Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session S22: Strong Correlations in Low Dimensional Systems |
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Sponsoring Units: DCMP Room: 202A |
Thursday, March 5, 2015 8:00AM - 8:12AM |
S22.00001: Room-Temperature Studies of Li$_{0.9}$Mo$_{6}$O$_{17}$ by Scanning Tunneling Microscopy Michael Boyer, Ling Fu, Aaron Kraft, Martha Greenblatt The lithium purple bronze (Li$_{0.9}$Mo$_{6}$O$_{17}$) is a quasi-1 dimensional material as evidenced by high anisotropy in resistivity and thermal conductivity measurements. The material has garnered interest due to experimental evidence for Luttinger Liquid physics from 25 K to 300 K. Here we present our room-temperature topographic and spectroscopic scanning tunneling microscopy measurements on Li$_{0.9}$Mo$_{6}$O$_{17}$. We interpret the observed topographic and spectroscopic features in the context of previous bulk and surface measurements as well as theoretical models describing the 1-dimensional physics of the lithium purple bronze. [Preview Abstract] |
Thursday, March 5, 2015 8:12AM - 8:24AM |
S22.00002: Thermoelectric effects in the field-suppressed superconducting state of quasi-one-dimensional Li$_{0.9}$Mo$_6$O$_{17}$ Joshua L. Cohn, Carlos A.M. dos Santos, John J. Neumeier We present resistivity, thermopower ($S$), and Nernst ($\nu$) measurements in the range $0.4~K\leq T\leq 20$~K on single crystals of the quasi-one-dimensional (q1D) metal, Li$_{0.9}$Mo$_6$O$_{17}$ (LiPB) along the q1D metallic chains. The low-$T$ limits of $S/T$ and $\nu/T$, determined in the magnetic-field suppressed superconducting state ($T_c=2$~K), indicate a very small Fermi temperature ($T_F\sim 30$~K), contrary to expectations from prior work including photoemission. Possible insights from these results into the nature of the mysterious density-wave order\footnote{C. A. M. dos Santos {\it et al.}, Phys. Rev. Lett. {\bf 98}, 266405 (2007).}$^,$\footnote{X. Xu \emph{et al.}, Phys. Rev. Lett. {\bf 102}, 206602 (2009).} responsible for the upturn in resistivity below $\sim 25$~K will be discussed. [Preview Abstract] |
Thursday, March 5, 2015 8:24AM - 8:36AM |
S22.00003: Topological character and chiral solitons in double Peierls-distorted chains Sangmo Cheon, Tae-Hwan Kim, Sung-Hoon Lee, Han Woong Yeom Chiral edge states have played an important role in understanding condensed matter systems such as quantum Hall systems and topological insulators. In 1D electronic systems, Peierls-distorted atomic chains such as polyacetylene have two topologically different ground states and thus have topological edge states between them. The edge states---topological solitons---show novel properties of charge-spin separation and fractional charge. Here, we present theoretical results on the topological properties of double Peierls-distorted chains with interchain coupling. The double Peierls chains support a dynamically generated topological structure with four-fold symmetric ground states and have topological solitons with a new degree of freedom, chirality, which is absent in a single chain. We also discuss experimental evidence of the chiral solitons in the 1D charge-density wave (CDW) system of indium atomic nanowires on silicon substrates. [Preview Abstract] |
Thursday, March 5, 2015 8:36AM - 8:48AM |
S22.00004: Photoinduced Dynamics of Charge Density Waves in Mott-Peierls Systems Yao Wang, Cheng-Chien Chen, Chunjing Jia, Michel van Veenendaal, Thomas Devereaux, Brian Moritz Studying non-equilibrium dynamics can potentially enhance our understanding of the physics underlying competing orders in strongly correlated systems. To characterize charge-ordered systems in time-resolved pump-probe experiments, we examine the photoinduced dynamics of charge and spin density waves in one-dimensional Mott-Peierls systems, by exact diagonalization and Krylov time-evolution techniques. We observe anti-phase dynamics at the renormalized phonon frequency and a coupling-strength-dependent suppression/enhancement of CDW/SDW orders, reflecting the competing-order-driven phase transition. Our study offers an approach to analyze and classify competing or coexisting orders in strong correlated systems through non-equilibrium dynamics. [Preview Abstract] |
Thursday, March 5, 2015 8:48AM - 9:00AM |
