Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session N10: Metal-Insulator Transition II |
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Sponsoring Units: DMP Chair: Erik Helgren, University of California, Berkeley Room: Colorado Convention Center Korbel 1E |
Wednesday, March 7, 2007 8:00AM - 8:12AM |
N10.00001: Infrared study of the metal-insulator transition regime in vanadium dioxide M. M. Qazilbash, B. G. Chae, H. T. Kim, D. N. Basov Vanadium dioxide (VO$_{2})$ undergoes a metal-insulator transition at T$_{c} \quad \approx $ 340 K. The transition region of a VO$_{2}$ film has been studied with infrared ellipsometry and near-normal incidence reflectance between 40 cm$^{-1}$ and 5000 cm$^{-1}$. The measured optical constants are compared to calculations based on effective medium theories. The anomalies in the frequency and temperature dependence of the optical constants will be presented. The implications of the data for the mechanism of the metal-insulator transition will be discussed. [Preview Abstract] |
Wednesday, March 7, 2007 8:12AM - 8:24AM |
N10.00002: Metal-Insulator Transition in Ca$_{1-x}$Na$_{x}$IrO$_{3}$ with Post-Perovskite Structure Kenya Ohgushi, Hirotada Gotou, Takehiko Yagi, Yoko Kiuchi, Fumiko Sakai, Yutaka Ueda We developed a novel solid solution Ca$_{1-x}$Na$_{x}$IrO$_{3}$ (0 $< x \quad <$ 0.37) with the post-perovskite structure [1, 2]. Upon carrier doping into the $S$ = 1/2 antiferromagnetic Mott insulator CaIrO$_{3}$, the magnetic long-range order is gradually destabilized, culminating in a paramagnetic state at $x \quad >$ 0.30, with simultaneous change from the insulating to metallic behavior. The temperature dependence of the resistivity for metallic samples exhibits several characteristic features: (1) the $T^{\alpha }$ dependence with \textit{$\alpha $} $\sim $ 1.2 in the metallic range, (2) the ln$T$ dependence in the weak-localization regime, and (3) the positive magnetoresistance violating the Kohler's rule. These results indicate the anomalous metallic state caused by the strong electron correlation effect is realized on the verge of the Mott transition. [1] Nobuyoshi Miyajima, Kenya Ohgushi, Masaki Ichihara, and Takehiko Yagi, Geophys. Res. Lett. \textbf{33}, L12302 (2006). [2] K. Ohgushi, H. Gotou, T. Yagi, Y. Kiuchi, F. Sakai, and Y. Ueda, submitted. [Preview Abstract] |
Wednesday, March 7, 2007 8:24AM - 8:36AM |
N10.00003: Metal-insulating phase transition in YBa$_2$Cu$_3$O$_{6+x}$ by First-Principles Alessio Filippetti The basic chemistry of YBa$_2$Cu$_3$O$_{6+x}$ represents an hystorical challenge for first-principles approaches, due to the well known difficulty of standard local-spin density functional theories (such as LSDA or GGA) in describing the correct spin-polarized S=1/2 ground-state of Cu (II) ion. Here we employ the pseudo-SIC approach, which is based on an approximate form of self-interaction corrected (SIC) Kohn-Sham Equations and works well in both Mott-insultaing (i.e. x=0) and metallic limit (x=1), to describe the effect of oxygen-doping on the electronic properties of YBa$_2$Cu$_3$O$_{6+x}$. Our results give a sound description of the order-disorder as well as magnetic-non magnetic phase competitions. We show that the phase transition from the antiferromagnetic insulating to the paramagnetic metal is mainly governed by the ordering of doping oxygens in Cu(I)-O-Cu(I) chains, which in turn, subtly affects the chemistry of Cu(II)-O$_2$ planes through a non trivial pattern of p-d couplings. [Preview Abstract] |
Wednesday, March 7, 2007 8:36AM - 8:48AM |
