Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session V12: Metal Insulator Transition I: Vanadium Oxides and Others |
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Sponsoring Units: DCMP Chair: M. Brian Maple, University of California, San Diego Room: Morial Convention Center 203 |
Thursday, March 13, 2008 11:15AM - 11:27AM |
V12.00001: Electrical measurements at the metal-insulator phase boundary in VO$_{2}$ nanobeams David Cobden, Jiang Wei, Zenghui Wang, Wei Chen We study the electrical properties of vanadium dioxide nanobeams undergoing the metal-insulator transition (MIT), which occurs at a temperature of 67$^{\circ}$C at ambient pressure. The nature of the MIT in bulk VO$_{2}$, although known to involve electron-electron correlations, has remained elusive since its discovery fifty years ago. In nanobeams clamped at both ends there is a coexistence regime which allows electrical measurements along the phase boundary. Remarkably, the resistivity of the insulating phase turns out to be constant along the phase boundary implying that the transition is driven by electron density, consistent with a Mott-type mechanism. The measurements show that the resistance of a domain wall is negligible, and the resistance of a nanowire gives a direct measure of the length of insulating phase present in the wire, allowing one to study the motion of the domain wall electrically with high precision. [Preview Abstract] |
Thursday, March 13, 2008 11:27AM - 11:39AM |
V12.00002: Metal-insulator coexistence in VO$_{2}$ nanobeams Jiang Wei, Zenghui Wang, Wei Chen, David Cobden We study the first-order metal-insulator transition (MIT) in vanadium dioxide nanobeams. The MIT occurs sharply at a temperature of $T_{c}$ = 67$^{\circ}$C at ambient pressure. However, in nanobeams clamped at both ends, and hence subjected to a constant length condition, there is a wide coexistence regime between the two phases, which can be visualized in an optical microscope. Above $T_{c}$ the beam is under axial tension and on warming up follows the phase boundary in the tension/temperature plane. Below $T_{c}$ the beam buckles under compressive strain. The metallic phase can be supercooled by up to 50 °C. Usually there is a single metal-insulator domain wall in each beam, but a mobile bubble-like insulating domain can be induced by applying a nonuniform temperature profile.. [Preview Abstract] |
Thursday, March 13, 2008 11:39AM - 11:51AM |
V12.00003: Correlation between metal-insulator transition characteristics and electronic structure changes in vanadium oxide thin films D. Ruzmetov, V. Narayanamurti, S. Ramanathan, S.D. Senanayake We correlate electron transport data with energy band structure measurements in vanadium oxide thin films with varying V-O stoichiometry across the VO$_{2}$ metal-insulator transition (MIT). A set of vanadium oxide thin films were prepared by reactive DC sputtering from a V target at various oxygen partial pressures resulting in films with different MIT strength as determined from the electrical resistance measurements. The results of the near edge X-ray absorption fine structure spectroscopy (NEXAFS) of the O K-edge in identical VO films are presented. Redistribution of the spectral weight from $\sigma $* to $\pi $* bands is found in the vanadium oxide films exhibiting stronger VO$_{2}$ MIT. This is taken as evidence of the strengthening of the metal-metal ion interaction with respect to the metal-ligand and indirect V-O-V interaction in vanadium oxide films featuring sharp MIT. We observe also a clear correlation between MIT and the width and the area of the lower $\pi $* band which is likely to be due to the emergence of the d$_{\vert \vert}$ band overlapping with $\pi $*. The strengthening of this d$_{\vert \vert}$ band near the Fermi level only in the vanadium oxide compounds displaying the MIT points out the importance of the role of the d$_{\vert \vert}$ band and electron correlations in the phase transition. [Preview Abstract] |
Thursday, March 13, 2008 11:51AM - 12:03PM |
