Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session B12: Organic Conductors and Strongly Correlated 2D Systems |
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Sponsoring Units: DCMP Chair: Victor Yakovenko, University of Maryland Room: Morial Convention Center 203 |
Monday, March 10, 2008 11:15AM - 11:27AM |
B12.00001: The metal insulator transition in correlated quasi-one-dimensional organic conductors Claude Bourbonnais, Abdelouahab Sedeki We use a two-loop functional renormalization group approach to calculate the quasi- particle weight along the Fermi surface in the framework of the quasi-one- dimensional electron gas model which includes weak Umklapp scattering at half- filling. The location and evolution of cold and hot spots for electron-electron scattering is described and the Fermi surface reconstruction is clarified as a function of the amplitude of Umklapp scattering. The results are applied to the Mott transition in the Fabre salts series (TMTTF)$_2$X where the emergence of a Fermi surface is found as a consequence of electronic deconfinement under the application of hydrostatic pressure. [Preview Abstract] |
Monday, March 10, 2008 11:27AM - 11:39AM |
B12.00002: Numerical Study of Finite-Temperature Phase Transitions in Quasi-One-Dimensional Molecular Conductors Yuichi Otsuka, Hitoshi Seo, Yukitoshi Motome, Takeo Kato We have theoretically investigated the charge ordering, the dimer Mott, and the spin-Peierls phase transitions in quarter-filled quasi-one-dimensional organic conductors, such as DCNQI$_{2}X$ and TMTTF$_{2}X$, by considering the extended Hubbard model with electron-lattice couplings and inter-chain Coulomb interaction. We apply the stochastic-series-expansion quantum Monte Carlo method to the effective one-dimensional model obtained by the adiabatic and inter-chain mean-field approximation. Temperature dependences of the order parameters and the susceptibilities are calculated for the charge ordering, the dimer Mott, and the spin-Peierls transitions. The results show a competition between the charge-ordered and dimer Mott insulating states, consistent with our previous work [1], and both of them undergo the spin-Peierls transition at low temperatures. There, two types of spin-Peierls phases with spin gap appear in competition with showing different orderings of period four in lattice distortion and charge disproportionation. [1] H. Seo, Y. Motome, and T. Kato, J. Phys. Soc. Jpn. {\bf 76}, 013707 (2007). [Preview Abstract] |
Monday, March 10, 2008 11:39AM - 11:51AM |
B12.00003: High field ESR on tau phase conductor --from GHz to THz-. Takahisa Tokumoto, J. van Tol, L.-C. Brunel, D. Graf, J.S. Brooks, Y. Oshima, G. Papavassiliou Organic conductors have exotic electronic and magnetic properties ranging from the possibility of unconventional, anisotropic superconductivity, to the observation of a variety of ground states such as charge-density waves, spin-density waves, field-induced spin density waves, and the observation of quantum Hall effect, or a spin-Peierls state. One example is tau - [P-(S, S) -- DMEDT-TTF]2(AuBr2)1+y ($\sim $0.75). The crystal structure of this quasi two dimensional organic compound is tetragonal with unit cell dimensions: a = 7.3546 A and c = 67.977 A. Even though there are no magnetic ions in the system, several measurements indicate magnetic ordering at low temperature and under magnetic fields. Furthermore, this compound exhibits field induced hysteretic MI transition above 38T with an inkling of weak ferromagnetism. We investigate the origin of the magnetic behavior by conducting a CW ESR study from 90GHz to 1.2 THz. Results and analysis will be presented. [Preview Abstract] |
Monday, March 10, 2008 11:51AM - 12:03PM |
