Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session U44: Models of Strongly Correlated Electrons |
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Sponsoring Units: DCMP Chair: S.-W. Tsai, University of California, Riverside Room: Baltimore Convention Center 347 |
Thursday, March 16, 2006 8:00AM - 8:12AM |
U44.00001: First-principles calculations of magnetic transition temperatures Xiangang Wan, Sergey Savrasov We introduce a method to evaluate magnetic transition temperatures of strongly correlated systems. It is based on a combination of dynamical mean field theory, the local density functional theory, and employs ``magnetic force theorem'' for evaluating exchange constants. The method automatically predicts at a given temperature whether the system is ordered or disordered magnetically. We illustrate the approach on several systems, and discuss its accuracy in comparison with the experiment. The effect of electron-electron correlations on these predictions will be discussed. [Preview Abstract] |
Thursday, March 16, 2006 8:12AM - 8:24AM |
U44.00002: Electron-phonon-coupling-driven pairing symmetry transition in a ladder Ka-Ming Tam, Antonio H. Castro Neto, Shan-Wen Tsai, David K. Campbell We address the effects of electron-phonon coupling in the electron-electron interacting ladder using the recently developed functional renormalization group method, in which the full retardation effects can be taken into account impartially\footnote{S.-W. Tsai, A.H. Castro Neto, R. Shankar, D.K. Campbell, Phys. Rev. B 72, 054531 (2005)}. We study the doped Holstein-Hubbard ladder as a typical example and show that there is a transition between s-wave and d-wave pairing as a function of electron-phonon coupling and doping level. This contrasts with recent results from a two-step renormalization group, which suggest that the electron-phonon coupling only contributes in a subdominant fashion and that the spin-gapped pairing phase always has d-wave symmetry, unchanged from the doped Hubbard ladder without electron-phonon interaction\footnote{Alexander Seidel, Hsiu-Hau Lin, Dung-Hai Lee, Phys. Rev. B 71, 220501 (2005)}. [Preview Abstract] |
Thursday, March 16, 2006 8:24AM - 8:36AM |
U44.00003: Dynamical Mean Field Study of the Extended Hubbard Model Andrew Baldwin, Alexandru Macridin, Mark Jarrell, Richard Scalettar The competition between on-site $U$ and intersite $V$ repulsion in the extended Hubbard model drives ground state phase transitions between spin density wave (sdw) and charge density wave (cdw) phases. While it was originally thought that in one dimension the sdw-cdw transition was first order at strong coupling and second order at weak coupling, it is now known that for small $U$ and $V$ a bond ordered wave phase intervenes. Here we present studies of the extended Hubbard model using the dynamical cluster approximation. We study the influence of $V$ on the CDW and SDW transition temperatures, $T_c$ and $T_N$. We find $T_N$ is almost unmodified in the sdw region, even if $J=4t^2/(U-V)$ is strongly modified. We also study the effect of V on the pairing interaction and the pseudogap. [Preview Abstract] |
Thursday, March 16, 2006 8:36AM - 8:48AM |
U44.00004: Exact transformation for spin-charge separation of spin half fermions Stellan \"{O}stlund, Mats Granath We demonstrate an exact local transformation which maps a purely Fermionic manybody system to a system of spinfull Bosons and spinless Fermions, demonstrating a possible path to a non-Fermi liquid state. We apply this to the half-filled Hubbard model and show how the transformation maps the ordinary spin half Fermionic degrees of freedom exactly and without introducing Hilbert space constraints to a charge-like ``quasicharge'' fermion and a spin-like ``quasispin'' Boson while preserving all the symmetries of the model. We present approximate solutions with localized charge which emerge naturally from the Hubbard model in this form. Our results strongly suggest that charge tends to remain localized for large values of the Hubbard U. The results suggest that checkerboard patterns are natural patterns that result for the strongly interacting Hubbard model away from half filling. [Preview Abstract] |
Thursday, March 16, 2006 8:48AM - 9:00AM |
U44.00005: Dynamical Cluster Approximation Study of Ferromagnetism in the Periodic Anderson Model Muhammad Aziz Majidi, Mark Jarrell, Juana Moreno, Sumith Doluweera The ferromagnetic phase in the strong coupling limit of the Periodic Anderson Model (PAM) is not fully understood. Previous studies using the Dynamical Mean Field Approximation (DMFA) (Tahvildar-Zadeh {\it et al.} (PRB {\bf 55}, R3332 (1997)) pointed to the importance of a ferromagnetic mechanism other than RKKY at conduction-band fillings near a quarter. This mechanism is related to the formation of a charge-density wave of the conduction electrons. However, it is questionable whether or not this effect persists when non-local correlations are incorporated into the theory. We try to answer this question by performing parametric studies on the phase diagram, the RKKY coupling, and the charge and spin susceptibilities for a three-dimensional system using the Dynamical Cluster Approximation (DCA). [Preview Abstract] |