N10.00004: Quantum Monte Carlo Study of an Interaction-Driven Band Insulator to Metal Transition Norman Paris, Karim Bouadim, Frederic Hebert, George Batrouni, Richard Scalettar We study the transitions from band insulator to metal to Mott insulator in the ionic Hubbard model on a two dimensional square lattice using determinant Quantum Monte Carlo. Evaluation of the temperature dependence of the conductivity demonstrates that the metallic region extends for a finite range of interaction values. The Mott phase at strong coupling is accompanied by antiferromagnetic (AF) order. Inclusion of these intersite correlations changes the phase diagram qualitatively compared to dynamical mean field theory. [Preview Abstract] |
Wednesday, March 7, 2007 8:48AM - 9:00AM |
N10.00005: Metal to Nonmagnetic-Insulator Transition in LiVS$_{2}$ Naoyuki Katayama, Minoru Nohara, Masaya Uchida, Hidenori Takagi LiVS$_{2}$ has been reported to exhibit a first order magnetic transition with a drastic decrease in susceptibility at about 310 K$^{[1]}$. In order to clarify the nature of this transition, we performed resistivity, magnetic susceptibility, and electron diffraction measurement for LiVS$_{2}$. The resistivity in LiVS$_{2}$ revealed a metal to insulator (MI) transition at $T_{c} \quad \sim $ 310 K. In the insulating state below $T_{c}$, we observed $\sqrt 3 a_0 \times \sqrt 3 a_0 $superstructure in the electron diffraction, indicating a formation of vanadium trimers in the \textit{ab} plane. Together with the drastic decrease in susceptibility at $T_{c}$, we propose a formation of trimer singlet state below $T_{c}$ for LiVS$_{2}$. Although this ground state is analogous to that observed in the isostructural and isoelectronic oxide LiVO$_{2}^{[2]}$, the MI transition is unique to LiVS$_{2}$. [1] D. W. Murphy \textit{et al.}; Inorg. Chem. \textbf{15} (1976) 17. [2] W. Tian \textit{et al.}; Mater. Res. Bull. \textbf{39} (2004) 1319. [Preview Abstract] |
Wednesday, March 7, 2007 9:00AM - 9:12AM |
N10.00006: Use of Abrikosov-Gorkov Density of State to Extract Spin Polarization at the Metal-Insulator Transition R. V. A. Srivastava, W. Teizer We have discovered and applied an analytical solution of the Abrikosov-Gorkov $^{1}$ density of states (DOS), describing superconductors with impurities, to extract the spin-polarization of 3-dimensional amorphous (a-) Gd$_{x}$Si$_{1-x}$ in the quantum critical regime (QCR) of a magnetic field tunable metal-insulator transition (MIT). The analysis of the experimental spin-polarized (SP) tunneling conductance of an Al/Al$_{2}$O$_{3}$/a-Gd$_{x}$Si$_{1-x}$ planar tunnel junction at T=25mK in parallel magnetic field H$\le $3.0T indicates a larger polarization near the MIT of a-Gd$_{x}$Si$_{1-x}$ (x=0.14) as compared to previous work $^{2}$, where a SP Bardeen-Cooper-Schrieffer DOS $^{3}$ was used. We will present polarization values at different applied magnetic fields in the QCR. \newline $^{1 }$A. A. Abrikosov and L. P. Gor'kov, Zh. Eksperim. I Teor. Fiz. 39, 1781 (1960). A.A. Abrikosov and L.P. Gorkov, Zh. Eksp. Teor. Fiz. 39, 866 (1961). Soviet Phys.---JETP 12, 1243 (1961). \newline $^{2}$ W. Teizer, F. Hellman, and R. C. Dynes. Phys. Rev. B 67, 121102 (2003). \newline $^{3}$ J. Bardeen, L. N. Cooper, and J. R. Schrieffer, Phys. Rev. 108, 1175 (1957). [Preview Abstract] |
Wednesday, March 7, 2007 9:12AM - 9:24AM |
N10.00007: X-ray absorption spectroscopy studies of Vanadium dioxide thin films across the metal-insulator phase transition boundary Dmitry Ruzmetov, Shriram Ramanathan, Sanjaya D. Senanayake X-ray absorption (XAS) and photoemission (XPS) spectroscopy of the V 2p edges and O 1s edge was performed on VO$_{2}$ thin films synthesized by RF sputtering at various conditions. Distinct changes of the electronic structure depending on the film quality, whether the sample is above or below the metal insulator transition (MIT) temperature, and thermal history of the sample are observed. The spacing between 3d$_{\pi }$ and 3d$_{\sigma }$ band peaks probed by O- edge XAS decreases by 0.8eV with concurrent peak broadening for the sample sputtered at lower substrate temperature and consequently having more polycrystalline and disordered character. There