V12.00004: Mott transition in vanadium dioxide (VO$_2$) observed by infrared spectroscopy and nano-imaging M.M. Qazilbash, G.O. Andreev, D.N. Basov, P.-C. Ho, M.B. Maple, M. Brehm, F. Keilmann, A. V. Balatsky, Byung-Gyu Chae, Bong-Jun Kim, Sun Jin Yun, Hyun-Tak Kim The driving mechanism for the temperature-induced insulator-to- metal transition (IMT) in vanadium dioxide (VO$_2$) has been debated for the past five decades. Central to this debate is the relative importance of electron-electron correlations and charge-ordering to the IMT. We report near-field infrared images of VO$_2$ films that directly show the percolative IMT. In combination with far-field infrared spectroscopy, the new data reveal the Mott transition with divergent optical mass in the metallic puddles that emerge at the onset of the IMT. [Preview Abstract] |
Thursday, March 13, 2008 12:03PM - 12:15PM |
V12.00005: Avalanches in the Metal-Insulator transition in Vanadium Oxide nano-scaled junctions Amos Sharoni, Gabriel Ram\'Irez, Ivan K. Schuller We present transport measurements on sub-micron devices of VO$_{2}$. Instead of the usual smooth metal insulator transition, we observe for the first time multiple resistive steps. The temperature driven transition between the two phases occurs through a series of avalanches of different amplitude, ranging over 2 decades of resistance. The data is analyzed assuming a generic normalized probability distribution. Results are similar to those obtained in martensitic transitions or Barkhausen noise in ferromagnets, implying universality of first order phase transition. We will discuss the distribution of resistance avalanches as a function of temperature caused by the percolative nature of resistive transition. In particular we will focus on the effect of the VO$_{2}$ junction dimensions and the transport measurement conditions (such as applied current and temperature ramp rate) on the results. Work supported by the US --Department of Energy. [Preview Abstract] |
Thursday, March 13, 2008 12:15PM - 12:27PM |
V12.00006: Micro X-Ray Diffraction Study of VO$_{2}$ Films -- Separation between Metal-Insulator Transition and Structural Phase Transition Kim Hyun-tak, Kim Boung-jun, Lee Yong wook, Yun Sun Jin, Lim Jung-wook, Shin Tae-ju, Youn Hwa-sick It has been well-known that VO$_{2}$ undergoes both a structural phase transition (SPT) from monoclinic (insulator phase) to tetragonal (metal phase) and a discontinuous first-order metal-insulator transition (MIT) (Jump) near 68$^{o}$C. When the MIT and the SPT occurs simultaneously, the MIT can be regarded as the Peierls transition. When both take place separately, the MIT can be interpreted as the Mott transition. Peierls transiton and Mott transition in VO$_{2}$ remain controversial. We have investigated a relation of the MIT and the SPT which are simultaneously measured by I-V measurement and synchrotron micro X-ray of the 1B2 line in Pohang accelerator Lab., respectively. A used sample is a VO$_{2}$-based two terminal device. The result shows that the MIT and the SPT does not occur simultaneously. (References on the MIT: New J. Phys. 6 (1994) 52 (http://www.njp.org), Appl. Phys. Lett. 86 (2005) 242101, Physica B 369 (2005) 76, Phy. Rev. Lett. 97 (2006) 266401, Appl. Phys. Lett. 90 (2007) 023515). [Preview Abstract] |
Thursday, March 13, 2008 12:27PM - 12:39PM |
V12.00007: Lateral V/VO$_{x}$/V Tunnel Junctions Formed by Anodic Oxidation David Kirkwood, Kevin West, Jiwei Lu, Stuart Wolf Anodization has been found to be a simple and cost effective technique to produce oxide films of many transition metals. In this work, we have used anodic oxidation as a means of fabricating lateral V/VO$_{x}$/V junctions. Vanadium wires grown by ion beam deposition were patterned by lithography and an active working window was defined on the wire. VO$_{x}$ was then grown under galvanostatic control in a two electrode electrochemical micro-cell. A droplet of oxygen rich saturated Boric acid was used as the electrolyte to electrically connect the Vandium working electrode to a Platinum wire counter electrode. A constant current of approximately 100 $\mu $A/cm$^{2}$ was maintained through the cell for various amounts of time. Electrical measurements of the resulting V/VO$_{x}$/V junctions indicate a metal to insulator transition (MIT) near 340 $^{o}$K that is similar to the structural phase transition and accompanied MIT of VO$_{2}$ which occurs at this temperature. A 4-fold change in resistance is observed in the junctions. Below this transition temperature a typical junction behavior is observed with a dramatic change in resistance state from high to low with increasing applied current. This non-linear IV characteristic on the junction with a size of 5 $\mu $m by 15 $\mu $m suggests that the anodized VO$_{x}$ film behaves like a tunneling barrier. [Preview Abstract] |