Thursday, March 16, 2006 9:00AM - 9:12AM |
U44.00006: Phase Diagrams of Hubbard Models with Small Unit Cells Wei-Feng Tsai, Steven A. Kivelson We present a controlled approach to the low temperature phase diagram of highly inhomogeneous Hubbard models in the limit of small coupling, $t'$, between clusters. We apply this to the dimerized and checkerboard models with any strength of $U$. The dimerized model is found to behave like a doped semiconductor, with a Fermi-liquid groundstate with parameters ({\it e.g.} the effective mass) which are smooth, and unspectacular functions of $U$. By contrast, the checkerboard model has a Fermi liquid phase at large $U > U_c = 4.67$, a d-wave superconducting state with a full gap for $U_c > U > 0$, and a narrow strip of an intermediate d-wave superconducting phase with gapless ``nodal'' quasiparticles for $|U - U_c| < {\cal O}(t^\prime)$. [Preview Abstract] |
Thursday, March 16, 2006 9:12AM - 9:24AM |
U44.00007: Effects of interplay between electron-electron and electron-phonon interactions in two-dimensional systems Filippos Klironomos, Shan-Wen Tsai We study the two-dimensional Hubbard model in the presence of electron-phonon interaction which is integrated into an effective electron-electron coupling producing a retardation effect [S.-W. Tsai {\it et al} Phys. Rev. B {\bf 72}, 054531 (2005)]. We work in the context of the functional renormalization group method [R. Shankar, Rev. Mod. Phys. {\bf 66}, 129 (1994)] to one loop accuracy, where self-energy corrections are included, and investigate the effect that isotropic and anisotropic phonons have near van Hove band fillings. This approach conveniently takes into consideration the effect of phonons at every step of the renormalization group method. We focus on the two-patch and many-patch schemes, where the Fermi surface is subdivided into two or multiple patches that label the electrons involved in each interaction process and produce a phase diagram for the different instabilities associated with the Hubbard model. We also depart from half-filling and investigate various specific cases of momentum transfer as well. [Preview Abstract] |
Thursday, March 16, 2006 9:24AM - 9:36AM |
U44.00008: Nearest-Neighbor Repulsion and Competing Charge and Spin Order in the Extended Hubbard Model. Davoudi Bahman, A.-M.S. Tremblay We generalize the Two-Particle Self-Consistent (TPSC) approach to study the extended Hubbard model where the nearest-neighbor interaction $V$ is present in addition to the local interaction $U$. Our results are in good agreement with available Quantum Monte-Carlo results over the whole range of density $n$ up to intermediate coupling. As a function of $U, V$ and $n$ we observe different kinds of charge and spin orders, like commensurate/incommensurate charge and spin density wave, phase separation, and ferromagnetic order. For attractive $V$ superconductivity could exist in the regions where the other types of charge and spin orders do not dominate. Ref.: B. Davoudi and A.-M.S. Tremblay, cond-mat/0509707 [Preview Abstract] |
Thursday, March 16, 2006 9:36AM - 9:48AM |
U44.00009: Quantum Monte Carlo Study of the Triangular Hubbard Model Christopher Varney, Richard Scalettar, Mark Jarrell, Alexandru Macridin We study the Hubbard model on a triangular lattice using Determinant Quantum Monte Carlo and the Dynamic Cluster Approximation. We compare the spin, charge and pairing response functions obtained with the two methods as a function of spatial lattice and cluster size, and also compute the one particle spectrum. We examine the possibility of charge ordering at one third filling driven by the avoidance of magnetic frustration. [Preview Abstract] |
Thursday, March 16, 2006 9:48AM - 10:00AM |
U44.00010: Theory of Cu K-edge Resonant Inelastic X-ray Scattering in Cuprates. Kenji Tsutsui, Takami Tohyama, Sadamichi Maekawa Resonant inelastic x-ray scattering (RIXS) has received much attention as a powerful technique to investigate elementary excitations in strongly correlated electron systems. In particular, the momentum-dependent spectra of Cu K-edge RIXS in high-Tc cuprates have been obtained by several experimental groups. The knowledge of these excitations across the gap as well as single-particle excitations is of importance for understanding the electronic properties in cuprates. We demonstrate theoretically momentum dependences of the RIXS in insulating and doped cuprates. The RIXS spectra are calculated by using the exact diagonalization techniques on small clusters in two-dimensional Hubbard models with 1s-core bands. In the insulating case, we find the anisotropic momentum dependence in the RIXS spectrum. The dependence is explained by the particle-hole excitations in which the antiferromagnetic correlation of the ground state plays a crucial role. Upon hole-doping, the spectrum from the lower Hubbard band to the upper Hubbard band becomes broad and less momentum dependent. This is in contrast to the case of electron-doping, where the momentum dependence of the spectrum in the undoped system remains, except that along the $<$1,0$>$ direction. The difference in the spectra between hole- and electron-doped systems follows the carrier-dependence of short-range AF spin correlations. [Preview Abstract] |
