Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session J40: Strongly Correlated Models for Cuprate Systems |
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Sponsoring Units: DCMP Chair: Philip Phillips, University of Illinois at Urbana-Champaign Room: F151 |
Tuesday, March 16, 2010 11:15AM - 11:27AM |
J40.00001: Enhancement of superconductivity in a striped 2D Hubbard model Thomas Maier, Gonzalo Alvarez, Michael Summers, Thomas Schulthess Recent photoemission and transport measurements have shown that superconductivity in some respects is optimized in the striped state at 1/8 doping in LaBaCuO. To understand this phenomenon, we use dynamic cluster quantum Monte Carlo simulations to study the superconducting behavior of a 1/8 doped two-dimensional Hubbard with imposed uni-directional stripe-like charge modulation. Consistent with experiments, we find a significant increase of the pairing correlations and critical temperature relative to the homogeneous system when the modulation length-scale is sufficiently large. Using a separable form of the irreducible particle-particle vertex, we find that a delicate balance between the modulation enhanced pairing interaction, and modulation reduced hole-mobility is found to result in optimized superconductivity for moderate modulation strength. [Preview Abstract] |
Tuesday, March 16, 2010 11:27AM - 11:39AM |
J40.00002: Exact Diagonalization Study of Superconductivity in the 2D Hubbard Model Chunjing Jia, Cheng-Chien Chen, Brian Moritz, Thomas Devereaux, Sriram Shastry The two dimensional (2D) Hubbard model in the intermediate coupling limit is believed to capture the essential physics of high-Tc cuprates in the low energy sector. Extensive numerical studies, using small clusters, have demonstrated that the 2D Hubbard model contains much of the key physics in these materials including a Mott insulating, antiferromagnetic ground state at half-filling and d-wave superconductivity with subsequent hole-doping. To investigate the conjecture that the Hubbard Model has a superconducting groundstate, we study an extension of the Hubbard Model including an infinite-range pair-field term which precipitates superconducitivity in the d-wave channel. We study the states of the model as a function of the strength of this pairing term. We calculate observables such as the d-wave condensate occupation, fidelity and the ratio between the two lowest natural orbitals of the pair-field density matrix. We also consider the effect longer range hopping on the model. Calculations show that the Hubbard model favors a superconducting groundstate for some parameters, longer range hopping plays an important role. The numerical results have been obtained using a combination of LAPACK, (P)ARPACK, and Lanczos exact diagonalization techniques. [Preview Abstract] |
Tuesday, March 16, 2010 11:39AM - 11:51AM |
J40.00003: Attractive Hubbard model with inhomogeneous interactions Vijay B. Shenoy I shall discuss the phase diagram of the attractive Hubbard model with spatially inhomogeneous interactions obtained using a single site dynamical mean field theory like approach. The model is characterized by three parameters: the interaction strength, the active fraction (fraction of sites with the attractive interaction), and electron filling. I show that in a parameter regime with intermediate values of interaction strength (compared to the bare bandwidth of the electrons), and intermediate values of the active fraction, ``non-BCS'' superconductivity is obtained. The results of this work are likely to be relevant to many systems with spatially inhomogeneous superconductivity such as strongly correlated oxides, systems with negative $U$ centers etc. [Preview Abstract] |
Tuesday, March 16, 2010 11:51AM - 12:03PM |
J40.00004: Numerical study of the bond order in 2D Hubbard model Shuxiang Yang, Zhaoxin Xu, Subir Sachdev, Mark Jarrell We study the bond order for 2D repulsive Hubbard model using the dynamical cluster approximation. The z-component of the spin operator product and the so-called bond-order-wave operator are used to detect the divergence of the bond susceptibility. Different bond ordering patterns, such as the column state and staggered state, are analyzed and compared in the pseudo-gap region and their relations to the quantum criticality are explored. [Preview Abstract] |
Tuesday, March 16, 2010 12:03PM - 12:15PM |
J40.00005: Superconductivity in the repulsive Hubbard model: an asymptotically exact weak-coupling solution Steven Kivelson, Srinivas Raghu, Douglas Scalapino We study the superconducting instability of the Hubbard model in the limit where U, the onsite repulsive interaction, is much smaller than the electron hopping. We present an asymptotically exact expression for Tc, the superconducting transition temperature, in terms of the correlation functions of the non-interacting system which remains valid for arbitrary densities so long as the interactions are sufficiently small. Our strategy for computing Tc involves first integrating out all degrees of freedom having energy higher than an arbitrarily chosen initial cutoff. The renormalization group (RG) flows of the resulting effective action are computed and Tc is obtained by determining the scale below which the RG flows in the Cooper channel break down. Using this method, we present results of Tc and pairing symmetries as a function of electron concentrations for a wide variety of lattice systems in two and three dimensions. [Preview Abstract] |
