Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session V16: Correlated Electrons: Luttinger Liquids, Ladders, and Charge Ordered Systems |
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Sponsoring Units: GMAG Chair: Noah Bray Ali, University of Southern California Room: Colorado Convention Center Korbel 4F |
Thursday, March 8, 2007 11:15AM - 11:27AM |
V16.00001: Much Ado about Zeros: The Luttinger Surface and Mottness Philip Phillips, Tudor Stanescu, Ting-Pong Choy We prove that the Mott insulating state is characterized by a divergence of the electron self energy at well-defined values of momenta in the first Brillouin zone. When particle-hole symmetry is present, the divergence obtains at the momenta of the Fermi surface for the corresponding non-interacting system. Such a divergence gives rise to a surface of zeros (the Luttinger surface) of the single-particle Green function and offers a single unifying principle of Mottness from which pseudogap phenomena, spectral weight transfer, and broad spectral features emerge in doped Mott insulators. We also show that only when particle-hole symmetry is present does the volume of the zero surface equal the particle density. We identify that the general breakdown of Luttinger's theorem in a Mott insulator arises from the breakdown of a perturbative expansion for the self energy in the single-particle Green function around the non-interacting limit. A modified version of Luttinger's theorem is derived for special cases. [Preview Abstract] |
Thursday, March 8, 2007 11:27AM - 11:39AM |
V16.00002: Theory of STM Spectroscopy in Luttinger Liquids with a Spin Gap Akbar Jaefari, Eduardo Fradkin We discuss the problem of tunneling of electrons into a Luttinger liquid with a spin gap for a semi infinite one-dimensional system. This system is of interest for a problem of STM spectroscopy of a spin-gap Luttinger liquid with a backscattering impurity. We will discuss this problem using semi-classical and refermionization methods. [Preview Abstract] |
Thursday, March 8, 2007 11:39AM - 11:51AM |
V16.00003: A finite Luttinger liquid with longer range interactions Imke Schneider, Sebastian Eggert, Alexander Struck We consider the bosonization of a finite quantum wire with longer range interactions. In order to use the Luttinger liquid formalism it is necessary to introduce a changing effective interaction parameter as a function of momentum. We show that it is possible to modify the formalism so that the electron distribution in individual states can be analyzed with help of a recursive formula. Quantitative predictions for the local density of states and STM experiments can be made. In limiting cases the well known power laws are recovered. We compare the calculations with DMRG simulations of the spin $\frac{1}{2}$ Heisenberg chain. [Preview Abstract] |
Thursday, March 8, 2007 11:51AM - 12:03PM |
V16.00004: Possible Dimensional Crossover in Li$_{0.9}$Mo$_6$O$_{17}$ observed through Thermal Expansion Experiments Carlos A. M. dos Santos, B. D. White, Y.-K. Yu, J. J. Neumeier, J. A. Souza During recent years much attention has been given to Li$_{0.9}$Mo$_6$O$_{17}$ which is believed to be the best-known example of a Luttinger-liquid (LL). In order to study the thermal expansion behavior of this compound prepared single crystals via flux growth using Li$_2$MoO$_4$, MoO$_2$ and MoO$_3$. The crystals were mechanically, chemically separated and characterized by x-ray and Laue diffraction, and electrical resistance. Thermal expansion measurements performed with a high-resolution quartz dilatometer revealed high anisotropy. Dominant a-axis thermal expansion reduces the separation of the conducting zigzag chains enhancing the interchain coupling. This is argued to destabilize the LL leading to a crossover from metallic to insulating-like behavior near 28 K and a repulsion-induced CDW. Competing electron-electron interactions support superconductivity at 1.9 K. [Preview Abstract] |
Thursday, March 8, 2007 12:03PM - 12:15PM |