B12.00004: First principles study of the charge transfer salt $\kappa$-(BEDT-TTF)$_2$Cu(CN)$_3$ Harald O. Jeschke, Hem C. Kandpal, Roser Valenti The charge transfer salt $\kappa$-(BEDT-TTF)$_2$Cu(CN)$_3$ has attracted a lot of attention due to experimental evidence that it is a realization of a spin liquid: no magnetic ordering was found down to 32 mK. For a good description of this behavior, it is crucial to consider the appropriate effective model for this system. Here, we present electronic structure calculations in the frame of density functional theory (DFT) and derive an effective model with the NMTO (N-th order muffin tin orbital) downfolding method and discuss its features. Since from X-ray diffraction, the structure of $\kappa$-(BEDT-TTF)$_2$Cu(CN)$_3$ has been determined without hydrogen positions, we first prepare a very similar structure including hydrogen atoms and carefully relax it using the projector augmented wave method. This structure is then used for the DFT and NMTO analysis. [Preview Abstract] |
Monday, March 10, 2008 12:03PM - 12:15PM |
B12.00005: Charge frustration and novel electron-lattice coupled phase transition in organic conductor DI-DCNQI$_2$Ag Hitoshi Seo, Yukitoshi Motome We have theoretically investigated the phase transition accompanying charge ordering in 1/4-filled quasi-one-dimensional organic conductor DI-DCNQI$_2$Ag. The nature of this phase transition at 220 K has been under debate since the first direct observation of charge ordering among organic conductors by Hiraki and Kanoda[1]. In this study, motivated by a recent synchrotron radiation x-ray study by Kakiuchi {\it et al.}[2], we investigate a three-dimensional interacting spinless fermion model coupled to the lattice degree of freedom. We have found that the peculiar ``spiral frustration'' existing in the interchain Coulomb interaction destabilizes simple Wigner crystal-type charge order and gives rise to a novel state where different chains show different orders and align periodically: charge order, lattice dimerization, and a co-existence of them. The co-existence of these two orders was in fact predicted in our previous study for the non-frustrated case[3], which was stabilized as a result of competing interactions. In contrast, the co-existence in the present study is obtained by compromising the frustration in charge sector. [1] K. Hiraki and K. Kanoda, Phys. Rev. Lett. {\bf 80} (1998) 4737. [2] T. Kakiuchi {\it et al.}, Phys. Rev. Lett. {\bf 98} (2007) 066402. [3] H. Seo, Y. Motome, and T. Kato, J. Phys. Soc. Jpn. {\bf 76} (2007) 013707. [Preview Abstract] |
Monday, March 10, 2008 12:15PM - 12:27PM |
B12.00006: Finite size effects in micro- and nanocrystals of (TMTSF)$_{2}$ClO$_{4}$ P. Dhakal, J.I. Oh, M.J. Naughton We report transport measurements in micro- and nanosized crystals of the molecular organic (super)conductor (TMTSF)$_{2}$ClO$_{4}$. Synthesized using the standard electrocrystallization process, various techniques such as focus ion beam-induced metallization, photo lithography, and atomic layer deposition were then employed to successfully make micro- and nano-electrodes contacting these samples. In addition, FIB sculpting was used to reshape crystals to reduce their sizes. We have successfully measured crystals with dimensions as small as 300 nm. We have observed that electrical transport behaviors of these finite sized crystals are very different from those of their parent bulk crystals. We will discuss our observations in terms of various origins such as finite size effects, fabrication-induced defects, and combinations thereof. [Preview Abstract] |
Monday, March 10, 2008 12:27PM - 12:39PM |
B12.00007: Pulsed-field study of the interference commensurate effect in quasi-one-dimensional organic conductors J. Roy, J.I. Oh, H. Yoshino, P. Dhakal, M.J. Naughton We report angle-dependent magnetoresistance oscillations for fields up to 43 T oriented mainly in the most conducting \textbf{\textit{x}}\textbf{-}\textbf{\textit{y}} plane, with small field component along the least conducting \textbf{\textit{z}} axis, in the q1d compounds (TMTSF)$_{2}$ClO$_{4}$ and (DMET)$_{2}$I$_{3}$ at 1.5 K. A hybrid plastic-metal cryoprobe system with pseudo dual-axis rotation has been built for these pulsed-field measurements. Due to the interference commensurate effect, (aka Lee-Naughton oscillations) [1-3], we have observed rich magnetoresistance oscillations, resulting from an interference effect of commensurate electron trajectories in the extended Brillouin zone. Also, we have found that, as theoretically expected [2], field-dependent magnetoresistance shows 1D and 2D transport behavior at local resistance maxima and$^{ }$minima (versus field angle), respectively. \newline [1] I.J. Lee and M.J. Naughton, Phys. Rev. B \textbf{57}, 7423 (1998).\newline [2] A.G. Lebed, \textit{et al}., Phys. Rev. Lett. \textbf{91}, 187003 (2003).\newline [3] H.I. Ha, \textit{et al}., Phys. Rev. B \textbf{73}, 033107 (2006). [Preview Abstract] |
