Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session B37b: Competing Order in Correlated Electrons |
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Sponsoring Units: DCMP Chair: Hermann Suderow, Univ Autonoma de Madrid Room: 384 |
Monday, March 13, 2017 11:15AM - 11:27AM |
B37b.00001: A parity-breaking electronic nematic phase transition in the spin-orbit coupled correlated metal Cd$_2$Re$_2$O$_7$ J. W. Harter, Z. Y. Zhao, J.-Q. Yan, D. G. Mandrus, D. Hsieh Strong interactions between electrons are known to drive metallic systems toward a variety of well-known symmetry-broken phases, including superconducting, electronic liquid crystalline, and charge- and spin-density wave ordered states. In contrast, the electronic instabilities of correlated metals with strong spin-orbit coupling have only recently begun to be explored. We uncover a novel multipolar nematic phase of matter in the metallic pyrochlore Cd$_2$Re$_2$O$_7$ using spatially-resolved second-harmonic optical anisotropy measurements. Like previously discovered electronic liquid crystalline phases, this multipolar nematic phase spontaneously breaks rotational symmetry while preserving translational invariance. However, it has the distinguishing property of being odd under spatial inversion, which is allowed only in the presence of spin-orbit coupling. By examining the critical behavior of the multipolar nematic order parameter, we show that it drives the thermal phase transition near 200 K in Cd$_2$Re$_2$O$_7$ and induces a parity-breaking lattice distortion as a secondary order parameter. [Preview Abstract] |
Monday, March 13, 2017 11:27AM - 11:39AM |
B37b.00002: Ergodicity and symmetry breaking in disordered spin chains with non-Abelian on-site symmetry. Abhishodh Prakash, Sriram Ganeshan, Lukasz Fidkowski, Tzu-Chieh Wei We study the eigenstate phasesÂ of disordered spin chains with on-site non-Abelian symmetry. We develop a general formalism based on standard results from group theory to construct local spin Hamiltonians invariant under any on-site symmetry. We then specialize to the case of the simplest non-Abelian group, $S_3$, and numerically study a particular two parameter spin-1 Hamiltonian. Within the accuracy of our numerical analysis, we observe three distinct regions in the two-parameter space of our Hamiltonian. These are distinguished by different behaviors of the entanglement scaling of eigenvectors, their violation or not of the eigenstate thermalization hypothesis (ETH), as well as the Edwards-Anderson like order parameter. These regions are consistent with three possible phases listed by Potter et al.[arxiv:1605.03601] namely thermal/ ergodic, many body localized (MBL) and quantum critical glass (QCG) phases. Nevertheless, we cannot rule out finite size quantum critical cone like effects, especially in the QCG-like region. [Preview Abstract] |
Monday, March 13, 2017 11:39AM - 11:51AM |
B37b.00003: Numerical time evolution of ETH spin chains by means of matrix product density operators Christopher White, Michael Zaletel, Roger Mong, Gil Refael We introduce a method for approximating density operators of 1D systems that, when combined with a standard framework for time evolution (TEBD), makes possible simulation of the dynamics of strongly thermalizing systems to arbitrary times. We demonstrate that the method works on both near-equilibrium initial states (Gibbs states with spatially varying temperatures) and far-from-equilibrium initial states, including quenches across phase transitions and pure states. [Preview Abstract] |
Monday, March 13, 2017 11:51AM - 12:03PM |
B37b.00004: Spin density wave order, topological order, and Fermi surface reconstruction Subir Sachdev, Erez Berg, Shubhayu Chatterjee, Yoni Schattner In the conventional theory of density wave ordering in metals, the onset of spin density wave (SDW) order co-incides with the reconstruction of the Fermi surfaces into small `pockets'. We present models which display this transition, while also displaying an alternative route between these phases via an intermediate phase with topological order, no broken symmetry, and pocket Fermi surfaces. The models involve coupling emergent gauge fields to a fractionalized SDW order, but retain the canonical electron operator in the underlying Hamiltonian. We establish an intimate connection between the suppression of certain defects in the SDW order, and the presence of Fermi surface sizes distinct from the Luttinger value in Fermi liquids. We discuss the relevance of such models to the physics of the hole-doped cuprates near optimal doping. [Preview Abstract] |