V16.00005: Electrical Transport Properties of the Purple Bronze Li$_{0.9}$Mo$_6$O$_{17}$ Mario S. da Luz, Jamy Moreno, C. A. M. dos Santos, B. D. White, J. A. Souza, J. J. Neumeier The crossover from metallic to semiconductor-like behavior in Li$_{0.9}$Mo$_6$O$_{17}$ has been the subject of intense discussion. An important issue is whether or not it is a Luttinger Liquid. This idea has received substantial support because of the quasi-one dimensionality observed in electrical resistivity measurements performed 20 years ago. In this work the transport properties of Li$_{0.9}$Mo$_6$O$_{17}$ single crystals are revisited. Crystals were characterized by x-ray powder diffractometry and the crystallographic orientations were determined by transmitted Laue diffraction. Electrical resistance as a function of temperature, $R(T)$, performed using standard four probe and Montgomery methods are compared. The magnetic field dependence of the minimum in the $R(T)$ curves and the temperature dependence of the insulating-like regime are also presented. [Preview Abstract] |
Thursday, March 8, 2007 12:15PM - 12:27PM |
V16.00006: Ground state properties of quasi-1D systems Kenneth Graham, Samuel Moukouri We use the two-step density-matrix renormalization group method to study the competition between an antiferromagnet and superconductivity. We find that in the absence of frustration the ground state is dominated by antiferromagnetic fluctuations. In the presence of frustration the antiferromagnetism is reduced but we don't find a significant pairing tendency. [Preview Abstract] |
Thursday, March 8, 2007 12:27PM - 12:39PM |
V16.00007: Binding of spinon and holon in the anisotropic 1D $t-J$ model Jurij Smakov, Alexander Chernyshev, Steven White In the 1D $t-J$ and Hubbard models spin and charge dynamics are independent, leading to the well-known spin-charge separation: splitting of the physical electron (hole) into free spinon and holon excitations. Considerably less is known about the interaction between such excitations. To address this problem, we have performed a detailed theoretical and numerical study of anisotropic $XXZ$-version of the $t$-$J$ model using Bethe-Salpeter equation and exact diagonalization and DMRG methods on systems of up to 128 sites. We find that holon and spinon form a bound state for any value of anisotropy $\alpha=J_\perp/J_z$ smaller than one. A remarkable agreement between the theory and numerical results has been demonstrated. We argue that the binding is largely controlled by the spinon energy spectrum. Qualitatively, the bound state near the Ising limit $\alpha\ll 1$ corresponds to the confinement of a free holon in the vicinity of an essentially immobile, impurity-like spinon with binding energy $\Delta \sim J_z^2/t$. However, already for $\alpha\agt 0.5$ an almost relativistic spinon is only weakly bound to the holon. Such a change in the character of pairing results in a dramatic evolution of $\Delta$ as a function of $\alpha$: binding energy goes from a finite value at $\alpha=0$ to the exponential drop-off close to the isotropic case. [Preview Abstract] |
Thursday, March 8, 2007 12:39PM - 12:51PM |
V16.00008: Probing the pairing symmetry and pair charge stiffness of doped $t-J$ ladders: a DMRG study Adrian E. Feiguin, S. R. White, D. J. Scalapino We perform the numerical equivalent of a phase sensitive experiment on $t-J$ ladders. We apply proximity effect fields with different complex phases at both ends of an open system and we study the transport of Cooper pairs. Measuring the response of the system and the induced Josephson current, Density Matrix Renormalization Group calculations show how, depending on the doping fraction, the rung-leg parity of the pair field changes from minus to plus as the density of holes is increased. We also study the pair charge stiffness. [Preview Abstract] |
Thursday, March 8, 2007 12:51PM - 1:03PM |
V16.00009: Hole Dynamics in a 2D Striped-Ordered Quantum Antiferromagnet Satyaki Kar, Efstratios Manousakis We study the single hole motion in a $2D$ quantum antiferromagnet in a stripe background within the $t-J$ model, using an additional ferromagnetic term along the domain walls to stabilize the stripes. The spin wave approximation is used to linearize the Hamiltonian and we calculate the different flavors of spin-wave dispersions and hole propagators by means of a self consistent perturbation scheme within the non-crossing approximation. The hole spectral functions will be compared to the experimental ARPES data available for $La_{2-x}Sr_{x}CuO_{4}$ and concentration of $x=\frac{1}{8}$. [Preview Abstract] |
