Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Z21: Vanadium Oxides II |
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Chair: Mengkun Liu, Stony Brook University Room: 201 |
Friday, March 6, 2015 11:15AM - 11:27AM |
Z21.00001: Study of microstructure effects on the photo-induced Metal-insulator transition in VO$_2$ thin films grown on Al$_2$O$_3$ and TiO$_2$ Elizabeth Radue, Lei Wang, Salinporn Kittiwatanakul, Jiwei Lu, Stuart Wolf, Enrico Rossi, R.A. Lukaszew, Irina Novikova We studied the optical response of the VO$_2$ thin films undergoing photo-induced metal-insulator transition (MIT) of VO$_2$ and found the change in reflectivity over time to be highly dependent on the substrate on which the film was grown [1]. Specifically, we have looked at two different VO$_2$ thin film samples, one grown on TiO$_2$ and one grown on Al$_2$O$_3$, in a pump-probe configuration, and found that the strain and differences in microstructure resulted in substantial difference in the fluence threshold needed to induce MIT, as well in the relaxation times back to the insulating state. By mounting the films in a cryostat, we also found that the fluence needed to achieve full MIT for the film on TiO$_2$ substrate did not depend on the sample temperature, implying that different mechanisms may be playing a stronger role in one film rather than the other for an optically induced transition. \\[4pt] [1] E. Radue et al. arXiv:1410.6438 (2014) [Preview Abstract] |
Friday, March 6, 2015 11:27AM - 11:39AM |
Z21.00002: Surface Plasmon Resonance and Insulator-Metal Transition in Gold and Vanadium Dioxide Bilayer Films Melissa Beebe, Lei Wang, Scott E. Madaras, J. Michael Klopf, Zhaozhu Li, David Brantley, Matthew Heimburger, Russell A. Wincheski, Jiwei Lu, Stuart A. Wolf, R.A. Lukaszew Under certain conditions, thin films of noble metals such as gold and silver exhibit intense surface plasmon polaritons (SPP), in what is called surface plasmon resonance (SPR). These are charge oscillations along the air/film interface resulting from the interactions between an illuminating wave and the free electrons at the conductor's surface. There are many possible applications of the SPR, including new plasmonic optoelectronic devices, biological sensors, and new imaging methods [1,2]. We now present correlated experimental studies and simulations on the modulation of the SPP in Au/VO$_{2}$ bilayers by the metal insulator transition (MIT) of VO$_{2}$, opening up new possible applications. The modification of the SPP wave vector by the thermally-induced MIT in VO$_{2}$ was investigated by measuring the optical reflectivity of the sample when SPP's were excited via gratings patterned on the Au surface and also in Kretchmann configuration in Au/VO$_{2}$ bilayers. \\[4pt] [1] Wang, L.; Yang, K.; Clavero, C.; Nelson, A. J.; Carroll, K. J.; Carpenter, E. E.; Lukaszew, R. A. J. Appl. Phys. 2010, 107 (9), No. 09B303\\[0pt] [2] Huang, X. H.; El-Sayed, I. H.; Qian, W.; El-Sayed, M. A. J. Am. Chem. Soc. 2006, 128 (6), 2115--2120. [Preview Abstract] |
Friday, March 6, 2015 11:39AM - 11:51AM |
Z21.00003: Low-frequency noise spectroscopy of vanadium dioxide along the metal to insulator transition Sahar Keshavarz, Patrick LeClair, Arunava Gupta, Sanjoy Sarker VO$_{\mathrm{2}}$ exhibits ultrafast, reversible metal-insulator transition (MIT) around T $\sim$ 340K. Origin and mechanism of VO$_{\mathrm{2}}$ MIT has been controversial, since it simultaneously undergoes a structural transition. One key feature of the MIT is coexistence of metallic and insulating regions over a broad temperature range. We propose low-frequency noise spectroscopy to clarify the nature of this phase coexistence. Noise spectroscopy is more sensitive to details of current distribution, and thus the distribution of metallic and insulating regions, than traditional transport. Epitaxial films of VO$_{2}$ have been deposited on (100), (110) and (001) TiO$_{\mathrm{2}}$ substrates by CVD and were tested by XRD, resistivity versus temperature, and AFM to ascertain quality. As the result, low-frequency 1/f noise amplitude diverges around onset of transition along c-axis, with noise depending non-monotonically on resistivity. On the other hand, it depends monotonically on resistivity along a-axis. This indicates the critical role of structural dynamics during the transition, and in particular strongly suggests that fluctuations of the V-V dimers along c-axis play a prominent role in MIT. Our findings contradict expectations for noise behavior based on simple percolation models. [Preview Abstract] |
