Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session L20: Correlated Electron Magnetism: Theory |
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Sponsoring Units: DCMP GMAG Chair: Hyowon Park, University of Illinois at Chicago Room: 280 |
Wednesday, March 15, 2017 11:15AM - 11:27AM |
L20.00001: Non-perturbative study of itinerant ferromagnetic in t$_{2g}$-orbital systems Eric Bobrow, Yi Li We study itinerant ferromagnetism in a t$_{2g}$ multi-orbital Hubbard system where electrons in each orbital band can only move parallel to the corresponding orbital orientation. Electrons in different orbital bands interact through on-site multi-orbital interactions including Hund's coupling. In this talk, we present our non-perturbative results of itinerant ferromagnetism in the strong-coupling limit, where there are no doubly occupied orbitals. By combining the multi-orbital ferromagnetism driven by Hund's coupling for quasi-one-dimensional bands together with generalized Nagaoka-type ferromagnetism, we extend these results to multi-orbital Hubbard models to show the existence of a ferromagnetic ground state in the presence of multiple holes. Possible applications to systems of transition-metal-oxide interfaces will be presented. [Preview Abstract] |
Wednesday, March 15, 2017 11:27AM - 11:39AM |
L20.00002: Orbital currents in a three-band spinless fermion lattice model Alex Liebman-Pel\'{a}ez, Darrell Schroeter We investigate the stability of orbital currents in a three-band model of the cuprates. We consider a Hubbard-type model for spinless fermions moving on an array of plaquettes that are coupled by weak hopping. The orbital current, bond density, and charge density present on an individual plaquette are associated with the components of a pseudospin located on that plaquette. An effective pseudospin Hamiltonian is derived at second order in degenerate perturbation theory that can be used to examine the stability of orbital current order in this model. This work extends the one-band model of Pujari and Henley [PRB \textbf{80}, 085116] such that it applies to orbital currents in the physically relevant three-band model. [Preview Abstract] |
Wednesday, March 15, 2017 11:39AM - 11:51AM |
L20.00003: Magnetic Field Effects on Dynamical Spectral Weight Transfer in the Hubbard Model Christian Boyd, Philip Phillips Some twenty years ago, dynamical spectral weight transfer provided the mechanism by which spectral weight in the lower Hubband band could, even at half-filling, exceed the doping level. The relative significance of dynamical spectral weight transfer depends crucially on the ground state configuration and its influence on electron hopping. Precise details about the ground state configuration may be difficult to determine; however, strong coupling transformations provide a clear picture in terms of energetically-favorable ordering within a simpler model. An external magnetic field complicates the issue by influencing magnetic order in the ground state and coupling to the hopping dynamics of the electrons. We explore the resulting changes in the dominant dynamical contributions to the spectral weight in the lower Hubbard band. [Preview Abstract] |
Wednesday, March 15, 2017 11:51AM - 12:03PM |
L20.00004: Mutual spin-charge entanglement and phase string effect: A case study by exact diagonalization of one hole doped $t$-$J$ model in one dimension Wayne Zheng, Zheng-Yu Weng A doped Mott insulator exhibits distinct properties associated with the peculiar Berry-phase structure known as the phase string. As a case study, we investigate the ground states of finite-size Heisenberg spin chains doped by one hole with numerical exact diagonalization. A series of quantum critical points with distinct crystal momenta are identified as a function of $J/t$ in each given finite-size chain, which reduces to a single phase once the phase-string Berry phase is turned off. We introduce a new kind of mutual spin-charge entanglement to characterize such different phases and phase transitions as the result of quantum interference of the phase string effect. Important physical implications inferred from the study will be discussed. [Preview Abstract] |
Wednesday, March 15, 2017 12:03PM - 12:15PM |
L20.00005: Magnetic Order-Disorder Transitions on a 1/3 -- Depleted Square Lattice Huaiming Guo, Tiago Mendes-Santos, Warren Pickett, Richard Scalettar Quantum Monte Carlo simulations are used to study the magnetic and transport properties of the Hubbard Model, and its strong coupling Heisenberg limit, on a one-third depleted square lattice. This is the geometry occupied, after charge ordering, by the spin-{\$}$\backslash $frac\textbraceleft 1\textbraceright \textbraceleft 2\textbraceright {\$} Ni{\$}\textasciicircum \textbraceleft 1$+$\textbraceright {\$} atoms in a single layer of the nickelate materials La{\$}\textunderscore 4{\$}Ni{\$}\textunderscore 3{\$}O{\$}\textunderscore 8{\$} and (predicted) La{\$}\textunderscore 3{\$}Ni{\$}\textunderscore 2{\$}O{\$}\textunderscore 6{\$}. Our model is also a description of strained graphene, where a honeycomb lattice has bond strengths which are inequivalent. For the Heisenberg case, we determine the location of the quantum critical point (QCP) where there is an onset of long range antiferromagnetic order (LRAFO), and the magnitude of the order parameter, and then compare with results of spin wave theory. An ordered phase also exists when electrons are itinerant. In this case, the growth in the antiferromagnetic structure factor coincides with the transition from band insulator to metal in the absence of interactions. [Preview Abstract] |
