Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Q47: Magnetic Oxides, V2O3 and Related: Experiment |
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Sponsoring Units: DCMP Chair: Dimitri Basov, University of California, San Diego Room: Mile High Ballroom 4F |
Wednesday, March 5, 2014 2:30PM - 2:42PM |
Q47.00001: Dynamics of the insulator to metal transition in high quality V2O3 thin films Elsa Abreu, Siming Wang, Jingdi Zhang, Kun Geng, Xiaoguang Zhao, Kebin Fan, Mengkun Liu, Gabriel Ramirez, Xin Zhang, Ivan K. Schuller, Richard D. Averitt Metal-insulator transitions (MITs) are a striking manifestation of the interactions between the various degrees of freedom in complex materials. Vanadium sesquioxide (V2O3) is a prototypical MIT material, transitioning from an antiferromagnetic insulator to a paramagnetic metal at Tc=170K. We present a detailed investigation of the insulator-to-metal dynamics in single crystalline thin films of V2O3 following optical and far-infrared excitation, measured using THz time domain spectroscopy. Conductivity dynamics induced below Tc by ultrafast photoexcitation can be quantitatively described by nucleation and growth of the metallic volume fraction, which eventually gives rise to the full metallic state of V2O3 on a timescale of about 50ps. We will discuss our results in the broader context of phase transition dynamics of the vanadates and related strongly correlated electron materials. [Preview Abstract] |
Wednesday, March 5, 2014 2:42PM - 2:54PM |
Q47.00002: Probing the structural evolution across the metal-to-insulator transition in thin film VO2 using nonlinear optics Hao Chu, Darius Torchinsky, Siming Wang, Juan Gabriel Ramirez, Ivan K. Schuller, David Hsieh Time-resolved pump-probe studies on VO2 have demonstrated that a phase transition in both the electronic and structural degrees of freedom can be induced using sub-picosecond light pulses. However, typically the electronic and structural degrees of freedom are separately measured using time-resolved optical and diffraction based techniques respectively. Therefore the timescales of electronic and structural dynamics are typically compared across different samples and different experimental setups. Here we introduce the use of rotational anisotropy nonlinear optical generation spectroscopy as a method to probe the structural symmetry of VO2 purely optically. We demonstrate that the low temperature monoclinic and high temperature rutile phases in a VO2 thin film grown on r-cut sapphire (1-102) are clearly resolved using our technique and compared favorably with calculations. We will discuss how a simultaneous probe of ultrafast electronic and structural dynamics in VO2 can be realized using this technique. [Preview Abstract] |
Wednesday, March 5, 2014 2:54PM - 3:06PM |
Q47.00003: Nanoscale Structural Evolution of Electrically Driven Insulator to Metal Transition in Vanadium Dioxide Greg Stone, Eugene Freeman, Nikhil Shukla, Hanjong Paik, Jarrett Moyer, Zhonghou Cai, Haidan Wen, Roman Engel-Herbert, Darrell Schlom, Venkatraman Gopalan, Suman Datta We report the evolution of local structural of tensile strained vanadium dioxide thin films during an electrically driven insulator to metal transition by nanoscale hard X-ray diffraction. Evaluation of the Bragg diffraction intensity reveals a narrow metallic filament with rutile structure to be the dominant conduction pathway for the electrically driven insulator to metal transition, while the remainder of the channel area remained the monoclinic M1 phase. The filament dimensions were estimated using simultaneous electrical probing and nanoscale X-ray diffraction measurements. Analysis revealed that the width of the conducting channel can be tuned externally using resistive loads in series allowing for the manipulation of the M1/R phase ratio in the phase coexistence regime. [Preview Abstract] |
Wednesday, March 5, 2014 3:06PM - 3:18PM |
Q47.00004: Temperature-driven and photo-induced MIT behaviors of VO$_{2}$ nanowires Ahrum Sohn, Dong-Wook Kim, Ji-Won Byun, Jeong Min Baik VO$_{2}$ shows a metal-insulator transition (MIT) and structural phase transition (SPT) at critical temperature (Tc) of 343K. It has been known that the MIT and SPT behaviors of VO$_{2}$ can be tuned by external stimuli such as light, electric-field, and strain. We carried out comparative studies of MIT behaviors of VO$_{2}$ nanowires during heating-cooling cycles with and without illumination using several light sources (red, blue, and UV). Light can induce change in Tc and hysteresis width of the resistance change. We have investigated influences of light on SPT during MIT. In this presentation, we will discuss possible physical origins for the photo-induced effects on the MIT behaviors of the VO$_{2}$ nanowires. [Preview Abstract] |