Tuesday, March 16, 2010 12:15PM - 12:27PM |
J40.00006: Determinant Quantum Monte Carlo Studies of the Single-band Hubbard-Holstein Model Steven Johnston, B. Moritz, R.T. Scalettar, T.P. Devereaux The role of the electron-phonon (el-p) interaction in strongly correlated systems, such as the transition metal oxides, has attracted considerable interest. In this talk we will present Determinant Quantum Monte Carlo results on the single-band Hubbard-Holstein model at half-filling. The competition between charge-density wave, antiferromagnetic and superconducting order will be examined as a function of temperature, el-ph coupling strength and Hubbard U. Here, we report a suppression of antiferromagnetic order with increasing el-ph coupling with a marked increase in this effect as the polaronic limit is reached. In addition, the impact of the el-ph interaction on the single-particle spectral function will be presented for both the weak and strong el-ph coupling limits. [Preview Abstract] |
Tuesday, March 16, 2010 12:27PM - 12:39PM |
J40.00007: Identifying the origin of Superconducting pairing in the QCP vicinity by scaling analysis of dynamical cluster quantum Monte Carlo simulation data Shi-Quan Su, Peter Reis, Herbert Fotso, Zhaoxin Xu, Khatami Ehsan, Karlis Mikelsons, Shuxiang Yang, Dimitris Galanakis, Juana Moreno, Mark Jarrell In the phase diagram of 2D Hubbard model describing the physics of high temperature superconductor, the superconducting dome at the vicinity of the quantum critical point (QCP) persist the scaling properties similar with the case exactly on the QCP A simple phenomenological scaling theory proposed by Jan Zaanen et al. (arXiv:0905.1225v2) suggests that in the proximity of the superconducting dome the QCP generates a condition whereby in its vicinity, any weak retarded interaction will generate pairing i.e., the pairing fluctuations near the QCP are relevant. To test this hypothesis in the strong correlated many-body system, 2D Hubbard model, which beyonds the capability of perturbation type theoretical study, we will calculate the dressed single-particle Green's function bubble d-wave projected dynamic pair susceptibility within the framework of Dynamical Cluster Quantum Monte Carlo (DCA) simulation and Maximum Entropy Method (MEM), and inspect its frequency and temperature dependence to identify different susceptibility channels in the system are relevant or not. [Preview Abstract] |
Tuesday, March 16, 2010 12:39PM - 12:51PM |
J40.00008: Enhanced pairing in the checkerboard Hubbard ladder George Karakonstantakis, Erez Berg, Steven Kivelson, Steven White We study the repulsive Hubbard two-leg ladder model with various forms of inhomogeneity using the density matrix renormalization group method. For instance, we consider the case in which the hopping matrix elements $t_{ij}$ are periodically modulated so that the ladder consists of an array of $2\times 2$ plaquettes with couplings $t_{ij}=t$ within a plaquette and $t_{ij}=t' \leq t$ between plaquettes. In this ``checkerboard'' case, both the spin gap and the pair binding energy are maximized for an intermediate value of the inter-plaquette coupling, $t'\sim t/2$. This enhancement of the pairing signatures seems to be special to breaking the ladder into plaquettes, and does not occur for other forms of inhomogeneity which were explored, e.g. a site-centered charge density wave. The Luttinger exponent $K_c$ is found to be nearly independent of the inter-plaquette coupling. For an array of weakly coupled Hubbard ladders, this implies that the superconducting critical temperature T$_c$ can be increased by breaking each ladder into plaquettes. [Preview Abstract] |
Tuesday, March 16, 2010 12:51PM - 1:03PM |
J40.00009: Fermi surface topology in the proximity to the Mott insulator Youhei Yamaji, Masatoshi Imada Since the discovery of cuprate superconductors, how its low energy electronic excitations evolve with doping has attracted much attention. The normal metallic state offers a typical example of strongly correlated metallic state. Recent experiments suggest the existence of the k-dependent renormalized quasiparticle [1], or more drastic reconstruction of the Fermi surface [2]. Numerical theories on the two-dimensional Hubbard model also predict the reconstruction of the Fermi surface [3]. We propose a scenario for the Fermi surface reconstruction in the proximity to the Mott insulator based on the simple slave-boson mean-field theory [4] including charge fluctuations [5]. The key idea is the emergence of new fermionic excitations consisting of charge bosons and low energy coherent electrons, and occurrence of topological changes in the Fermi surface. We also discuss relation between the topological changes and superconductivities. [1] As a review, A. Damascelli, Z. Hussain, and Z.-X. Shen, Rev. Mod. Phys. 75, 473 (2003). [2] J. Meng, et al., arXiv: 0906.2682v1. [3] For example, T. D. Stanescu and G. Kotliar, Phys. Rev. B 74, 125110 (2006). [4] G. Kotliar, and A. E. Ruckenstein: Phys. Rev. Lett. 57, 1362 (1987). [5] R. Raimondi, and C. Castellani; Phys. Rev. B 48, 11453 (1993). [Preview Abstract] |
Tuesday, March 16, 2010 1:03PM - 1:15PM |