Wednesday, March 15, 2017 12:15PM - 12:27PM |
L20.00006: The Lieb lattice near 1/6 filling Raimundo dos Santos, Natanael Costa, Tiago Mendes-Santos, Jose Luiz Ferreira, Thereza Paiva, Richard Scalettar The interplay between van Hove singularities, nesting, and particle-hole symmetry influences the magnetic and transport properties of interacting electrons in fundamental ways. We consider a Hubbard model for interacting electrons on a Lieb lattice (or CuO$_2$ lattice) under the following simplifying assumptions: an on-site repulsion $U_d>0$ is assumed to be effective solely on Cu sites, so that $U_p=0$; vanishing site energies, $\varepsilon_d=\varepsilon_p=0$; and hopping is only allowed between Cu and O sites. For the non-interacting case at 1/6 filling (electronic density $\rho=1/3$), the density of states (DOS) displays a van Hove singularity, and the Fermi surface is nested. In order to probe the interplay between these features, we use Determinant Quantum Monte Carlo simulations and Lanczos diagonalizations (with twisted boundary conditions) to investigate the physical properties at this filling and slightly doped away from it. We identify sharp enhancement of antiferromagnetic correlations on $d$ sites exactly at this filling, due to nesting, and investigate possible Mott insulating behavior with $U_d$. Further, we examine the behavior of charge correlations, and different pairing susceptibilities in order to probe some enhancement of superconducting correlations. [Preview Abstract] |
Wednesday, March 15, 2017 12:27PM - 12:39PM |
L20.00007: On the origin of Mott transition and fractionalized spin liquids Ziqiang Wang, Long Liang, Sen Zhou An analytical solution of the Mott transition is obtained for the Hubbard model on the Bethe lattice in the large coordination number ($z$) limit. The excitonic binding of the doublons and holons is shown to be the origin of a continuous Mott transition between a metal and an emergent quantum spin liquid insulator where the opening of the Mott gap and the vanishing of the quasiparticle coherence coincide at the same critical $U_c$. The doublon-holon binding theory enables a different large-$z$ limit and a different phase structure than the dynamical meanfield theory (DMFT) by allowing intersite spinon correlations to lift the $2^N$-fold degeneracy of the local moments. We show that the spinons are coupled to doublons/holons by a dissipative compact U(1) gauge field that is in the deconfined phase, stabilizing the spin-charge separated gapless spin liquid Mott insulator. [Preview Abstract] |
Wednesday, March 15, 2017 12:39PM - 12:51PM |
L20.00008: Commensurate and incommensurate SDW and the superconducting dome in heavy electron systems Pedro Schlottmann A nested Fermi surface together with interactions between the carriers may give rise to itinerant AF. We consider an electron and a hole pocket, separated by a wave vector ${\bf Q}$, and Fermi momenta $k_{F1}$ and $k_{F2}$, respectively. The order is gradually suppressed by increasing the mismatch of the Fermi momenta and a QCP is obtained as $T_N \to 0$. If ${\bf Q} = {\bf G}/2$ (Umklapp), pairs of electrons can be transferred between the pockets. This process may lead to superconductivity and we investigate the conditions for a superconducting dome above the QCP [1]. If ${\bf Q} \neq {\bf G}/2$ eight phases need to be considered: commensurate and incommensurate SDW and CDW and four superconductivity phases, two of them with space modulated order parameter of the FFLO type with wave number $|{\bf Q} - {\bf G}/2|$. The RG equations are studied and a phase diagram with re-entrant SDW is obtained [2]. \vskip 0.05in \par\noindent [1] P. Schlottmann, Phys. Rev. B {\bf 89}, 014511 (2014). \par\noindent [2] P. Schlottmann, Phys. Rev. B {\bf 92}, 045115 (2015). [Preview Abstract] |
Wednesday, March 15, 2017 12:51PM - 1:03PM |
L20.00009: Giant Spin Gap and Magnon Localization in the Disordered Heisenberg Antiferromagnet Sr2Ir1-xRuxO4 Yue Cao, Xuerong Liu, Wenhu Xu, Weiguo Yin, Derek Meyers, Jungho Kim, Diego Casa, Mary Upton, Thomas Gog, Tom Berlijn, Gonzalo Alvarez, Shujuan Yuan, Jasminka Terzic, J. M. Tranquada, John Hill, Gang Cao, Robert Konik, M. P. M. Dean We study the evolution of magnetic excitations in the disordered two-dimensional antiferromagnet Sr\textunderscore 2Ir\textunderscore 1-xRu\textunderscore xO\textunderscore 4. A gigantic magnetic gap greater than 40 meV opens at x $=$ 0.27 and increases with Ru concentration, from 40 meV to \textgreater 150 meV, rendering the dispersive magnetic excitations in Sr2IrO4 almost momentum independent. Up to a Ru concentration of x $=$ 0.77, both experiments and first-principles calculations show the Ir J\textunderscore eff $=$ 1/2 state remains intact. The magnetic gap arises from the local interaction anisotropy in the proximity of the Ru disorder. Under the coherent potential approximation, we reproduce the experimental magnetic excitations using the disordered Heisenberg antiferromagnetic model with suppressed next-nearest neighbor ferromagnetic coupling. Ref: Y. Cao et al., arXiv:1608.04640 (2016). [Preview Abstract] |
