Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session X41: Strongly Correlated Electrons |
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Sponsoring Units: DMP DCMP Chair: Valery Kiryukhin, Rutgers University Room: 413 |
Thursday, March 19, 2009 2:30PM - 2:42PM |
X41.00001: Breakdown of the BCS Ground State at a Quantum Phase Transition Rafael Jaramillo, Yejun Feng, Thomas Rosenbaum, Jonathan Lang, Zahir Islam, George Srajer, Peter Littlewood We use hydrostatic pressure to suppress the magnetism in elemental chromium, a simple cubic metal that demonstrates a subtle form of itinerant antiferromagnetism, formally equivalent to the BCS state in superconductors. By directly measuring the associated charge order with x-ray diffraction in a diamond anvil cell at low temperatures, we reveal a continuous phase transition driven by fluctuations that destroy the BCS-like state while preserving the strong magnetic interaction between itinerant electrons and holes. Cr is unique among stoichiometric magnetic metals studied to date insofar as the quantum phase transition is continuous in nature, allowing experimental access to the naked quantum singularity and a direct probe of the competition between conventional and exotic order in a theoretically tractable material. [Preview Abstract] |
Thursday, March 19, 2009 2:42PM - 2:54PM |
X41.00002: Ultra-fast domain formation by visible and high-energy light in low-dimensional photoinduced phase transition systems Kaoru Iwano We propose the detection of domain dynamics in a one-dimensional system by using high energy photons such as synchrotron radiation. The domain here means that of a different phase formed in the background of an original phase. Using high energy photons, it is expected that not only $k$=0 states with $k$ being the momentum of its center-of-gravity motion, but also finite $k$ states are possible to to be detected. We theoretically demonstrate how they are observed, with off-resonant inelastic X-ray scatterings and valence photoemissions as concrete examples. In the latter, we particularly show that, in addition to basic two degrees of freedom, namely, the center-of gravity and the spatial size of the domain, spin excitations inside the domain play essential roles. [Preview Abstract] |
Thursday, March 19, 2009 2:54PM - 3:06PM |
X41.00003: Ultrafast photo-induced spin and charge dynamics in correlated electron system Sumio Ishihara, Yu Kanamori, Hiroaki Matsueda Photo-induced phenomena in correlated electron system are one of the attractive themes in recent solid state physics. One of the well known examples is manganites with the perovskite crystal structure. The charge ordered insulating state associated with the antiferromagnetic (AFM) long-range order competes with the ferromagnetic metallic phase. After introduction of the pump photon into the charge-ordered insulating phase, dramatic changes in the optical reflectivity and in the optical Kerr rotation are observed. These results imply that the charge and magnetic structures are changed cooperatively by the photo-irradiation. We present a theoretical study of photo-induced dynamics in a correlated electron system where electronic charge couples with spin and lattice. The generalized double exchange model is analyzed by utilizing the two complementary methods, the exact diagonalization and inhomogeneous Hartree-Fock methods. Time evolutions of the optical absorption spectra, spin correlation, and charge correlation are calculated. There are two time scales in the photo-induced dynamics; the charge and AFM spin orders are collapsed within a short time scale corresponding to 10-100 fs, and the long-range FM spin correlation appears in a long time scale corresponding to a few ps. [Preview Abstract] |
Thursday, March 19, 2009 3:06PM - 3:18PM |
X41.00004: Probing orbitons in YTiO3 with Resonant Inelastic X-ray Scattering Lucas Ament, Giniyat Khaliullin, Jeroen van den Brink In YTiO$_3$, a strongly correlated electron system with degenerate orbitals, orbitons are predicted to exist [1]. The hallmark of collective excitations is dispersion. To observe the orbiton dispersion, the rapidly developing technique of Resonant Inelastic X-ray Scattering (RIXS) is especially well suited. We analyze recent experimental RIXS data on YTiO$_3$ in the Ultrashort Core hole Lifetime framework [2]. The Ti ions in this material have a 3$d^1$ configuration, and the electron occupies one of the three degenerate $t_2g$ orbitals. Many of this compound's ground state properties are