Thursday, March 13, 2008 12:39PM - 12:51PM |
V12.00008: The metal to insulator transition in correlated materials -- exchange of low and high energy spectral weight Stefan G. Singer, B. Schulz, I. Mahns, M. Bastjan, G. Neuber, A. Goos, P. Saichu, S. Binder, A. Rusydi, K. Horn, S. Eller, M. R\"ubhausen, G. Stryganyuk, L. Cooper, G.A. Sawatzky, O. Sushkov, H. Eisaki, Y. Fujimaki, S. Uchida, K. D\"orr The electronic response of correlated system of manganites and cuprates was investigated by a combination of dc conductivity, ellipsometry, and VUV-reflectance covering an energy range from 0 to 22 eV. By performing a stabilized Kramer-Kronig transformation, we obtain the optical conductivity as a function of temperature around the metal to insulator transition. Our main findings are that changes in the kinetic energy exceed energies of more than 22 eV. Within this range we can establish, that high energy spectral weight gets transferred to low energies into the Drude region. We argue that our findings are general phenomena of correlated materials and outline different scenarios to explain our observations. [Preview Abstract] |
Thursday, March 13, 2008 12:51PM - 1:03PM |
V12.00009: Metal-insulating transition and Zhang-Rice singlets in one-dimensional cuprates: the case of Ca$_{2+x}$Y$_{2-x}$Cu$_5$O$_{10}$ Alessio Filippetti, Vincenzo Fiorentini Chain-like Ca$_{2+x}$Y$_{2-x}$Cu$_5$O$_{10}$ is the ideal prototype of dopable one- dimensional cuprate with zig-zag Cu-O interactions. The observed abundance of Zhang-Rice singlets in the electronic ground state of the system induces peculiar phase transitions in magnetic and conducting properties upon doping. With the use of unconventional first-principles calculations suited for to the study of strong-correlated materials, we describe the change of electronic and magnetic properties as doping is varied from x=0 to full-doped concentration (i.e. one hole each CuO$_2$ unit). Zhang-Rice singlets are key ingredients to understand the behavior of doped CuO2 units and the rise of high-Tc superconductivity in cuprates. We can visualize ZR singlets in space and energy at varying doping concentration, and their influence on magnetic and dielectric properties. ZR singlets are associated to holes localization on the oxygens, appear for holes concentration above 0.25 per CuO$_2$ and persist up to maximum doping (i.e. one hole per CuO$_2$) that is well above the threshold of the metallic regime. Our findings are indicative of the general behavior of low-dimensional doped cuprates and give evidence that first-principles band-energy approaches can be valuably employed to the study of doped cuprates. [Preview Abstract] |
Thursday, March 13, 2008 1:03PM - 1:15PM |
V12.00010: EXAFS and XANES in Fe$_{3-x}$M$_x$O$_4$, M = Zn, Ti, Al with 0 $\leq$ x $<$ 0.065. J. Sabol, D. Owoc, Z. Kakol, C. Kapusta, A. Kozlowski, J. Honig We present an extended EXAFS and XANES study at the Fe K edge of the local structural changes in Fe$_{3-x}$M$_x$O$_4$, M = Zn, Ti, Al, with x within the first and second order Verwey transition regimes. The aim of this work was to investigate how the local Fe symmetry is altered at the transition, in view of the drastic change of the overall crystal structure. The comparison of the interatomic distances and Debye-Waller factors shows that the local Fe-O structure around either the octahedral or tetrahedral Fe atoms in magnetite remains nearly unaltered crossing the Verwey transition. This is also independent of the level of doping and dopant atom, i.e., independent of lattice parameters, as Zn and Ti increase the unit cell volume and Al decreases the unit cell volume. Therefore, the local distortion of Fe sites is not a parameter sensitive enough to elucidate the mechanism of the Verwey transition and the change of its character. An examination of different factors, other than local order, is needed to explain the apparent charge ordering below the Verwey transition temperature \textit{T}$_V$. [Preview Abstract] |
Thursday, March 13, 2008 1:15PM - 1:27PM |