Wednesday, March 15, 2017 1:03PM - 1:15PM |
L20.00010: A correlated Anderson insulator on the honeycomb lattice Lufeng Zhang, Chia-Chen Chang, Hsiang-Hsuan Hung, Tianxing Ma, Richard T. Scalettar We study the effect of disorder on the semimetal -- Mott insulator transition in the half-filled repulsive Hubbard model on a honeycomb lattice, a system that features vanishing density of states at the Fermi level. Using the determinant quantum Monte Carlo method, we characterize various phases in terms of the bulk-limit antiferromagnetic (AF) order parameter, compressibility, and temperature-dependent DC conductivity. In the clean limit, our data are consistent with previous results showing a single quantum critical point separating the semi-metallic and AF Mott insulating phases. With the presence of randomness, a non-magnetic disordered insulating phase emerges. Inside this disordered insulator phase, there is a crossover from a gapless Anderson-like insulator to a gapped Mott-like insulator. [Preview Abstract] |
Wednesday, March 15, 2017 1:15PM - 1:27PM |
L20.00011: DMRG simulations of SU(N) Heisenberg models using a million of states Andreas Weichselbaum, Sylvain Capponi, Andreas L{\"a}uchli, Alexei Tsvelik, Philippe Lecheminant The density matrix renormalization group (DMRG) is applied to SU($N$) symmetric Heisenberg chains and ladders while fully exploiting the underlying SU($N$) symmetry. Since these models can be motivated from symmetric $N$-band fermionic models, it is immediately clear that the numerical complexity of simulating SU($N$) symmetric models grows exponentially in $N$. Nevertheless in the presence of symmetry this exponential growth is largely transferred to the symmetry multiplets in that the largest multiplets that appear in the simulation typically grow in size like $10^{N-1}$. Therefore while keeping a moderate number of multiplets, the full state space dimension required for converged results can quickly reach a million of states. Recent results on Heisenberg ladders with $N\leq 4$ and varying rung coupling are discussed and contrasted to existing literature. [Preview Abstract] |
Wednesday, March 15, 2017 1:27PM - 1:39PM |
L20.00012: Topological Mott insulator on the checkerboard lattice with a quadratic band crossing Shoushu Gong, Kun Yang, Oskar Vafek We study quantum anomalous Hall (QAH) phase of spinless fermions on a checkerboard lattice at half filling using density matrix renormalization group. This system has a quadratic band crossing point in the absence of interaction. With growing nearest-neighbor ($V_1$) and second-neighbor ($V_2$) repulsive interactions, we identify a nematic Mott insulator phase in the $V_1$ dominant regime and a stripe charge density wave phase in the $V_2$ dominant regime. In the intermediate regime, we identify a QAH phase induced by interactions, which spontaneously breaks time reversal symmetry. By threading a U(1) charge flux $\theta$ in the cylinder, we find charge pumping from one edge to the other with increasing flux, which gives a quantized topological Chern number $C = 1$ at $\theta = 2\pi$ that characterizes gapless edge states. In the weak interaction regime, we do not find any symmetry breaking on our studied system size. Interestingly, with increasing cylinder width, nonzero chiral order emerges at the smaller interaction, which suggests that the weak interaction regime is likely to be also a QAH phase, which however is too weak to be detected by our finite-size calculations. [Preview Abstract] |
Wednesday, March 15, 2017 1:39PM - 1:51PM |
L20.00013: Diagrammatic Monte Carlo Dual Fermions study of the 2D Hubbard model Sergei Iskakov, Emanuel Gull The dual fermion series is a diagrammatic approach for correlated lattice models that includes non-perturbative local and perturbative non-local dynamic correlations. In this talk we show results from a simulation of the 2D Hubbard model solved with dual fermions, where we stochastically sample the dual fermion perturbation series using a diagrammatic Monte Carlo method. We present a description of the method, compare to other methods, and show several applications to correlated systems. [Preview Abstract] |
Wednesday, March 15, 2017 1:51PM - 2:03PM |
L20.00014: Doped quasi-two-dimensional Hubbard model--stripes and superconductivity Chia-Min Chung, Steven White We study the ground state of hole-doped Hubbard model on cylinders in the parameter region relevant to cuprate superconductors using Density Matrix Renormalization Group method. The ground states we find are striped states with coexisting charge density wave and antiferromagnetic order. We discuss the competing energies between striped states of different wave lengths. The d-wave pairing in the striped states is also discussed. [Preview Abstract] |
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