explained by assuming that the orbitals on these Ti ions talk to each other through a superexchange mechanism [1]. RIXS could couple to the orbital excitations (orbitons) in these kind of materials in two ways: via modulation of the superexchange interactions [3] and via a shakeup process. We compare our theoretical RIXS spectra to experimental ones, giving strong evidence for the existence of orbitons. // [1] G. Khaliullin and S. Okamoto, Phys. Rev. B 68, 205109 (2003) // [2] J. van den Brink and M. van Veenendaal, Europhys. Lett. 73, 121 (2006); L. J. P. Ament, F. Forte and J. van den Brink, Phys. Rev. B 75, 115118 (2007) // [3] compare F. Forte, L. J. P. Ament and J. van den Brink, PRL (2008) [Preview Abstract] |
Thursday, March 19, 2009 3:18PM - 3:30PM |
X41.00005: Polaronic hole-trapping in doped insulating oxide Cesare Franchini, Georg Kresse, Raimund Podloucky In transition-metal oxides, local electronic correlation effects dominate the physics, and lattice degrees of freedom are often only treated as external perturbations. However, in systems dominated by s and p electrons, electronic correlation is expected to be less important, and in agreement with this conjecture, we show that lattice degrees of freedom are crucial to account for the hole doping driven insulator-to-metal/superconducting transition (IMT) in Ba$_{1-x}$K$_x$BiO$_3$. Specifically, by using hybrid-DFT we show that Bi$^{3+}$ sites trap two holes from the valence band accompanied by a large local lattice distortion, commonly referred to as bipolaronic state. We show that in pure $\rm BaBiO_3$ a single peak in the imaginary part of the dielectric function is visible which corresponds to the charge-ordered excitation between Bi$^{3+}$ and Bi$^{5+}$ sub-bands. Upon hole-doping a second peak emerges at $x=0.125$ connected with the bipolaronic excitation. At $x=0.25$ the bipolaronic peak increases in intensity and is shifted towards lower energy, thus indicating the incipient IMT observed at $x\approx0.3$. Our results describe all relevant experimental results. [Preview Abstract] |
Thursday, March 19, 2009 3:30PM - 3:42PM |
X41.00006: Systematic enhancement in magnetic susceptibilities and a study of Fermi Liquid behaviour of ReT$_{2}$Al$_{10}$ where Re=Y and La, and T =Fe, Ru, and Os Keeseong Park, Yuri Janssen, Moosung Kim, Carlos Marques, Meigan Aronson DC and AC magnetic susceptibilities, specific heat and resistivity are measured for YbFe$_{2}$Al$_{10}$-structure compounds, ReT$_{2}$Al$_{10}$ where Re =Y, and La, and T = Fe, Ru, and Os. The YT$_{2}$Al$_{10}$ show systematically enhancing paramagnetic behavior in magnetic properties from Os to Ru and to Fe, and Fermi-liquid behaviour below around 100 K. With the linear term of the specific heat ($\gamma _{0})$ and the temperature independent susceptibility ($\chi _{0})$ at low temperature, the Stoner enhancement parameter, Z, is utilized to find how close the compounds are to the ferromagnetic ordering, where Z = 1-(3$\mu _{B}^{2}$/$\pi ^{2}$k$_{B}^{2})(\gamma _{0}$/ $\chi _{0})$ . Specifically, YFe$_{2}$Al$_{10}$ shows a larger Z (0.98) than that (0.83) of Pd, a well known example of nearly ferromagnetic materials. The implied proximity to the quantum criticality is tested by a power law analysis , where 1/($\chi -\chi _{0})$=AT$^{\lambda }$ can describe well a wide range (2K to 100K) of AC magnetic susceptibility for YFe$_{2}$Al$_{10}$ with $\lambda $ = 1.19, which is between the mean-field value ($\lambda $ = 1) and that of the three-dimensional Ferromagnetic Heisenberg model ($\lambda $ = 1.33). [Preview Abstract] |
Thursday, March 19, 2009 3:42PM - 3:54PM |
X41.00007: Soliton Wall Superlattice Charge-Density-Wave Phase in Quasi-One-Dimensional Conductor (Per)2Pt(mnt)2 Si Wu, Andrei Lebed We demonstrate that the Pauli's spin splitting effects in a magnetic field improve nesting properties of a realistic quasi-one-dimensional electron spectrum. As a result, a high resistance Peierls charge-density-wave (CDW) phase is stabilized in high enough magnetic fields in (Per)2Pt(mnt)2 conductor. We show that, in low and very high magnetic field, the Pauli spin-splitting effects lead to a stabilization of a soliton wall superlattice (SWS) CDW phase, which is characterized by periodically arranged soliton and anti-soliton walls. We suggest experimental studies of the predicted first order phase transitions between the Peierls and SWS phases to discover a unique SWS phase. It is important that, in the absence of the magnetic field and in the limit of very high magnetic field, the suggested model is equivalent to the exactly solvable model of Brazovskii, Dzyaloshinskii, and Kirova. [Preview Abstract] |