Monday, March 13, 2017 12:03PM - 12:15PM |
B37b.00005: Competition between magnetism and superconductivity in Eu-based intermetallic compounds Macy Stavinoha, Lance Green, Julia Chan, Emilia Morosan Eu-based intermetallic compounds present a path to discover new correlated electronic behavior in quantum materials. Reports of superconductivity, intermediate valence behavior, and heavy fermions indicate that Eu-based compounds are promising routes to study the relationship between crystallography and electronic properties. The present work is focused on EuGa$_4$, an antiferromagnet with T$_N$ = 16 K isostructural with the tetragonal RT$_2$M$_2$ (R = rare earth, T = transition metal, M = metal or metalloid) family that exhibits heavy fermion behavior and unconventional superconductivity. Single crystals of the doped series (Eu$_{1-x}$La$_x$)Ga$_4$, (Eu$_{1-x}$Ca$_x$)Ga$_4$, and Eu(Ga$_{1-x}$Al$_x$)$_4$ have been grown using the self-flux method and tested for change in unit cell volume and magnetic susceptibility. Results show that doping with Ca (isoelectronic doping) and La (hole doping) reduce T$_N$ to 12.4 K and 2.3 K, respectively, for Ca doping up to x = 0.11 and La doping up to x = 0.74 without an associated change in unit cell volume. The series Eu(Ga$_{1-x}$Al$_x$)$_4$ has shown incommensurate-to-commensurate magnetic transitions. Future studies will aim to further decrease T$_N$ and the unit cell volume using physical pressure and chemical pressure through doping. [Preview Abstract] |
Monday, March 13, 2017 12:15PM - 12:27PM |
B37b.00006: Single crystal x-ray structure studies of multiferroic CuBr2 near its N\'eel transition Stella Sun, Sangjun Lee, Gilberto De La Pena Munoz, Biaoyan Hu, Yuan Li, Peter Abbamonte CuCl$_{2}$ was the first reported multiferroic in the halogen family\footnote{S. Seki et al.,\textbf{Phys. Rev. B} 82, 064424 (2010)}. CuBr$_{2}$ was later reported to be a multiferroic in the same family, but with a high transition temperature, T$_{N}$ = 73.5K\footnote{L. Zhao et al.,\textbf{Adv. Mat.} 24, 2469-2473 (2012)}. Although it has been reported to have spontaneous spin-driven ferroelectricity according to its polarization data, the reported temperature dependence of the dielectric constant lacks a sharp peak when crossing T$_{N}$, as is observed in CuCl$_{2}$. In order to probe the ionic displacements that are the origin of ferroelectricity in these materials, we performed hard X-ray diffraction studies of CuBr$_{2}$ as a function of temperature through T$_{N}$. Our data reveal no change in the lattice periodicity, however a change in the symmetry of the unit cell is clearly observed in the variation of the Bragg peak intensities with temperature. We will discuss the implications of these structure changes for the mechanism behind the magnetoelectric properties of CuBr$_{2}$. [Preview Abstract] |
Monday, March 13, 2017 12:27PM - 12:39PM |
B37b.00007: Signatures of the Mott transition in the antiferromagnetic state of the two-dimensional Hubbard model Lorenzo Fratino, Patrick Semon, Maxime Charlebois, Giovanni Sordi, A.-M. S. Tremblay The properties of a broken-symmetry phase can be strongly influenced by the underlying normal state. Here we study the two-dimensional Hubbard model using cellular dynamical mean-field theory with continuous-time quantum Monte Carlo to map out the N\'eel state as a function of interaction $U$ and temperature. We link a sharp change between weakly and strongly correlated antiferromagnetism to the underlying Mott metal-insulator transition at intermediate $U$. This result is based on a comparison of the values taken by the potential energy and the local density of states in the two phases, normal and antiferromagnetic. [Preview Abstract] |