is a similar tendency in the V 2p$_{3/2}$ and 2p$_{1/2}$ edges, i.e. the convergence of the doublets for the disordered sample. The temperature dependence of the XAS V and O edges including repeated crossing of the MIT has been studied. The reversible switches of the 3d$_{\pi }$ and 3d$_{\sigma }$ band peak widths in the O-edge on different sides of the MIT are measured while the peak separation remains the same. The abruptness of the band structure transformation at MIT suggests that the band width changes are determined by the VO$_{2}$ MIT phase rather than gradual evolution with temperature. [Preview Abstract] |
Wednesday, March 7, 2007 9:24AM - 9:36AM |
N10.00008: Mott-Hubbard Scenario for the Metal-Insulator Transition in the Two Dimensional Electron Gas Ping Sun We exam the experimental observations of the metal-insulator transition in Si-MOSFET and GaAs quantum well. We find that the observed critical behaviors in the magneto transport experiments can be understood within the Mott-Hubbard scenario. Disorder, while playing an important role in both metallic and insulating phases, does not affect the universal critical behaviors. [Preview Abstract] |
Wednesday, March 7, 2007 9:36AM - 9:48AM |
N10.00009: ABSTRACT WITHDRAWN |
Wednesday, March 7, 2007 9:48AM - 10:00AM |
N10.00010: 2D Wigner crystal: metal to insulator transition via self doping Sergey Pankov, Vladimir Dobrosavljevic We consider a scenario of metal to insulator transition in the 2D Wigner crystal. The Wigner crystal is modeled as a two band (bands represent the site and interstitial orbitals) Hubbard model. It is found that the transition is unstable to the electron self doping, resembling conceptually the liquid-solid transition in Helium III. The self doping is shown to stabilize the metallic phase, pushing the transition to lower electron densities. The implication of the self doping to the compressibility, phase separation and transport properties of the Wigner crystal is discussed. [Preview Abstract] |
Wednesday, March 7, 2007 10:00AM - 10:12AM |
N10.00011: Disappearance of the metal-like behavior in GaAs two-dimensional holes below 30mK. Jian Huang, Jian-Sheng Xia, D. C. Tsui, L.N. Pfeiffer, K.W. West The T-dependence of the resistivity of two-dimensional holes are observed to exhibit two qualitatively different characteristics for a fixed carrier density at temperatures below 100mK. In this putatively metallic regime of the so-called metal-insulator transition, the sign of the derivative of the resistivity with respect to temperature changes from being positive (d$\rho $/dT$>$0) to negative (d$\rho $/dT$<$0) when the temperature is lowered below 30 mK and the resistivity continuously rises with cooling down to 1mK, suggesting a crossover from being metal-like to insulator-like. [Preview Abstract] |
Wednesday, March 7, 2007 10:12AM - 10:24AM |
N10.00012: Metal-insulator transition and domains in suspended VO2 nanobeams Jiang Wei, Wei Chen, Zenghui Wang, David Cobden VO$_{2}$ undergoes a metal-insulator transition (MIT) around 67$^{\circ}$C. We investigate the transition in suspended crystalline nanobeams of VO$_{2}$. The nanobeams are grown by vapor phase deposition on SiO$_{2}$ substrates and contacted by electron beam lithography with chromium-gold metallisation. After suspending them by selectively etching away the substrate, the resulting nanobeams are firmly clamped at the contacts. Under some conditions the MIT occurs suddenly throughout the entire beam, associated with a single hysteretic conductance jump. This is in contrast with the behavior of nanobeams attached to the substrate in which alternating metallic and insulating domains form during the transition. Under other conditions, a single metallic domain forms and grows gradually as temperature is increased. At room temperature the longer beams are buckled, and on warming they unbuckle when the MIT occurs. When a force is applied to bend a suspended nanobeam, alternating domain patterns form in the bent region reflecting the strain field. [Preview Abstract] |