Thursday, March 8, 2007 1:03PM - 1:15PM |
V16.00010: Charge dynamics in an incommensurate layered cuprate $Sr_{14}Cu_{24}O_{41}$ : A momentum-resolved study Lewis Wray, Dong Qian, David Hsieh, Matthew Xia, Hiroshi Eisaki, Zahid Hasan We report the first \textit{momentum resolved} charge mode spectrum of insulating $Sr_{14}Cu_{24}O_{41}$ using inelastic resonant x-ray scattering. Our results show that the intense excitation modes at the charge gap edge predominantly originate from the ladder-containing two-dimensional planes. The observed modes (E vs. Q) are found to be dispersive for momentum transfers along the ``legs'' ($\vec{Q}$ $\parallel$ $\hat{c}$) but nearly localized along the ``rungs'' ($\vec{Q}$ $\parallel$ $\hat{a}$). Dispersion and peakwidth characteristics are strongly similar to the low energy charge spectrum of quasi-one dimensional $SrCuO_2$, and we suggest a qualitative explanation in terms of a model in the strongly correlated limit ($U\gg t$). This behavior is in marked contrast to the charge spectrum observed in most two dimensional cuprates. Quite generally, our results also show that momentum-tunability of inelastic scattering can be used to resolve mode contributions in multi-component correlated systems. [Preview Abstract] |
Thursday, March 8, 2007 1:15PM - 1:27PM |
V16.00011: Pressure effect on the charge-density-wave order in pure and doped (La,R)AgSb$_2$ (R = Ce, Nd) compounds M.S. Torikachvili, S.L. Bud'ko, S.A. Law, M.E. Tillman, E.D. Mun, P.C. Canfield We studied the pressure dependent resistivity, $\rho(T)$, of single-crystals of pure and doped (La,R)AgSb$_2$ (R = Ce, Nd) compounds, up to 23 kbar, for temperatures $2 \leq T \leq 300$ K. LaAgSb$_2$ displays features at $T_1 = 210$ K, and $T_2 = 185$ K, due to the formation of charge-density-wave (CDW) order along the $a-$ and $c-$ axis of the tetragonal structure, respectively. The effect of pressure in LaAgSb$_2$ is to lower $T_1$ at the rate of -4.5 K/kbar. Partial substitutions of Nd and Ce for La depress $T_1$ as well, and the effect of pressure is to lower it further. The value of $T_1 = 112$ K for La$_{0.75}$Nd$_{0.25}$AgSb$_2$ drops with pressure at the rate of -5.8 K/kbar, until the feature in $\rho(T)$ cannot be identified above 12 kbar, suggesting the closure of the CDW gap. The effect of pressure on La$_{0.9} $Ce$_{0.1}$AgSb$_2$, and La$_{0.8}$Ce$_{0.2}$AgSb$_2$ is to depress $T_1$ at the rate of $\approx -10$ K/kbar, with the suppression of CDW order for $P \approx 12$ and $\approx 8$ kbar, respectively. The $\rho(T)$ data for the Ce-doped compounds show upturns at low temperatures due to the Kondo effect, and the minimum in $\rho(T)$ is lowered with pressure. [Preview Abstract] |
Thursday, March 8, 2007 1:27PM - 1:39PM |
V16.00012: Bond-stretching phonon mode in stripe ordered orthorhombic $\bf Nd_{1.67}Sr_{0.33}NiO_4$. M. H\"ucker, T. Fukuda, G. D. Gu, J. M. Tranquada, A. Q. R. Baron, J. P. Hill Inelastic x-ray scattering (IXS) experiments on $\rm Nd_{1.67} Sr_{0.33}NiO_4$ have been performed to study electron-phonon interactions in this charge stripe ordered nickelate. Resurgent interest in such phenomena has been triggered by recent results on the high temperature superconductors, where a kink in the electron dispersion as well as striking anomalies in high- energy optical phonon modes have been observed. A significant softening of the bond-stretching-phonon mode for $\rm Q||[100]$ was also observed in the tetragonal nickelate $\rm La_{1.69}Sr_ {0.31}NiO_4$ with inelastic neutron scattering. Moreover, this compound shows an apparent splitting of the bond-stretching mode along the $\rm [110]$ direction. Here we present first IXS results for $\rm Q||[110]$ on the orthorhombic compound $\rm Nd_ {1.67}Sr_{0.33}NiO_4$, which is characterized by domains with unidirectional stripe order. By probing different spots on the sample with different domain distribution, a weak contrast between the phonon spectra has been observed. We discuss these differences in terms of phonons propagating parallel and perpendicular to the stripe direction, as well as the anisotropic, i.e. orthorhombic, lattice structure. [Preview Abstract] |
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