Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session L38: Charge Order in One-Dimensional Systems |
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Sponsoring Units: DCMP Chair: Stuart Brown, University of California, Los Angeles Room: F149 |
Tuesday, March 16, 2010 2:30PM - 2:42PM |
L38.00001: Aharonov-Casher Effect in One-Dimensional Wigner Crystals Yaroslav Tserkovnyak, Markus Kindermann We theoretically study the effects of spin-orbit coupling on spin exchange in a low-density Wigner crystal. In addition to the familiar antiferromagnetic Heisenberg exchange, we find general anisotropic interactions in spin space if the exchange paths allowed by the crystal structure form loops in real space. In particular, it is shown that the two-electron exchange interaction can acquire ferromagnetic character. Tserkovnyak and Kindermann, Phys. Rev. Lett. 102 (2009) 126801. [Preview Abstract] |
Tuesday, March 16, 2010 2:42PM - 2:54PM |
L38.00002: Superconductivity close to a charge-density-wave instability Claude Bourbonnais, Hassan Bakrim The recent discovery of superconductivity (SC) in proximity of a Peierls distorted phase in the perylene based organic conductor Per$_2$Au(mnt)$_2$ [1] has raised once again the issue about the role of charge-density-wave (CDW) correlations in the mechanism of Cooper pairing. We have applied the renormalization group approach to a quasi-1D model of electrons interacting with acoustic phonons modes and studied the interplay between the two instabilities. From the one-loop flow equations for the momentum and frequency dependent interactions induced by phonons we analyze the stability of CDW and SC states {\it vs} the phonon frequency $\omega_D$ and the hopping parameter $t_\perp'$ for nesting alterations. S-wave SC is demonstrated to be stabilyzed above some critical ${t'}^{*}_\perp$. In these conditions, the superconducting $T_c \sim \omega_D^\eta$ exibits a non-BCS power law increase with $\omega_D$($\eta\simeq 0.7$), as a result of quantum interfering CDW and SC pairings. The complete phase diagram is obtained as a function of both $t_\perp'$ and $\omega_D$ and shown to agree with the one found for Per$_2$Au(mnt)$_2$ under pressure [1]. \medskip \par\noindent [1] D. Graf {\it et al.,} Eur. Phys. Lett. {\bf 85}, 27009 (2009). [Preview Abstract] |
Tuesday, March 16, 2010 2:54PM - 3:06PM |
L38.00003: Instability of ferroelectric states induced by coexisting charge orders Maxim Mostovoy, Marcus van der Vegte Ferroelectricity induced by coexisting site-centered and bond-centered charge density waves, was observed in a number of quasi-one-dimensional organic materials, such as TTF-CA and (TMTTF)$_{2}$X. It was also suggested that the interplay between charge, orbital, and spin degrees of freedom in doped manganites results coexisting site- and bond-centered alternations of the electron charge density close to half doping, making these materials ferroelectric. We discuss ferroelectric states induced by coexisting charge density waves from a phenomenological point of view and show that close to ordering transition they are inherently unstable towards an incommensurate modulation of charge density, which breaks the homogeneous states into domains separated by electrically charged domain walls. Our results explain phases observed in doped manganites, vanadium dioxide and other materials. We also present a microscopic model of the incommensurate state in the frustrated spin-Peierls compounds TiOCl and TiOBr. [Preview Abstract] |
Tuesday, March 16, 2010 3:06PM - 3:18PM |
L38.00004: Reversible switching of magnetic transitions in Na$_{x}$CoO$_{2}$ (x $\approx $ 0.83) by altering the Coulomb potential background J. Kanter, Ch. Niedermayer, K. Mattenberger, B. Batlogg In sodium cobaltate the electrons in the CoO$_{2}$ layers are subject to a complex Coulomb potential landscape produced by the adjacent sodium ions which, due to their partial mobility, form various ordering patterns. In recent studies we could reversibly switch between distinct magnetic transitions with a T$_{c}$ of 8 K and 16 K. This was accomplished by preparing different sodium configurations connected to a sodium reordering transition around 280 K. The distinct magnetic phases are investigated by means of muon spin rotation, resistivity, specific heat and magnetization measurements with a focus on the magnetic moment orientation and the dependence of the transition temperatures on the magnetic field strength and orientation. Resistivity measurements under high pressure allow for comparison of the shifts in the transition temperature to the relative change in lattice parameters along the different crystal directions. [Preview Abstract] |
Tuesday, March 16, 2010 3:18PM - 3:30PM |
L38.00005: ABSTRACT WITHDRAWN |
Tuesday, March 16, 2010 3:30PM - 3:42PM |
L38.00006: Charge Disproportionation without Charge Ordering in Organic Conductors Kazuyoshi Yoshimi, Takeo Kato, Hideaki Maebashi Based on a study of a $3/4$-filled extended Hubbard model with an inter-site Coulomb interaction, we show that charge disproportionation is self-generated in the presence of strong charge fluctuations even if there is no charge ordering. In the absence of a frustrating Coulomb interaction, the extended Hubbard model is found to be unstable to phase separation into electron-rich and electron-poor metallic phases near its charge-ordering transition point. By switching on the frustrating Coulomb interaction, this phase separation is transformed into exotic disproportionation such as a stripe glass or a mosaic studed with mesoscale charged droplets. Such disproportionation is a possible origin of extremely slow charge dynamics observed in $\theta $-type BEDT-TTF organic conductors [1,2]. [1] R. Chiba, \textit{et al}. Phys. Rev. Lett \textbf{93}, 216405 (2004). [2] R. Chiba, \textit{et al}. Phys. Rev. B \textbf{77}, 115113 (2008). [Preview Abstract] |