Friday, March 6, 2015 11:51AM - 12:03PM |
Z21.00004: Low temperature electric transport properties of hydrogen-doped VO2 Heng Ji, Will Hardy, Hanjong Paik, Jiang Wei, Darrell Schlom, Douglas Natelson Vanadium dioxide is a strongly correlated material with a bulk metal-to-insulator transition (MIT) near 340 K. Previous experiments have shown that hydrogen can be easily doped into this material, and stabilizes a badly metallic state of the material down to low temperatures. In this work, we present the transport properties of hydrogenated VO2 on the mesoscale at low temperatures via magneto-resistance and Hall measurements of both wire and film samples. We observed positive and negative magneto-resistance depending on crystallographic orientation, implying anisotropy of the electronic structure and scattering. We also observed apparent universal conductance fluctuation despite a high overall resistivity. Low temperature scattering time, carrier densities and other physical parameter have been inferred from the data. [Preview Abstract] |
Friday, March 6, 2015 12:03PM - 12:15PM |
Z21.00005: Hole doping in VO$_{2}$ thin films Salinporn Kittiwatanakul, Ryan Comes, Yuhan Wang, Stuart Wolf, Jiwei Lu Chemical doping has been used to modulate the metal-semiconductor transition in VO$_{2}$ extensively. Here, we investigated the effect of aliovalent Al$^{3+}$ doping in VO$_{2}$ thin films on the Metal-Semiconductor Transition (MST) in comparison with the effect of isovalent Mn$^{4+}$ doping. Raman spectroscopy and x-ray diffractometry were used to confirm the monoclinic phase and estimate the lattice strain caused by the doping. The concentration and the valence state of the dopants observed by XPS will be discussed. The Al$^{3+}$ ions are expected to introduce holes into the conduction band of the VO$_{2}$, and the evidence for hole doping by Al$^{3+}$ was observed by Hall effect measurements. This effect has not been reported previously. Both types of dopants were found to increase the change of the resistivity across the MST, and they also shifted the T$_{\mathrm{MST}}$. [Preview Abstract] |
Friday, March 6, 2015 12:15PM - 12:27PM |
Z21.00006: Visualization of quasiparticle interference on the surface of SrVO$_{3}$ film Yoshinori Okada, Tay-Rong Chang, Ryota Shimizu, Guoqing Chang, Horng-Tay Jeng, Susumu Shiraki, Hsin Lin, Taro Hitosugi Establishing the atomic level mechanism leading to long-lived 2D quasiparticle state (\textit{coherent 2D electronic state}) at surface/interface of perovskite oxide has been an important challenge since such electronic state can host many interesting quantum phenomena. In this study, we probed the electronic structure of SrVO$_{3}$ (001) thin film surface by means of spectroscopic imaging scanning tunneling microscope, which is an ideal approach to probe coherent 2D electronic nature via observation of quasiparticle interference (QPI). For the first time in perovskite oxide, we report the QPI on a SrVO$_{3}$ (001) thin film surface and reveal that the surface of SrVO$_{3}$ is a coherent 2D electronic state. Moreover, we observed that apical oxygen is present on VO$_{2}$-terminated top-most plane. In combination with band calculation, we will discuss the atomic scale mechanism of how coherent 2D electronic state emerges on surface of SrVO$_{3}$, whose bulk electronic state has one electron in degenerated t$_{\mathrm{2g}}$ level. [Preview Abstract] |
Friday, March 6, 2015 12:27PM - 12:39PM |
Z21.00007: Investigation of the effects of the metal-insulator transition of Vanadium sesquioxide onto a proximity coupled ferromagnetic thin film Andrea Fantini, Benjamin Madon, Aakash Pushp, Peng Fa, Jaewoo Jeong, Yari Ferrante, Simone Altendorf, Timothy Phung, Stuart Parkin Vanadium sesquioxide (V2O3) is a classic material exhibiting a metal-insulator transition. It is a paramagnetic metal at room temperature and it becomes an antiferromagnetic insulator when cooled below 160 K, in bulk. We grow atomically smooth thin films of V2O3 (typical thickness 40 nm) by molecular beam epitaxy and cover it with an \textit{in situ} sputtered ultra-thin ferromagnetic (FM) layer (typical thickness 2 nm). We measure the ferromagnetic resonance (FMR) response of the FM layer as a function of temperature across the metal-insulator phase transition of V2O3. We show how the dramatic phase change of V2O3 affects the dynamic magnetic properties of the FM layer. [Preview Abstract] |