Wednesday, March 5, 2014 3:18PM - 3:30PM |
Q47.00005: Three Dimensional Infrared Nano-Imaging of Stripe Order in Vanadium Dioxide Mengkun Liu, Martin Wagner, Jingdi Zhang, Alexander McLeod, Salinporn Kittiwatanakul, Zhe Fei, Elsa Abreu, Michael Goldflam, Aaron Sternbach, Siyuan Dai, Kevin West, Jiwei Lu, Stuart Wolf, Richard Averitt, D.N. Basov We report the three dimensional landscape of the stripe state in vanadium dioxide (VO$_{2})$ films. This is achieved via direct visualization with scattering-type scanning near-field optical microscope (s-SNOM) [Phys. Rev. Lett. 111 (9), 096602 (2013)]. The VO$_{2}$ films we investigate in this study are epitaxially grown on [100]$_{\mathrm{R}}$ TiO$_{2}$ substrates and exhibit uniaxial strain induced cracking uniformly along the rutile c axis. With s-SNOM, we show that (1) monoclinic-tetragonal crystal symmetry, (2) in-plane rotational symmetry and (3) out-of-plane (z-axis) symmetry have been spontaneously broken in the vicinity of the phase transition. Our results demonstrate s-SNOM as a powerful approach for bringing new insight into mesoscopic physics in strained metal oxide thin films. [Preview Abstract] |
Wednesday, March 5, 2014 3:30PM - 3:42PM |
Q47.00006: Mott transition and Schottky barrier observation by photocurrent measurement in VO$_{2}$ devices Giwan Seo, Minjung Kim, Bong-Jun Kim, Yong Wook Lee, Ahrum Sohn, Dong-Wook Kim, Hyeonsik Cheong, Hyun-Tak Kim As one of the metal-insulator transition (MIT) mechanism, the Mott transition occurs due to Coulomb interactions of electrons in VO$_{2}$. This suggests that VO$_{2}$ does not undergo the structural phase transition (SPT) when MIT occurs. For observing the Mott transition and Schottky barrier in VO$_{2}$ devices, we simultaneously observe the temperature dependence of photocurrent and local structural observation in the two-terminal VO$_{2}$ devices by using scanning photocurrent microscopy, which is a typical method for showing images of nanometer-length scale and Raman spectroscopy, respectively. In particular, the photocurrent between two electrodes through VO$_{2}$ channel increases due to the variation of schottky barrier height. Furthermore, the work functions of VO$_{2}$ thin film is investigated while varying the device temperature, which could assure the Schottky contact formation. We also find the metallic phase with monoclinic structure below a conventional transition temperature of VO$_{2}$ ($\sim$ 68 $^{\circ}$C), indicating the Mott transition of VO$_{2}$. [Preview Abstract] |
Wednesday, March 5, 2014 3:42PM - 3:54PM |
Q47.00007: Evidence of the metal-insulator transition in ultrathin V2O3 films Mariela Menghini, Leander Dillemans, Ruben Lieten, Tomas Smets, Chen-Yi Su, Jean Pierre Locquet We report on the strain state and transport properties of V2O3 single layers and V2O3/Cr2O3 bilayers deposited by Molecular Beam Epitaxy on (0001)-Al2O3 substrates. We find that the metal-insulator transition is strongly attenuated in V2O3 layers of 6 and 4 nm grown coherently on Al2O3. This is in contrast with V2O3 layers grown on Cr2O3 buffer layers which exhibit a metal-insulator transition. Our results provide evidence for the existence of a metal-insulator transition in ultra-thin films. These findings are relevant for the understanding of V2O3 properties in the proximity of interfaces and integration of correlated electron systems in devices. [Preview Abstract] |
Wednesday, March 5, 2014 3:54PM - 4:06PM |