V12.00011: Nonequilibrium Relaxations and Aging Effects near a Metal-Insulator Transition in Two Dimensions Dragana Popovi\'c, Jan Jaroszy\'nski The relaxations of conductivity $\sigma (t)$ have been studied in the glassy regime of a strongly disordered two-dimensional (2D) electron system in Si after a temporary change of carrier density $n_s$ during the waiting time $t_w$. Two types of response have been observed~[1]: (a) monotonic, where relaxations exhibit aging, \textit{i.e.} dependence on history, determined by $t_w$ and temperature; (b) nonmonotonic, where a memory of the sample history is lost. The conditions that separate the two regimes have been determined. A detailed study of the aging regime~[2] reveals an abrupt change in the nature of the glassy phase at the metal-insulator transition (MIT) before it vanishes entirely at a higher density $n_g$. Our results provide further support to theories describing the 2D MIT as the melting of a Coulomb glass, and put constraints on the models of glassy freezing.\\ \noindent [1] J. Jaroszy\'nski and D. Popovi\'c, Phys. Rev. Lett. {\bf 99}, 046405 (2007).\\ \noindent [2] J. Jaroszy\'nski and D. Popovi\'c, Phys. Rev. Lett. {\bf 99}, 216401 (2007). [Preview Abstract] |
Thursday, March 13, 2008 1:27PM - 1:39PM |
V12.00012: Photo-induced Metallic States in a Mott Insulator Takashi Oka In the presence of strong AC electric fields, carriers are continuously produced in an insulator and the system may turn metallic. Such photo-induced insulator-to-metal transition was observed in one-dimensional Mott insulators (Iwai et al. $P.R.L.$ (2003)). We have studied the one-dimensional Hubbard model with strong AC electric fields using the time-dependent density matrix renormalization group method. We have changed the strength of the field as well as the frequency. We have observed that metallic states are produced not only when the photon energy, i.e., the frequency of the AC field, is larger than the gap, but also when it is smaller. However, the field must be stronger than a threshold in the latter case. We have also studied the detailed properties of the photo-induced states by calculating the optical and magnetic correlation function. [Preview Abstract] |
Thursday, March 13, 2008 1:39PM - 1:51PM |
V12.00013: I3+-Ir4+ Charge Disproportionation of Spinel CuIr2S4 investigated by Synchrotron Radiaton Photoemission Han-Jin Noh, E.-J. Cho, H.-D. Kim, J.-Y. Kim, C.-H. Min, B.-G. Park, S.-W. Cheong We have studied the electronic structure of the spinel CuIr$_2 $S$_4$ using synchrotron-radiation photoemission spectroscopy. The phase transition from a high temperature paramagnetic metal to a low temperature diamagnetic insulator at $\sim$230 K is clearly observed through the significant line shape change of the Ir 4$f$ photoemission spectra and the $\sim$0.09 eV gap opening of the valence band spectra. The photon energy dependence of the Ir 4$f$ photoemission spectra enable us to characterize the satellite peaks in the metallic phase of CuIr$_2$S$_4$, providing compelling experimental evidence for the Ir$^{3+}$-Ir$^{4+}$ charge disproportionation in CuIr$_2$S$_4$. [Preview Abstract] |
Thursday, March 13, 2008 1:51PM - 2:03PM |
V12.00014: Local structural aspects of the metal-insulator transition in CuIr$_{2}$S$_{4}$ from total scattering x-ray study E. Bozin, A.S. Masadeh, H.J. Kim, P. Juhas, S.J.L. Billinge, J.F. Mitchell A thiospinel CuIr$\bf _{2}$S$\bf _{4}$ exhibits a metal-insulator (MI) transition at T=230 K, with simultaneous spin-dimerization and charge-ordering [1]. The transition can also be driven by extended exposure to the x-rays at low T [2, 3]. Total x-ray scattering study of CuIr$\bf _{2}$S$\bf _{4}$ was carried out using 100 KeV synchrotron beam and rapid acquisition pair distribution function (RAPDF) approach. The RAPDF results indicate consistency of the local and average structure at high T. At 100 K long x-ray exposure melts the long-range order (LRO) of the dimerization pattern, without affecting the local structure, in agreement with diffuse scattering result [3]. The dependence of the LRO related superlattice peak intensity on the exposure time reveals that the melting occurs within approximately 15 seconds of exposure under experimental conditions used. At 100 K the LRO is recovered without temperature increase quickly after the cessation of the beamtime exposure. Results on Cr doped samples will be addressed as well. [1] P.G. Radaelli {\it et al.}, Nature {\bf 416}, 155 (2002). [2] V. Kiryukhin {\it et al.}, Phys. Rev. Lett. {\bf 97}, 225503 (2006). [3] H. Ishibashi {\it et al.}, Phys. Rev. B {\bf 66}, 144424 (2002). This work is supported by the NSF under grant DMR-0304391. ANL is supported under DOE contract No. DE-AC02-06CH11357. [Preview Abstract] |
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