Friday, March 6, 2015 12:39PM - 12:51PM |
Z21.00008: TDDFT+DMFT study of the nonequilibrium response in monoclinic VO2 Jose Mario Galicia Hernandez, Volodymyr Turkowski, Talat S. Rahman We study the ultrafast response of insulating (monoclinic) vanadium dioxide system by applying a combination of time-dependent density functional theory (TDDFT) and dynamical mean-field theory (DMFT). Following relaxation of the system using DFT, we calculate its spectrum with DMFT which takes into account inherently electron-electron correlation effects. We consider two types of perturbations: a homogeneous ultrafast laser pulse and a local charge injection. The system response is calculated with TDDFT with the nonadiabatic (frequency-dependent) exchange-correlation (XC) kernel obtained from the DMFT charge susceptibility for the effective Hubbard model of VO2 electronic subsystem. We analyze the details of the dynamics of the breakdown of the metal-insulator transition and the relaxation of the system to equilibrium. In particular, in the case of charge injection we establish the time-dependence of the metallic domain size at different values of the local Coulomb repulsion and exchange energy parameters. We demonstrate that the dynamics of the system is significantly affected by time-resolved electron-electron interactions (memory effects) taken into account through the nonadiabatic XC kernel. [Preview Abstract] |
Friday, March 6, 2015 12:51PM - 1:03PM |
Z21.00009: Direct Hall effect measurement on a single vanadium dioxide nanowire Zheng Yang, Ketaki Sarkar Carrier concentration of the nanowires is one of the most important physical parameters, however, the current approach to estimate the carrier type and concentration in nanowires is an indirect measurement, in which nanowires are fabricated into three-terminal FETs and the carrier type and concentration of the nanowires are determined from FETs characteristics. This indirect measurement leads to inaccuracy comparing to a direct Hall effect measurement. Vanadium dioxide is an attractive material undergo a sharp metal-insulator phase transition showing a 3-5 orders of magnitude resistance change around 340K accompanying with a structural transition from monoclinic to tetragonal phase. [ref: Zheng Yang et al, Annual Review of Materials Research 41, 337 (2011)]. How the free carrier concentration in the vanadium dioxide changes with temperature, especially the temperature regime across phase transition, is an indispensable to be clearly understood towards this motivation. Here, we report our direct measurements of the carrier type, concentration, and mobility of a single oxide nanowire using Hall effect. The vanadium dioxide nanowires were grown using physical vapor transfer method. The nanowire Hall bar devices were fabricated using e-beam lithography and photolithography. [Preview Abstract] |
Friday, March 6, 2015 1:03PM - 1:15PM |
Z21.00010: Crossbar structures of vanadium dioxide nanobeams Zheng Yang, Ketaki Sarkar A crossbar structure composed of two individual one-dimensional nanostructure such as nanowire, nanotube, graphene nanoribbon crossed with each other has been of great interest for nanoelectronic, photonic, and memory device applications as well as novel phenomena in fundamental science. Here we report crossbar nanostructures based on crossed vanadium dioxide nanobeams. Vanadium dioxide show a metal-insulator transition at $\sim$340K with a sharp (3-5 orders of magnitude) resistance change accompanying with a structural change from monoclinic to tetragonal structures. Besides the thermal-triggering, other excitations in forms of electrical, photo, strain can also trigger the phase transition. In recent years lots of efforts have been focused on how to utilize the metal-insulator phase transition in vanadium dioxide for device applications (ref: Zheng Yang et al, Oxide electronics utilizing ultrafast metal-insulator transitions, Annual Review of Materials Research, 2011, 41, 337). In this presentation, the growth, fabrication, structural and electrical properties of the vanadium dioxide nanobeam crossbars will be reported. The potential device applications of vanadium dioxide nanobeam crossbars will be discussed. [Preview Abstract] |
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