Monday, March 10, 2008 12:39PM - 12:51PM |
B12.00008: Acoustic properties of quasi-one-dimensional organic conductor (TMTSF)$_{2}$ClO$_{4}$ in the relaxed state: Superconductivity and FISDW anomalies. Alexandre Langlois, Mario Poirier, Claude Bourbonnais, Klaus Bechgaard Through competing electronic instabilities, the anion sublattice plays an important role in the rich phase diagram of the Bechgaard salts. In the quasi-one-dimensional organic conductor (TMTSF)$_{2}$ClO$_{4}$, anion ordering at 24 K affects the nesting properties of the Fermi surface and controls the stability of the superconducting phase below 1.2 K at ambient pressure. Moreover, the field induced spin density wave phases FISDW, one of the several features induced by a magnetic field in this compound, are also sensitive to the symmetry of the anions. In order to address the coupling issue between the lattice and these electronic instabilities, we have performed the first ultrasonic measurements on (TMTSF)$_{2}$ClO$_{4}$ in the relaxed state below 4 K using longitudinal and transverses waves (30-500 MHz). If low-frequency vibrating reed experiments have revealed magneto-elastic anomalies in the FISDW phases [1], the superconducting one was never investigated by similar techniques. We report anomalies in the ultrasonic velocity and attenuation for the superconducting and the FISDW phases. The coupling of these phases to the lattice is discussed in relation with the known T-B phase diagram. [1] X.D. Shi \textit{et al}., Phys. Rev. B. 50, 1984 (1994). [Preview Abstract] |
Monday, March 10, 2008 12:51PM - 1:03PM |
B12.00009: Spin dynamics of the field-induced spin density wave phases in (TMTSF)$_2$ClO$_4$ in tilted magnetic fields L.L. Lumata, J.S. Brooks, A.P. Reyes, P.L. Kuhns, S.E. Brown, H.B. Cui, J.-I. Yamada The spin dynamics of the different subphases of the field-induced spin density wave (FISDW) ground state in (TMTSF)$_2$ClO$_4$ was investigated using simultaneous $^{77}$Se nuclear magnetic resonance (NMR) and electrical transport. The metallic and FISDW phases were accessed by rotating the sample along its most conducting axis in a constant magnetic field H and constant temperature. At a fixed field of 30 T and constant temperature 1.47K, we report observation of divergence in the spin-lattice relaxation rate 1/T$_1$ at angles corresponding to H$_{\perp}$=H$\cos(\theta)$ $\sim$ 6.4T, 15.9T, and 26T FISDW phase transitions. There is a gradual increase in 1/T$_1$ in the 2nd-order/FISDW cascade region and a nearly metallic-like behavior deep in the final$\backslash$reentrant SDW phase is observed. RF enhancements in the metallic and FISDW phases were also measured. The details will be discussed. [Preview Abstract] |
Monday, March 10, 2008 1:03PM - 1:15PM |
B12.00010: Interlayer Cooperon correction to angular-dependent magnetoresistance in layered metals Malcolm Kennett, Ross McKenzie Studies of angle-dependent magnetoresistance oscillations (AMRO) in the interlayer conductivity of layered metals have generally considered semi-classical electron transport. We consider a quantum correction to the semi-classical conductivity that arises from what can be described as an interlayer Cooperon. This depends on both the disorder potential within a layer and the correlations of the disorder potential between layers. We compare our results with existing experimental data on organic charge transfer salts that is not explained within the standard semi-classical transport picture. In particular, our results may be relevant for weak localization-like effects that have been seen when the applied magnetic field is close to parallel to the conducting layers. [Preview Abstract] |
Monday, March 10, 2008 1:15PM - 1:27PM |
