39PM |
P11.00012: Non-collinear magnetism of GdB$_{4}$: A DFT+$U$ study M. N. Huda, Leonard Kleinman Lanthanide-borides show antiferromagnetic behavior where the magnetocrystalline anisotropy plays a major role in their magnetic structures. A recent neutron scattering experiment showed a particular noncollinear behavior of GdB$_{4}$ at room temperature. We will present our study on the non-collinear magnetism of GdB$_{4}$ with the GGA + $U$ method with spin orbit coupling. We have found that with or without spin-orbit coupling and with $U $collinear magnetism is favorable by few meV than the experimentally found noncollinear magnetic configuration. Among the noncollinear magnetism configurations that we have studied, when a $U $parameter and spin-orbit coupling are considered, the experimentally found noncollinear configuration was found to be favorable. However, the value of $U$ parameter is not unique; a range of values were able to get this magnetic order. [Preview Abstract] |
Wednesday, March 7, 2007 1:39PM - 1:51PM |
P11.00013: GW+exact diagonalization approach for electronic structure calculations in Mott insulators Nikolay Zein, Serguie Savrasov, Gabriel Kotliar We combine GW and exact diagonalization approaches to calculate electronic structure both in antiferromagnetic and paramagnetic states and find parameters of the corresponding Hubbard model in several transition metal oxides. We discuss extraction of double counting terms, renormalization of one-particle spectrum and interaction, mutual influence of Hubbard-like and GW contributions. Results are compared with LDA+DMFT calculations and the importance of self-consistent approach is stressed [Preview Abstract] |
Wednesday, March 7, 2007 1:51PM - 2:03PM |
P11.00014: Novel Phase Between Band and Mott Insulators in Two Dimensions Srivenkateswara Sarma Kancharla, Elbio Dagotto We investigate the ground state phase diagram of the half-filled repulsive Hubbard model in two dimensions in the presence of a staggered potential $\Delta$, the so-called ionic Hubbard model, using cluster dynamical mean field theory. We find that for large Coulomb repulsion, $U >>\Delta$, the system is a Mott insulator (MI). For weak to intermediate values of $\Delta$, on decreasing U, the Mott gap closes at a critical value $U_{c1}(\Delta)$ beyond which a correlated insulating phase suggesting bond order (BO) is found. Further, this phase undergoes a first-order transition to a band insulator (BI) at $U_{c2}(\Delta)$ with a finite charge gap at the transition. For large $\Delta$, there is a direct first-order transition from a MI to a BI with a single metallic point at the phase boundary. [Preview Abstract] |
Wednesday, March 7, 2007 2:03PM - 2:15PM |
P11.00015: Kernel sweeping method for exact diagonalization of spin models - numerical computation of a CSL Hamiltonian Darrell Schroeter, Eliot Kapit, Ronny Thomale, Martin Greiter We have recently constructed a Hamiltonian that singles out the chiral spin liquid on a square lattice with periodic boundary conditions as the exact and, apart from the two-fold topological degeneracy, unique ground state [1]. The talk will present a kernel-sweeping method that greatly reduces the numerical effort required to perform the exact diagonalization of the Hamiltonian. Results from the calculation of the model on a $4\times4$ lattice, including the spectrum of the model, will be presented. [1] D. F. Schroeter, E. Kapit, R. Thomale, and M. Greiter, \textit{Phys. Rev. Lett.} in review. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700