J40.00010: Dynamic Hubbard model: Results from dynamical mean field theory Giang Bach, Jorge Hirsch, Frank Marsiglio The dynamic Hubbard model, in which a pseudo-spin field is used to model orbital relaxation effects due to double occupancy, is investigated using the two-site dynamical mean field approximation at zero temperature. Near half-filling the Mott physics associated with the static Hubbard model is enhanced by the coupling to this auxiliary field. More importantly, the dynamic Hubbard model is strongly electron-hole asymmetric, as can be readily seen for a number of properties. We compute the quasiparticle spectral weight and the frequency dependent spectral function to illustrate some generic features of this model. In particular, holes tend to be heavier than electrons. In the anti-adiabatic limit $\omega_0 \rightarrow \infty$, where $\omega_0$ is the pseudo-spin characteristic energy, the linear dependence of the quasiparticle weight on filling shows good agreement with a previously known analytical result in the correlated hopping model. [Preview Abstract] |
Tuesday, March 16, 2010 1:15PM - 1:27PM |
J40.00011: Diagrammatic Monte Carlo for Correlated Fermions Evgeny Kozik, Kris Van Houcke, Emanuel Gull, Lode Pollet, Nikolay Prokof'ev, Boris Svistunov, Matthias Troyer We show that Monte Carlo sampling of the Feynman diagrammatic series (DiagMC) can be used for tackling hard fermionic quantum many-body problems in the thermodynamic limit by presenting accurate results for the repulsive Hubbard model in the correlated Fermi liquid regime. Sampling Feynman's diagrammatic series for the single-particle self-energy we can study moderate values of the on-site repulsion ($U/t \sim 4$) and temperatures down to $T/t=1/40$. We compare our results with high temperature series expansion and with single-site and cluster dynamical mean-field theory. [Preview Abstract] |
Tuesday, March 16, 2010 1:27PM - 1:39PM |
J40.00012: The $t$--$J$ model for Cu$_2$O$_5$ coupled ladders in Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$ Krzysztof Wohlfeld, Andrzej M. Oles, George A. Sawatzky Starting from the proper charge transfer model for Cu$_2$O$_5$ coupled ladders in Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$ in the strongly correlated regime, we derive the low energy Hamiltonian for this system with superexchange $J$ and the effective $d-d$ hopping $t$. It occurs that the widely used ladder $t$--$J$ model is not sufficient and has to be supplemented by the Coulomb repulsion between doped holes in the neighboring ladders. Next, we show how a simple mean-field solution of this extended $t$--$J$ model may explain the onset of the experimentally observed charge density wave with the odd (three or five) period in Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$. This suggests that it is not the bare ladder $t$--$J$ model but the extended $t$--$J$ model which should be used as the starting point for the explanation of the superconductivity observed under pressure in the Cu$_2$O$_5$ coupled ladders in Sr$_{0.4}$Ca$_{13.6}$Cu$_{24}$O$_{41}$. [Preview Abstract] |
Tuesday, March 16, 2010 1:39PM - 1:51PM |
J40.00013: Emergent non-Fermi liquid in the pseudogap phase of the underdoped cuprates Tanmoy Das, R. S. Markiewicz, A. Bansil As the cuprates approach the Mott insulator limit, they display a remarkable gossamer-like structure: the near-Fermi level dispersion remains nearly unrenormalized while the corresponding spectral weight tends to vanish at half filling[1]. This unusual behavior cannot be understood by conventional Fermi liquid theory where both features are controlled by a single renormalization factor. We find that while the fluctuation spectrum remains nearly isotropic in cuprates, the competing order pseudogap (here modelled as antiferromagnetism) breaks the crystal symmetry and thus promotes a strong momentum dependence in the self-energy term[2]. At half-filling, this yields an essentially unrenormalized quasiparticle dispersion which approaches the uncorrelated limit, while in sharp contrast the quasiparticle spectral weight renormalizes to zero. These opposing tendencies of dispersion and spectral weight renormalization conspire in such a way that the specific heat remains Fermi liquid like in character at all dopings in accord with experiments. Work supported in part by the USDOE. [1] S. Sahrakorpi, {\it et al.}, Phys. Rev. B {\bf 78}, 104513 (2008). [2] T. Das, {\it et al.}, arXiv:0807.4257. [Preview Abstract] |
Tuesday, March 16, 2010 1:51PM - 2:03PM |
J40.00014: Intermediate coupling phase diagrams of the cuprates Robert Markiewicz, Jose Lorenzana, Goetz Seibold, Arun Bansil We analyze the competing (non-superconducting) phases in the cuprates in the intermediate coupling regime via Gutzwiller approximation (GA) + RPA. The magnetic GA+RPA phase diagram was benchmarked for the $t-t'-U$ model[1]. The leading instabilities are associated with Fermi surface nesting, generally corresponding to a double nesting criterion, and are different for different cuprates. While electron-doped cuprates are generally associated with commensurate $(\pi ,\pi )$ nesting [2], there are competing incommensurate phases in the hole doped cuprates. Magnetic and charge-order phase diagrams will be compared. [1] L.F. Tocchio, {\it et al.}, Phys. Rev. B{\bf 78}, 041101(R) (2008). [2] C. Kusko, {\it et al.}, Phys. Rev. B. {\bf{66}}, 140513(R) (2002); T. Das, {\it et al.}, Phys. Rev. Lett. {\bf{98}}, 197004 (2007). [Preview Abstract] |
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