S22.00005: Photodynamics of optical excitations in one-dimensional models for organic salts. Julian Rincon, Khaled Al-Hassanieh, Adrian Feiguin, Elbio Dagotto We study the time-dependent evolution of photogenerated optical excitations in a model for organic salts, using the density matrix renormalization group method. The model consists of the quarter-filled one-dimensional extended Peierls-Hubbard Hamiltonian interacting with a classical time-dependent electric field. Our main results show that the overall dynamics of the dominating 4$k_{F}$ bond and charge instabilities corresponds to a gigantic fluctuating behavior as a function of time, whereas the 2$k_{F}$ state remains largely unaffected. These results remain valid regardless of the nature of the optical excitations and whether the system is driven resonantly or not. We compare our calculations with experimental pump-and-probe ultrafast spectroscopy studies of the optical conductivity in organic compounds. [Preview Abstract] |
Thursday, March 5, 2015 9:00AM - 9:12AM |
S22.00006: Bond patterns in 1/4-filled spin-Peierls materials Andrew Ward, R. Torsten Clay, Niladri Gomes, Sumit Mazumdar In the 1/4-filled quasi-one dimensional molecular charge transfer solids (CTS) there exist two distinct classes of spin-Peierls (SP) transitions. The two classes are distinguished by differing bond patterns: either the pattern Strong-Medium-Weak-Medium (SMWM), or the pattern Strong-Weak-Strong-Weak' (SWSW'). Experimentally the SP transition temperature of CTS of the first type (SMWM) is much higher than those of the second type (SWSW'). This indicates that the small change in bond patterns within the SP phase greatly affects the electronic behavior of the CTS. We show that these two bond patterns can be explained within the one dimensional Extended Hubbard Model. We use quantum Monte Carlo and finite-size scaling to create a phase diagram for the 1/4-filled 1D CTS and discuss charge order amplitude and other experimental observables. [Preview Abstract] |
Thursday, March 5, 2015 9:12AM - 9:24AM |
S22.00007: Charge fluctuations in the metallic phase of Lithium purple bronze Jose Alvarez, Jaime Merino, Natalia Lera We study the role of charge fluctuations for a model of the quasi-one-dimensional Li$_{0.9}$Mo$_6$O$_{17}$ and study their influence in ARPES experiments. Coulomb repulsion induces a charge ordering (CO) transition in a multiorbital extended Hubbard model. The ordering pattern is different from the one present in a conventional CDW driven by Fermi surface nesting. We assume that purple bronze lays in the metallic side of this phase diagram, but still very close to the CO transition. In these regime, strong charge fluctuations manifest themselves through low-energy collective excitations softening in the proximity the transition, which may be directly visible in HRIX experiments. We discuss specific role of quasi-one-dimensionality in this context. We argue that the electronic scattering by these charge fluctuations can lead to the upturn in the resistivity observed at 24K and the deviations of scaling observed in ARPES . [Preview Abstract] |
Thursday, March 5, 2015 9:24AM - 9:36AM |
S22.00008: Local correlation effects on pyrochlore iridate thin films in [111] direction Qi Chen, Hsiang-Hsuan Hung, Xiang Hu, Gregory A. Fiete We study the local correlation effects on topological phases of matter in pyrochlore oxide thin films of the form $A_2 B_2 O_7$ oriented along the $[111]$ direction. We examine bilayer and trilayer lattice models, including an on-site Hubbard interaction, by cellular dynamical mean field theory. The local correlation effects on the topological and magnetic phases are explored in both thin film geometries. Our focus is on the stability of the interaction induced Chern Insulator phases found in mean-field (Hartree-Fock) studies. By including dynamical fluctuations and computing the topological invariants from the single-particle Greens function, we corroborate the results of the Hartree-Fock mean field study and point out the differences. We discuss the likelihood of the Chern insulator phase being experimentally realized in transition metal oxide thin films. [Preview Abstract] |
Thursday, March 5, 2015 9:36AM - 9:48AM |
S22.00009: Perfect Metal Phases of One-Dimensional and Anisotropic Higher-Dimensional Systems Eugeniu Plamadeala, Michael Mulligan, Chetan Nayak We show that a 1D quantum wire with $23$ channels of interacting fermions has a perfect metal phase in which all weak perturbations that could destabilize this phase are irrelevant. Consequently, weak disorder does not localize it, a weak periodic potential does not open a gap, and contact with a superconductor also fails to open a gap. Similar phases occur for $N \geq 24$ channels of fermions, except for $N=25$, and for $8k$ channels of interacting bosons, with $k\geq 3$. Arrays of perfect metallic wires form higher-dimensional fermionic or bosonic perfect metals, albeit highly-anisotropic ones. [Preview Abstract] |
Thursday, March 5, 2015 9:48AM - 10:00AM |