Monday, March 13, 2017 12:39PM - 12:51PM |
B37b.00008: Entanglement Entropy for Quantum Phases of Extended Hubbard Model Jon Spalding, Shan-Wen Tsai Evidence has shown the existence of a subtle bond order wave (BOW) phase separating the spin density wave (SDW) and charge density wave (CDW) phases of the insulating extended Hubbard model in one dimension at half filling. Due to the quantum nature of the phase transitions, prior efforts to establish the phase diagram have relied on a-priori defined order parameters. However, recent works have demonstrated that the two-site Von Neumann Entanglement entropy may be a ``one-size-fits-all" way of observing quantum phase transitions, including the Berezinskii-Kosterlitz-Thouless transition that appears in the extended Hubbard model. We calculate this observable with DMRG to update the phase diagram of the extended Hubbard model including the tricritical point and weak-coupling limit. [Preview Abstract] |
Monday, March 13, 2017 12:51PM - 1:03PM |
B37b.00009: Gutzwiller quantum molecular dynamics simulations of Anderson impurity model Jun Liu, Kipton Barros, Joel Kress, Cristian Batista, Gabriel Kotliar, Gia-Wei Chern Molecular dynamics (MD) simulations are crucial to modern computational physics, chemistry, and materials science. We present a formulation of tight-binding quantum molecular dynamics that includes electron correlation effects via the Gutzwiller method. In contrast to the conventional mean-field treatment of the intra-atomic Coulomb repulsion, the Gutzwiller approach captures the crucial correlation effects such as electron localization transition. We perform Gutzwiller quantum MD simulations on the Anderson impurity model and investigate how strong electron correlation affects the structural and dynamical properties of the atoms. [Preview Abstract] |
Monday, March 13, 2017 1:03PM - 1:15PM |
B37b.00010: Predicting Hidden bulk phases in Sr$_3$Ru$_2$O$_7$ from surface phases Pablo Rivero, Chen Chen, Roying Jin, Vincent Meunier, E. W. Plummer, William Shelton Double-layered Sr$_3$Ru$_2$O$_7$ has received phenomenal attention as it exhibits an overabundance of exotic phases when perturbed. Recently it has been shown that the surface of this material displays significantly different properties than in the bulk due to the surface induced tilt of the RuO$_6$ octahedra [1]. Here we report detailed first principles calculations of the surface structure, and the structure property relationship. Tilt of the octahedra drive the surface into a much less conducting state than in the bulk due in part to the different electronic properties of the two Ru atoms in the first RuO$_2$ layer of the bilayer. The broken symmetry at the surface causes a tilt and enhanced rotation of the octahedra only present in the first (surface) bilayer. Theoretically the surface is ferromagnetically ordered but the stability with respect to the antiferromagnetic phase is small ($\simeq$ 11 meV). We have calculated the bulk properties under uniaxial pressure, which induces a tilt and drives the bulk into an antiferromagnetic-insulating state. [1] C. Chen, W. Chen, J. Kim, V. B. Nascimento, Z. Diao, J. Teng, Biao Hu, Guorong Li, Fangyang Liu, Jiandi Zhang, Rongying Jin, and E. W. Plummer, Phys. Rev. B 94, 085420 (2016). [Preview Abstract] |
Monday, March 13, 2017 1:15PM - 1:27PM |
B37b.00011: Machine Learning Phases of Strongly Correlated Fermions Kelvin Chng, Juan Carrasquilla, Roger Melko, Ehsan Khatami Machine learning offers an unprecedented perspective for the problem of classifying phases in condensed matter physics. We employ neural network machine learning techniques to distinguish finite-temperature phases of the strongly-correlated fermions on cubic lattices [1]. We show that a three-dimensional convolutional network trained on auxiliary field configurations produced by quantum Monte Carlo simulations of the Hubbard model can correctly predict the magnetic phase diagram of the model at the average density of one (half filling). We then use the network, trained at half filling, to explore the trend in the transition temperature as the system is doped away from half filling. This transfer learning approach predicts that the instability to the magnetic phase extends to this region, albeit with a transition temperature that falls rapidly as a function of doping. Our results pave the way for other machine learning applications in correlated quantum many-body systems. [1] K. Ch'ng, J. Carrasquilla, R. G. Melko, E. Khatami, cond-mat/arXiv:1609.02552 [Preview Abstract] |