Wednesday, March 7, 2007 10:24AM - 10:36AM |
N10.00013: Physical properties of VO$_{2}$ and V$_{2}$O$_{3}$ nanowires. Wei Chen, Jiang Wei, David Cobden Both VO$_{2}$ and V$_{2}$O$_{3}$ show dramatic metal-insulator transitions, whose manifestations on the nanoscale are not known. We investigate techniques to differentiate and pattern the metallic and insulating domains in small VO$_{2}$ crystals and nanowires grown by vapor phase deposition. For instance, it has been reported that insulating VO$_{2}$ can be metallized by electron beam exposure and by hydrogenation. We attempt to distinguish the domains by scanning probe techniques, including topography and electric force microscopy, and observe a pinning effect of the domains by oscillating strain variations when the nanowire is attached to a substrate. When the strain is released by etching, the pinning is removed. The VO$_{2}$ crystals can be converted to V$_{2}$O$_{3}$ crystals by reducing in hydrogen and annealing. By patterning the V$_{2}$O$_{3}$ on the nanoscale we aim to realize strongly correlated quantum dots. [Preview Abstract] |
Wednesday, March 7, 2007 10:36AM - 10:48AM |
N10.00014: Orientation Studies of Recrystallized Vanadium Dioxide Felipe Rivera, Mike Clemens, Laurel Burk, Robert Davis, Richard Vanfleet Crystalline films and isolated vanadium dioxide particles were obtained through thermal annealing of amorphous vanadium dioxide thin films on silicon dioxide. Vanadium dioxide undergoes an insulator to metal transition near 66 $^{\circ}$C. Orientation Imaging Microscopy (OIM) was used to study the phase and orientation of the crystals formed, as well as to differentiate from different vanadium oxide crystal structures. Kikuchi patterns for the tetragonal phase of vanadium dioxide were used for indexing as the Kikuchi patterns for the two phases are indistinguishable by OIM. There is a preferred orientation for the growth of these crystals with the c axis of the tetragonal phase parallel to the plane of the specimen. Resistance and Capacitance measurements on these films are being performed to study the electronic chracteristics of this phase transition. The results of this study will be presented. [Preview Abstract] |
Wednesday, March 7, 2007 10:48AM - 11:00AM |
N10.00015: Electron Dynamics in Transition Metal Granular Films N.E. Massa, J.C. Denardin, L.M. Socolovsky, M. Knobel, X.X. Zhang Near normal incidence reflectivity spectra of transition metal $\sim $500 nm thick cosputtered granular films on SiO$_{2}$ subtracts were measured from 30 to 11000 cm$^{-1}$ and at temperatures from 30 to 490 K. The reflectivity for Co$_{0.85}$(SO$_{2})_{0.15}$ has a frequency and temperature behavior according to conducting metal oxides. The electron scattering rate denotes an unique relaxation time characteristic of a single type of carriers and has a very strong temperature dependence due to strong electron-phonon interactions. Using small polaron fits we individualize these as related to glass stretching vibrational modes. The optical conductivity of Ni$_{0.61}$(SO$_{2})_{0.39}$, undergoing a metal-insulator transition at $\sim $77 K, has a Drude mode (freer carriers) and a mid-IR band (mid-infrared ``carriers''). This last disorder related strong resonance drives the phase transition by localization decreasing in magnitude as the temperature is lowered and points to a double relaxation process (two different scattering mechanisms). On the other hand, Co$_{0.51}$(SO$_{2})_{0.49}$ has an insulator reflectivity in which a distinctive band at $\sim $1450cm$^{-1}$ originates in electron promotion, localization, and defect induced quasiparticle formation. [Preview Abstract] |
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