Thursday, March 16, 2006 10:00AM - 10:12AM |
U44.00011: Fermi Surface of the Half Heusler Compounds Ce$_{1-x}$La$_{x}$BiPt A. D. Bianchi, J. Wosnitza, N. Kozlova, D. Eckert, L. Schultz, I. Ophale, S. Elgazzar, M. Richter, J. Hagel, M. Doerr, G. Goll, H. v. L\"ohneysen, G. Zwicknagl, T. Yoshino, T. Takabatake We report on the Fermi surface in the correlated half-Heusler compound Ce$_{1-x}$La$_{x}$BiPt. In CeBiPt we find a field-induced change of the electronic band structure as discovered by electrical-transport measurements in pulsed magnetic fields. For magnetic fields above $\sim$25~T, the charge-carrier concentration determined from Hall-effect measurements increases nearly 30\%, whereas the Shubnikov--de Haas (SdH) signal disappears at the same field. In the non-$4f$ compound LaBiPt the Fermi surface remains unaffected, suggesting that these features are intimately related to the Ce 4$f$ electrons. Electronic band-structure calculations point to a $4f$-polarization-induced change of the Fermi-surface topology. In order to test this hypothesis, we have measured the (SdH) signal in a Ce$_{0.95}$La$_{0.05}$BiPt sample with a low La concentration. [Preview Abstract] |
Thursday, March 16, 2006 10:12AM - 10:24AM |
U44.00012: Charge Physics of the Falicov-Kimball Model Philip Brydon, Miklos Gulacsi The charge-ordered phases of the one-dimensional Falicov-Kimball model are examined using a non-perturbative representation of the itinerant electrons. An effective model allows us to understand the competition between phase separation and long-range order. We construct a ground-state phase diagram for partial band-filling. The addition of an on-site hybridization potential is found to significantly alter the form of the phase diagram, with the appearance of mixed-valence phenomena. [Preview Abstract] |
Thursday, March 16, 2006 10:24AM - 10:36AM |
U44.00013: Application of LDA+DMFT to systems near volume collapse transition Kristjan Haule The physical origin of the volume collapse transition in Cerium and related materials will be addressed. Using recently developed self-consistent LDA+DMFT method, we will show that the Kondo Volume collapse model, involving both the f and spd electrons, describes the optical data better than a Mott transition picture. We predict the full temperature dependence of the optical spectra and find the development of a hybridization pseudogap in the vicinity of the collapse transition. [Preview Abstract] |
Thursday, March 16, 2006 10:36AM - 10:48AM |
U44.00014: Functional renormalization group analysis of the one-dimensional half-filled Holstein-Hubbard model Shan-Wen Tsai, Ka-Ming Tam, David K. Campbell, Antonio H. Castro Neto The one-dimensional half-filled Holstein-Hubbard model (HHM) is studied by the newly developed electron-phonon coupled functional renormalization group (ep-FRG) [1]. The ep-FRG enables us to study the electron-phonon coupled system in an unbiased manner by taking account of the scatterings at different energy scales and momenta systematically. Previous studies of the half-filled HHM showed that there is a direct transition between the charge-gapped spin-density wave (SDW) phase and the spin-charge-gapped charge-density wave (CDW) phase. Recently, it has been proposed that there is an intermediate spin-gapped metallic phase with dominant superconducting (SC) pairing correlation between SDW phase and CDW phase [2]. Our ep-FRG results show that the dominant correlation in this intermediate phase is not SC pairing. \vskip 0.3cm \noindent [1] S.-W. Tsai, A. H. Castro Neto, R. Shankar, and D. K. Campbell, Phys. Rev. B 72, 054531 (2005). \vskip 0.1cm \noindent [2] R. T. Clay and R. P. Hardikar, Phys. Rev. Lett. 95, 096401 (2005). [Preview Abstract] |
Thursday, March 16, 2006 10:48AM - 11:00AM |
U44.00015: Antiferromagnetism and hot spots in CeIn3 Pavel Grigoriev, Lev Gor'kov Enormous mass enhancement at ``hot spots'' on the Fermi surface (FS) of the antiferromagnetic CeIn$_3$ has been reported at strong magnetic field near its antiferromagnetic quantum critical point [T. Ebihara et al., Phys. Rev. Lett. 93, 246401 (2004)]. The effect was ascribed to anomalous spin fluctuations at these spots owing to peculiar strong many-body interactions. The ``hot spots'' lie at the positions on FS same as in non-magnetic LaIn$_3$ where the narrow necks are protruded, thus, hinting on their possible relation. Assuming that in paramagnetic phase CeIn$_3$ has similar spectrum, we study the influence of the antiferromagnetic ordering (AFM) on the energy spectrum of CeIn$_3$ and show that its FS undergoes a topological change at the onset of AFM. The necks at the ``hot spots'' are truncated by the AFM, thus restoring the almost spherical d-part of the FS of CeIn$_3$. Applied field suppresses the AFM and restores the necks on the FS (so-called 2.5-order phase transition) leading to logarithmic divergence of the dHvA effective mass when the electron trajectory passes near or through the restored necks. This effect fully explains the observed dHvA mass enhancement in the ``hot spots'' in the frameworks of one-particle approximation and leads to the predictions concerning the spin-dependence of the effective electron mass. [Preview Abstract] |
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