B12.00011: Coulomb drag at zero temperature Alex Levchenko, Alex Kamenev We show that the Coulomb drag effect exhibits saturation at small temperatures, when calculated to the third order in the interlayer interactions. The zero-temperature transresistance is inversely proportional to the third power of the dimensionless sheet conductance. The effect is therefore the strongest in low mobility samples. This behavior should be contrasted with the conventional (second order) prediction that the transresistance scales as a certain power of temperature and is almost mobility-independent. The result demonstrates that the zero-temperature drag is not an unambiguous signature of a strongly-coupled state in double-layer systems. [Preview Abstract] |
Monday, March 10, 2008 1:27PM - 1:39PM |
B12.00012: Collective modes in quantum electron glasses and electron-assisted hopping Markus Mueller, Lev Ioffe We study electronic transport in Anderson insulators with strong Coulomb interactions in dimensions $d\geq 2$. Close to the metal insulator transition where the single particle localization length is much larger than interparticle-distance, the interactions lead to a strongly correlated quantum glass phase. Even though single particle excitations are localized and the system is insulating, there are collective electronic modes which remain delocalized down to parametrically small energies. These collective excitations serve as a continuous bath which can provide the activation energy for variable range hopping transport. This circumvents the energy conservation problem arising when only discrete particle-hole excitations are present. In contrast to the weak and material-dependent phonon-assisted hopping mechanism, the activation by an electronic bath leads to a nearly universal prefactor $e^2/h$ of the Efros-Shklovskii conductance, as is observed in many recent experiments. [Preview Abstract] |
Monday, March 10, 2008 1:39PM - 1:51PM |
B12.00013: Hall effect on the triangular lattice Gladys Leon, Christophe Berthod, Thierry Giamarchi, Andrew Millis We investigate the Hall effect on the two-dimensional triangular lattice. We calculate the high frequency Hall constant $R_H$ and its temperature dependence for three regimes of the Hubbard interaction $U$. In the non-interacting case $U=0$ we find that $R_H$ behaves at temperature $T=0$ like the classical dc Hall constant, $R_H\sim1/ne$. At high $T$ we find a positive $R_H$ increasing linearly with temperature, with a slope depending on the electron density. For small to moderate values of $U$, we study the effect of interactions on $R_H$ within second-order perturbation theory, and we find these effects to be small. The perturbation theory also shows that the electron self-energy is almost local ($k$-independent), suggesting the use of a local approximation as the Dynamical Mean Field Theory (DMFT) method to treat higher values of $U$. We therefore evaluate $R_H$ at large $U$ using both DMFT and the atomic limit of the self-energy, and we compare the results with those obtained at small $U$. Finally, we discuss the relevance of our calculations for the interpretation of recent Hall measurements in cobaltates. [Preview Abstract] |
Monday, March 10, 2008 1:51PM - 2:03PM |
B12.00014: Quantum Phase Transition in a Cold Atomic Spin-Boson Mixture Peter P. Orth, Ivan Stanic, Karyn Le Hur We theoretically implement a spin array in a tunable bosonic environment using cold bosonic atoms with two (hyperfine) ground states, trapped by different potentials [1]. The first specie lies in a deep optical lattice with tightly confining wells and forms a spin array; spin-up/down corresponds to occupation by one/no atom at each site. The second specie forms a superfluid reservoir. Different species are coupled coherently via laser transitions and collisions. Whereas the laser coupling mimics a transverse field for the spins, the coupling to the reservoir phonons (sound modes) induces a ferromagnetic (Ising) coupling as well as dissipation. This results in a peculiar ferro-paramagnetic quantum phase transition where the effect of dissipation can be studied in a controllable manner. \newline \newline [1] Peter P. Orth, Ivan Stanic, and Karyn Le Hur, arXiv:0711.2309 [cond-mat.other]. [Preview Abstract] |
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