Tuesday, March 16, 2010 3:42PM - 3:54PM |
L38.00007: The Unifided Theory of Angular Magnetic Oscillations in Q1D Conductors Si Wu, Andrei Lebed We develop a unification theory of the angular magnetoresistance oscillations, experimentally observed in quasi-low-dimensional organic conductors. We demonstrate that electron trajectories become extended and interlayer resistance show minima at certain commensurate directions of a magnetic field. We compare our theory with the existing experiments on the Lee-Naughton-Lebed oscillations and the Lebed Magic Angel effects and obtain good qualitative and quantitative agreement between the theory and experimental data. Our work is supported by the NSF through the grant DMR-0705986. [Preview Abstract] |
Tuesday, March 16, 2010 3:54PM - 4:06PM |
L38.00008: Anomalous Hall Resistance jump at Lebed's magic angles Kaya Kobayashi, Taichi Terashima, Shinya Uji, Jun'ichi Yamada, Toshiyuki Mitsui We performed a series of electrical transport measurements focusing on the transverse response (the Hall effect) far from the Field-Induced Spin Density Wave (FISDW) region, and found anomalous enhancement at certain angles. The signal behavior bares similarity to that observed in Nernst effect measurements, though the magnetic field strength and angular region are different. This similarity suggests that the two effects originate from the same mechanism dominated by conduction locked in the plane of the magnetic field at magic angles. We report detailed transport measurements and discuss the conduction mechanism in the vicinity of Lebed's magic angles. [Preview Abstract] |
Tuesday, March 16, 2010 4:06PM - 4:18PM |
L38.00009: NMR investigation on quasi-one-dimensional purple bronze Li$_{0.9}$Mo$_{6}$O$_{17}$ Guoqing Wu, W.G. Clark, S.E. Brown, J.J. Neumeier, C.A.M. dos Santos, J. Marcus, C. Berthier, M. Horvatic $^{7}$Li-NMR measurements are reported for a single crystal of quasi-1D conductor Li$_{0.9}$Mo$_{6}$O$_{17}$ (lithium purple bronze) as a function of temperature ($\it{T}$) and applied magnetic field ($B_{0}$). The $^{7}$Li-NMR spin-lattice relaxation rate (1/$T_{1}$) follows a Korringa relation above $\sim$ 50 K and has surprising features at lower $T$ with 6T$\leq$ B$_{0}$$\leq$12 T. This behavior indicates a conventional electron motion in the high $T$ metallic state with a change at lower $T$ in the electron density of states and perhaps the correlation time. A similar behavior is also shown by $^{95}$Mo 1/$T_{1}$ measurements made at 14.8 T. The $^{7}$Li-NMR spectra also show a significant inhomogeneous broadening and frequency shift across the temperature ($T_{min}$) where the resistivity exhibits a minimum. This indicates a substantial local field change below $T_{min}$. A possible scenario for the development of a field induced spin-density wave state is discussed. Noticeably, these are challenging experiments due to the long $^{7}$Li spin- lattice relaxation time ($T_{1}$) and small natural abundance of $^{95} $Mo in the material. It is the first reported NMR measurement for the material. This work was supported at UCLA by NSF Grants DMR-0334869 and DMR-0520552, and at MSU by NSF Grant DMR-0907036. [Preview Abstract] |
Tuesday, March 16, 2010 4:18PM - 4:30PM |
L38.00010: Single particle gap in Li$_{0.9}$ Mo$_6$ O$_{17}$ below 26K? L. Dudy, J. Park, B.J. Kim, C. Kurdak, J.W. Allen, J. He, R. Jin, D. Mandrus, S. Suga, A. Sekiyama, H. Hoechst The high temperature (T) behavior of Li$_{0.9}$Mo$_6$O$_{17}$ is that of a one dimensional (1D) metal so that low T charge density wave (CDW) formation could be expected. Below 26K the resistance shows an upturn, but x-ray diffraction, spectroscopic and most transport studies find no evidence for a CDW or its associated single particle gap. Angle integrated photoemission spectroscopy (PES) down to 30K and scanning tunneling microscopy down to 5K both show a power law density of states at the Fermi energy, evidence that the 1D metal survives until superconductivity sets in at 1.9K. However recent magnetotransport studies [1] motivated the proposal of an electronically stabilized CDW with a small gap (1 meV) undetected in previous work. We address this general issue with high resolution (4meV) PES down to 4K, low T transport, and higher T angle resolved PES.\\[4pt] [1] Xu et al, PRL 102, 206602 (2009) [Preview Abstract] |
Tuesday, March 16, 2010 4:30PM - 4:42PM |
L38.00011: Nonequilibrium exact solution for a charge density wave ordered system driven by a large electric field at zero temperature Wen Shen, James Freericks We generalize the Bloch oscillation problem to the case where a system is in an ordered charge density wave (CDW) phase as described by the Falicov-Kimball model. This problem can be solved exactly at zero temperature and involves evaluating a 2x2 matrix-valued time-ordered product. We examine both the density of states and the current and how they evolve with time after the field is turned on. We do not see any clear evidence for a melting of the CDW due to the presence of a large field, but we do see interesting behavior in the density of states at the Bloch frequencies for different values of the field and interaction strength. [Preview Abstract] |
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