Q47.00008: In situ diffraction studies of H$_{x}$VO$_{2}$ and D$_{x}$VO$_{2}$ D. Natelson, N. Tumanov, V. Ban, Y. Filinchuk, H. Ji, J. Wei, M.W. Swift, A.H. Nevidomskyy Vanadium dioxide exhibits a first-order phase transition at around 338 K between a high temperature, tetragonal, metallic state (T) and a low temperature, monoclinic, insulating state (M1), driven by electron-electron and electron-lattice interactions. Intercalation of VO2 with atomic hydrogen has been demonstrated, with evidence that this doping suppresses the transition. However, the effects of intercalated H on the crystal structure of the resulting hydride had not been examined in detail. Here we report synchrotron and neutron diffraction studies of this material system, mapping out the structural phase diagram as a function of temperature and hydrogen content. In addition to the original T and M1 phases, we find two orthorhombic phases, O1 and O2, which are stabilized at higher hydrogen content. We present density functional calculations that confirm the metallicity of these states. The intercalation of hydrogen above a critical fraction suppresses the metal-insulator transition entirely. [Preview Abstract] |
Wednesday, March 5, 2014 4:06PM - 4:18PM |
Q47.00009: The M2 phase of vanadium dioxide: a view from infrared and optical spectroscopy T.J. Huffman, Peng Xu, M.M. Qazilbash, Joonseok Yoon, Honglyoul Ju, R. Smith, G.L. Carr Bulk single crystalline vanadium dioxide (VO$_{2}$) undergoes a metal-insulator transition (MIT) at 340K. This thermally-driven MIT is accompanied by a structural phase transition that results in pairing of all vanadium ions in the insulating, monoclinic M$_{1}$ phase. However, there also exists an insulating monoclinic M$_{2}$ phase, usually only accessible via external strain or chemical doping, in which only half of the vanadium chains exhibit pairing. The M$_{2}$ phase of VO$_{2}$ is vital for understanding the roles of electronic correlations and vanadium pairing to the MIT. Recent x-ray diffraction studies show that small pure VO$_{2}$ crystals can exhibit an M$_{2}$ phase below 318K, likely due to internal strain.\footnote{ B.S. Mun et al. Physica Status Solidi (RRL) - Rapid Research Letters 5, 107 (2011).} These crystals undergo phase transitions from M$_{2}$ to M$_{1}$ and from M$_{1}$ to rutile metal upon heating. We have performed reflectance micro-spectroscopy with polarized light and generalized spectroscopic micro-ellipsometry between 12 meV and 5.5 eV on these VO$_{2}$ crystals as a function of temperature, uncomplicated by external strain or chemical doping. We report infrared and optical data on the M$_{1}$, M$_{2}$ and rutile phases and compare electronic and phonon properties of M$_{1}$ and M$_{2}$ phases. [Preview Abstract] |
Wednesday, March 5, 2014 4:18PM - 4:30PM |
Q47.00010: X-ray and neutron scattering studies of microstructure and dynamics in VO$_{2}$ John Budai, Jiawang Hong, Michael Manley, Olivier Delaire, Eliot Specht, Chen Li, Jon Tischler, Ayman Said, Douglas Abernathy, Bogdan Leu, Alexander Tselev, Lynn Boatner, Robert McQueeney Vanadium dioxide is a strongly correlated material that exhibits a well-studied, but poorly understood, metal-insulator transition coupled with a tetragonal-monoclinic structural phase transition near 340 K. We have combined synchrotron x-ray and spallation neutron scattering measurements to investigate microstructure and lattice dynamics in VO$_{2}$. Submicron-resolution x-ray microdiffraction studies reveal local phase coexistence driven by strain effects within individual single-microcrystals. Macroscopic diffuse scattering and inelastic x-ray and neutron scattering measurements reveal unusual features in the rutile phonon dispersions at particular locations in reciprocal space, including temperature-dependent dispersions near the R-point. Comparisons of measurements with ab initio molecular dynamics calculations indicate that anharmonicity plays a central role in determining the lattice vibrations and hence physical properties in this system. [Preview Abstract] |
Wednesday, March 5, 2014 4:30PM - 4:42PM |
Q47.00011: Inelastic Neutron Scattering studies of pure and Mo doped VO$_{2}$ Arnab Banerjee, Garrett E. Granroth, Yuen Yiu, Adam A. Aczel, Alexander I. Koleshnikov, Huxia Luo, Robert J. Cava, Stephen E. Nagler For the last half-century~VO$_{2}$ has been viewed as an~archetypal system for studying~the~metal-insulator~transition (MIT). Moreover, there is currently intense interest in this material arising from its promising use in fast energy efficient electronic devices.~ There are key unresolved issues connected with the origin of ~the MIT, including the role of magnetism arising from the S$=$1/2 V$^{4+}$ ions.~ It is known that below 340 K in undoped VO$_{2}$ the V ions form structural dimers in the insulating M1 monoclinic phase.~ Here we report the results of new inelastic neutron scattering measurements of VO$_{2}$ and V$_{0.75}$Mo$_{0.25}$O$_{2}$. Using the~SEQUOIA chopper spectrometer at the SNS~possible lattice and magnetic excitations for energies up to 600 meV were investigated. We discuss the results in the context of current ideas concerning the MIT in VO$_{2}$. [Preview Abstract] |