S22.00010: Observation of a hierarchy of modes in an interacting one-dimensional system Christopher Ford, Maria Moreno, Yiqing Jin, Wooi Kiat Tan, Jon Griffiths, Ian Farrer, Geb Jones, Anne Anthore, David Ritchie, Oleksandr Tsyplyatyev, Andrew Schofield Studying interacting fermions in 1D at high energy, we find a hierarchy in the spectral weights of the excitations theoretically and we observe evidence for second-level excitations experimentally. Diagonalising a model of fermions (without spin), we show that levels of the hierarchy are separated by powers of $\mathcal{R}^{2}/L^{2}$, where $\mathcal{R}$ is a length-scale related to interactions and $L$ is the system length. The first-level (strongest) excitations form a mode with parabolic dispersion, like that of a renormalised single particle. The second-level excitations produce a singular power-law line shape to the first-level mode and multiple power-laws at the spectral edge. We measure momentum-resolved tunneling of electrons (fermions with spin) from/to a wire formed within a GaAs heterostructure, which shows parabolic dispersion of the first-level mode and well-resolved spin-charge separation at low energy with appreciable interaction strength. We find structure resembling the second-level excitations, which dies away quite rapidly at high momentum. [Preview Abstract] |
Thursday, March 5, 2015 10:00AM - 10:12AM |
S22.00011: Dynamics of hot random quantum spin chains: from anyons to Heisenberg spins Siddharth Parameswaran, Andrew Potter, Romain Vasseur We argue that the dynamics of the random-bond Heisenberg spin chain are ergodic at infinite temperature, in contrast to the many-body localized behavior seen in its random-field counterpart. First, we show that excited-state real-space renormalization group (RSRG-X) techniques suffer from a fatal breakdown of perturbation theory due to the proliferation of large effective spins that grow without bound. We repair this problem by deforming the $SU(2)$ symmetry of the Heisenberg chain to its `anyonic' version, $SU(2)_k$, where the growth of effective spins is truncated at spin $S=k/2$. This enables us to construct a self-consistent RSRG-X scheme that is particularly simple at infinite temperature. Solving the flow equations, we compute the excited-state entanglement and show that it crosses over from volume-law to logarithmic scaling at a length scale $\xi_k \sim e^{\alpha k^3}$. This reveals that (a) anyon chains have random-singlet-like excited states for any finite $k$; and (b) ergodicity is restored in the Heisenberg limit $k\rightarrow\infty$. [Preview Abstract] |
Thursday, March 5, 2015 10:12AM - 10:24AM |
S22.00012: ABSTRACT WITHDRAWN |
Thursday, March 5, 2015 10:24AM - 10:36AM |
S22.00013: Properties of a One-Dimensional Dirac Liquid Matthew Gochan, James Stokes, Kevin Bedell Recent experimental results, as well as technological implications, have lead to a resurgence in the analysis of one-dimensional systems. Of particular interest are the technological advances possible in one-dimensional systems; specifically carbon nano-tubes and nano-wires. Here we investigate the properties of a one-dimensional Dirac liquid. We show a distinct change in the behavior of the exponents of quantities such as the correlation functions, density of states, and momentum distribution function. We find that these exponents, as well as relevant thermodynamic and transport properties are independent of density. Additionally, we discuss the consequences the Virial Theorem has on such systems. [Preview Abstract] |
Thursday, March 5, 2015 10:36AM - 10:48AM |
S22.00014: Transport across two interacting quantum dots: Bulk Kondo, Kondo box, and molecular regimes Laercio Costa Ribeiro, Ignacio Hamad, Guillermo Chiappe, Enrique Victoriano Anda We analyze the transport properties of a double quantum dot device with both dots coupled to perfect conducting leads and to a finite chain of N noninteracting sites connecting both of them. The interdot chain strongly influences the transport across the system and the local density of states of the dots. We study the case of a small number of sites, so that Kondo box effects are present, varying the coupling between the dots and the chain. For odd N and small coupling between the interdot chain and the dots, a state with two coexisting Kondo regimes develops: the bulk Kondo due to the quantum dots connected to leads and the one produced by the screening of the quantum dot spins by the spin in the finite chain at the Fermi level. As the coupling to the interdot chain increases, there is a crossover to a molecular Kondo effect, due to the screening of the molecule (formed by the finite chain and the quantum dots) spin by the leads. For even N the two Kondo temperatures regime does not develop and the physics is dominated by the usual competition between Kondo and antiferromagnetism between the quantum dots. [Preview Abstract] |
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