Thursday, March 19, 2009 3:54PM - 4:06PM |
X41.00008: Non Fermi Liquid behavior and disorder in BaVS$_3$ Ana Akrap, Neven Barisic, Florence Rullier-Albenque, Helmuth Berger, Laszlo Forro In strongly correlated BaVS$_3$, the interplay between a wide one-dimensional $d_z^2$ band and the localized $e_g$ electrons leads to a wealth of electronic phases. In this work we investigate the high pressure non-Fermi liquid (NFL) phase of BaVS$_3$ by means of transport measurements, focusing on the influence of disorder, introduced by fast electron irradiation and sulfur deficiency. Our results are interpreted within a novel scenario in which quasi-one dimensional 2$k_F$-CDW fluctuations are responsible for the NFL behavior.\footnote{N. Bari\v{s}i\'c {\it et al.}, arXiv:0712.3393v1} [Preview Abstract] |
Thursday, March 19, 2009 4:06PM - 4:18PM |
X41.00009: The role of charge degrees of freedom in Mott insulators: coupling of dielectric and magnetic properties in Cr-trimer complexes. Ross McDonald, Oscar Ayala Valenzuela, Marcelo Jaime, John Mydosh Materials that are insulating owing to strong electron correlations are pervasive in condensed matter physics-the parent phase of high-Tc cuprates, colossal magnetoresistive manganites and quantum magnets. All are characterized by a large onsite coulomb repulsion relative to the dominant electron hopping. As such, at half-band filling the charge is localized. The properties of these materials are therefore commonly described solely in terms of their spin degrees of freedom, with little attention given to any further role of the charge. Certain classes of Mott insulator are predicted to break this paradigm, providing a direct correlation between the magnetic spin texture and the dielectric properties of a material. We observe such a correlation in Cr- trimer systems, which combined with recent theoretical developments, indicates a purely electronic mechanism for multiferroic behavior. Magnetic field strengths of the order of the exchange interaction strongly perturb the spin texture, which is evident as steps and plateau in the magnetization. The corresponding shifts in dielectric properties reveal the role of the charge degrees of freedom. Electron Spin Resonance (ESR) results and the prospect of novel dipole-active ESR giving rise to the possibility of negative refractive indices will also be discussed. [Preview Abstract] |
Thursday, March 19, 2009 4:18PM - 4:30PM |
X41.00010: The Jahn-Teller effect in doped LiCuO$_2$ Chris Marianetti LiCuO$_2$ displays one of the largest known Jahn-Teller distortions, where Cu$^{3+}$ is in a low spin configuration. Previous density functional theory (DFT) calculations verified the fact that the high spin, non-Jahn-Teller distorted LiCuO$_2$ is a metastable phase. In this work, we use DFT calculations to demonstrate that doping this system with ions that are not Jahn-Teller active allows one to tune the energy difference between the high-spin, non-Jahn-Teller phase and the low-spin, Jahn-Teller phase. This occurs due to the elastic penalty of the non-Jahn-Teller ion in the Jahn-Teller phase. The effect of different non-Jahn-Teller dopants is presented, and the electronic nature of the two respective phases is detailed. [Preview Abstract] |
Thursday, March 19, 2009 4:30PM - 4:42PM |
X41.00011: Scanning tunneling spectroscopy study of electric-pulse-induced electronic inhomogeneities in GaTa$_{4}$Se$_{8}$ Vincent Dubost, Cristian Vaju, Tristan Cren, Benoit Corraze, Francois Debontridder, Etienne Janod, Dimitri Roditchev, Laurent Cario We have recently discovered a bulk Electric Pulse Induced Insulator-Metal Transition and possible superconductivity in the cluster Mott Insulator GaTa$_{4}$Se$_{8 }$[1]. The transport measurements, conducted on single crystals, are consistent with a two-channel model, which suggests that the electric pulse generates electronic inhomogeneities in the bulk of the samples. Our Scanning Tunneling Microscopy/Spectroscopy experiments indeed confirmed that the observed drop in the electric resistance originates from an electronic phase separation with the coexistence of metallic- like and insulating like domains at the nanometer scale [1]. [1] Vaju \textit{et al.} Advanced Materials, \textbf{20} 2760 (2008), Microelectronics engineering \textit{in press}, (2008) [Preview Abstract] |
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