Wednesday, March 5, 2014 4:42PM - 4:54PM |
Q47.00012: Atomic hydrogen doping in single-crystal vanadium dioxide Heng Ji, Will Hardy, Jiang Wei, Jian Lin, Hanjong Paik, Darrell Schlom, Douglas Natelson Vanadium dioxide is a strongly correlated material with a bulk metal-to-insulator transition (MIT) near 340 K. Previous experiments in single-crystal nanowires (J. Wei et al., Nature Nano. 7, 357-362 (2012)) have shown that catalytic doping with atomic hydrogen can stabilize the high temperature metallic state. In this experiment, we used a hot filament source to split hydrogen molecules and directly dope atomic hydrogen into VO2 material, including epitaxial films and nanowires, without any catalyst. From observations of the wire samples, we infer the relative diffusion rates of H in the monoclinic and rutile crystal structures. Transport measurements of the doped film samples show no temperature-driven transition, but rather a conducting state down to 2K. We present Hall and magnetoresistance measurements on macroscale and mesoscale devices fabricated from the doped films. [Preview Abstract] |
Wednesday, March 5, 2014 4:54PM - 5:06PM |
Q47.00013: Effect of thickness on the film strain and metal-semiconductor transition of VO$_{2}$ thin films Salinporn Kittiwatanakul, Stuart Wolf, Jiwei Lu Many applications of VO$_{2}$ will benefit from the extensive tunability of the Metal to Semiconductor Transition (MST) of VO$_{2}$, which is very sensitive to the film strain and the oxygen stoichiometry [1,2]. Reactive Bias Target Ion Beam Deposition was used to deposit epitaxial VO$_{2}$ thin films on (100), (011), and (001) TiO$_{2}$ substrates, and highly textured VO$_{2}$ on $c$-Al$_{2}$O$_{3}$ with thicknesses in the range of 5-17 nm. X-ray diffractometry confirmed the single-phase nature of the VO$_{2}$ films, and was also used to determine the lattice parameters. Due to the substrate clamping effect, there are very large strains introduced (up to 3.4{\%}), that affect the transition temperatures (T$_{\mathrm{MST}})$. For the 5nm VO$_{2}$/(100) TiO$_{2}$, T$_{\mathrm{MST}}$ is raised above 430 K, which is much higher than in previous reports. The resistivity of this sample changed about 4 orders of magnitude during the transition from a semiconductor to a metal. \\[4pt] [1] S Kittiwatanakul, et al., Journal of Applied Physics 114 (5), 053703-053703-5 (2013) \\[0pt] [2] K. G. West, et al. Journal of Vacuum Science {\&} Technology A 26(1): 133-139 (2008) [Preview Abstract] |
Wednesday, March 5, 2014 5:06PM - 5:18PM |
Q47.00014: Strain-induced anisotropy in VO$_{2}$ film for metamaterial resonance switching and frequency tuning Daan Leiva, Terry Dunlop, Raul Torrico, Robert Marvel, Jed Ziegler, Richard Haglund, Yohannes Abate Vanadium dioxide (VO$_{2})$ undergoes fascinating first order insulator-to-metal phase transition (IMT) around 68 $^{\circ}$C. We demonstrate VO$_{2}$ that thin-films grown on Si substrate exhibit strain induced metallic streaks that are unidirectional during IMT. We unveil the nanoscale formation and spatial dynamics of these streaks and further use the unique anisotropic property of the VO$_{2}$ film to dynamically tune the metamaterial resonances. We reveal thermal control of the metamaterial infrared resonances by nanoscale spatial near-field imaging of both the metallic streaks phase evolution on VO$_{2}$ film and the resonance states of the metamaterial. [Preview Abstract] |
Wednesday, March 5, 2014 5:18PM - 5:30PM |
Q47.00015: Disorder-dominated Ultrafast Dynamics in Vanadium Dioxide Nathaniel Brady, Kannatassen Appavoo, Rohit Prasankumar, Richard Haglund, David Hilton We have performed nondegenerate ultrafast pump-probe spectroscopy of the insulator-to-metal phase transition in vanadium dioxide ($\mathrm{VO_2}$) on several different samples of varying disorder as functions of temperature and pump fluence. Our results are inconsistent with the commonly used assumption of homogeneous nucleation and growth of metallic islands in the parent semiconducting phase and indicate the strong role of disorder on the ultrafast dynamical response. [Preview Abstract] |
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