Monday, March 13, 2017 1:27PM - 1:39PM |
B37b.00012: Controlled evidence for phase separation in the fermionic 2D Hubbard model Fedor \v{S}imkovic, Evgeny Kozik, Boris Svistunov, Nikolay Prokof'ev, Youjin Deng In this study we inspect the repulsive two-dimensional fermionic Hubbard model at doping values $0.6\le n \le 1$ and moderate interaction strength $U=4$ by means of the Bold Diagrammatic Monte Carlo \footnote{Y. Deng et al. Europhysics Letters {\bf 110(5)}, 57001, (2015) }(DiagMC) and Determinant Diagrammatic Monte Carlo \footnote{E. Burowski et al. New Journal of Physics {\bf 8}, 153, (2006) }(DDMC). We use a stability condition for the inverse compressibility to prove in a controlled and unbiased way the existence of a first order phase transition and intermediate phase separated region between the $d_{x^2-y^2}$-wave superfluid at densities $n<0.8$ and the anti-ferromagnetic phase at half filling ($n=1.0$). The critical density of $n_c \sim 0.82$ obtained via Maxwell construction is in good correspondence with the region of densities where magnetic fluctuations become significant at $U=4$. [Preview Abstract] |
Monday, March 13, 2017 1:39PM - 1:51PM |
B37b.00013: Strongly Interacting Phases of Metallic Wires in Strong Magnetic Field Daniel Bulmash, Chao-Ming Jian, Xiao-Liang Qi We elucidate the phase diagram of an interacting, thick metallic wire in a strong magnetic field directed along its length. By considering a suitable change in spatial geometry, we map the problem in the zeroth Landau level with Landau level degeneracy $N$ to one-dimensional fermions with an $N$-component pseudospin degree of freedom and $SU(2)$-symmetric interactions. This mapping allows us to establish the phase diagram as a function of the interactions for small $N$ (and make conjectures for large $N$) using renormalization group and non-Abelian bosonization techniques. We find pseudospin-charge separation with a gapless $U(1)$ charge sector and several possible strong-coupling phases in the pseudospin sector. For odd $N$, we find a fluctuating pseudospin-singlet charge density wave phase and a fluctuating pseudospin-singlet superconducting phase which are topologically distinct. For even $N>2$, the same phases exist, although they are not topologically distinct, and an additional pseudospin-gapless phase appears. We also make conjectures about topological obstructions to certain ways of gapping out certain Wess-Zumino-Witten models. [Preview Abstract] |
Monday, March 13, 2017 1:51PM - 2:03PM |
B37b.00014: Characterization of first-order phase transitions in ion-irradiated materials Juan Trastoy, Yoav Kalcheim, Javier del Valle, Sheena Patel, Jean-Paul Crocombette, Eric E. Fullerton, Dafine Ravelosona, Javier E. Villegas, Ivan K. Schuller First-order phase transitions englobe abrupt changes in very diverse properties (electronic, structural, magnetic, etc) and are among the most commonly studied phenomena in condensed matter physics. However, in cases like Mott transitions the responsible mechanism has not been clearly stablished. We have fabricated via sputtering deposition Mott-insulating VO2 and V2O3 films, as well as FeRh films. The three materials exhibit first-order electronic and structural phase transitions, in addition to a magnetic transition in the cases of V2O3 and FeRh. In order to gain insight into the mechanisms involved, we have induced defects in the materials through ion irradiation and studied the effects in the phase transitions as well as physical properties like the number of carriers and the electron mobility. [Preview Abstract] |
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