Bulletin of the American Physical Society
2014 Annual Meeting of the Far West Section of the APS
Volume 59, Number 14
Friday–Saturday, October 24–25, 2014; Reno, Nevada
Session C3: Condensed Matter and Material Science |
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Chair: Sergey Savrasov, University of California, Davis Room: JCSU 323 |
Friday, October 24, 2014 2:00PM - 2:12PM |
C3.00001: Suspended Molybdenum Disulfide Field Effect Transistors Fenglin Wang, Petr Stepanov, Mason Gray, Chun Ning Lau We fabricate suspended molybdenum disulfide (MoS$_{\mathrm{2}})$ field effect transistors (FET) devices and develop an effective gas annealing technique that significantly improves device quality and increases conductance by 3-4 orders of magnitude. Mobility of the suspended devices ranges from 0.01 to 10 cm$^{\mathrm{2}}$/Vs before annealing, and 0.5 to 85 cm$^{\mathrm{2}}$/Vs after annealing. Temperature dependence measurements reveal two transport mechanisms: electron-phonon scattering at high temperatures and thermal activation over a gate-tunable barrier height at low temperatures. Our results suggest that transport in these devices is not limited by the substrates, but likely by defects, charge impurities and/or Schottky barriers at the metal-MoS$_{\mathrm{2}}$ interfaces. Finally, this suspended MoS$_{\mathrm{2}}$ device structure provides a versatile platform for other research areas, such as thermal, optical and mechanical studies. [Preview Abstract] |
Friday, October 24, 2014 2:12PM - 2:24PM |
C3.00002: Growth of Au on Ge(110) Alex Dorsett, Bret Stenger, Marshall van Zijll, Catriana Paw U, Shirley Chiang The clean Ge(110) surface is studied using Scanning Tunneling Microscopy (STM) to analyze potential sites for growth. The surface structure and growth mechanism of Au on Ge(110) is characterized with Low Energy Electron Microscopy (LEEM). Au is dosed at room temperature with approximately 0.5 monolayers (ML) of coverage. The temperature is increased up to 800C when the sample is imaged by LEEM As the temperature increases, the Au islands form into much larger one-dimensional structures, with all the islands growing along the same direction. This behavior is similar to that previously observed for Ag on Ge(110),\footnote{Cory H. Mullet, Ph.D. Dissertation, UC Davis, 2012.} although the scale of the islands differs. As the temperature decreases, the island behavior is also studied and reveals rapid island contractions which leave traces on the Ge(110) surface. [Preview Abstract] |
Friday, October 24, 2014 2:24PM - 2:36PM |
C3.00003: Optical Conductivity Studies of Small Polaron Hopping in Sm$_{\mathrm{1-x}}$Sr$_{\mathrm{x}}$TiO$_{3}$ Epitaxial Films William Flaherty, Clayton Jackson, Santosh Raghavan, Adam Hauser, Strange Law, Brandon Isaac, Susanne Stemmer, S. James Allen We present our findings in the optical conductivity in a doping-controlled metal-to-Mott-insulator transition. These samples, grown using hybrid MBE, span the transition from the Mott insulator SmTiO$_{3}$ to metallic, lightly-doped SrTiO$_{3}$. Zhou and Goodenough have studied a wide range of rare earth titanates and found that SmTiO$_{3}$ has thermally activated transport. We plan to measure the optical conductivity of doped samples to determine the conduction mechanism. Using FTIR spectroscopy, we extract the optical conductivity in the 0.06-2.5 eV range. If conduction in Sm$_{\mathrm{1-x}}$Sr$_{\mathrm{x}}$TiO$_{3}$ is due to small polarons, it will have a distinct optical conductivity feature, related to the DC transport, as described by David Emin. Alternatively, conduction could be due to variable-range hopping between defects. Further, from the combination of DC and optical conductivity, we can also test the prediction of Yee and Balents that the metal-to-insulator transition is first-order with percolative phase separation between metallic and localized regions. Such a sample would have a distinct Drude tail plus polaron contributions to its conductivity. [Preview Abstract] |
Friday, October 24, 2014 2:36PM - 2:48PM |
C3.00004: Identifying Topological Order in the Shastry-Sutherland Model via Entanglement Entropy David Ronquillo, Michael Peterson It is known that for a topologically ordered state the area law for the entanglement entropy shows a negative universal additive constant contribution, $-\gamma$, called the topological entanglement entropy. We theoretically study the entanglement entropy of the two-dimensional Shastry-Sutherland quantum antiferromagnet using exact diagonalization on clusters of 16 and 24 spins. By utilizing the Kitaev-Preskill construction [A. Kitaev and J. Preskill, Phys. Rev. Lett. 96, 110404 (2006)] we extract a finite topological term, $-\gamma $, in the region of bond-strength parameter space corresponding to high geometrical frustration. Thus, we provide strong evidence for the existence of an exotic topologically ordered state and shed light on the nature of this model's strongly frustrated, and long controversial, intermediate phase. [Preview Abstract] |
Friday, October 24, 2014 2:48PM - 3:00PM |
C3.00005: Cascading Proximity Effects in Inhomogeneous Superconductor-Feromagnetic Structures Thomas Baker, Adam Richie-Halford, Ovidiu Icreverzi, Andreas Bill When a superconductor is placed near another material, the whole system becomes superconducting by proximity. Paired correlations with a projection on the quantization axis of zero have a shorter coherence length than those with $\pm1$ on the quantization axis. We show that the $\pm1$ projections can generate short range components deep inside a magnetic layer in the middle region of five mutually perpendicular ferromagnets as well as an exchange spring system [1,2]. Measurable consequences including the characteristic signature of short range correlations in the Josephson current of a wide layer and a new type of $0-\pi$ transition will be discussed. \\[4pt] [1] T.E. Baker, A. Richie-Halford, O.E. Icreverzi A. Bill, {\it Euro. Phys. Lett.} {\bf 107}, 17001 (2014)\\[0pt] [2] T.E. Baker, A. Richie-Halford, A. Bill, {\it New J. Phys.} {\bf 16}, 093048 (2014) [Preview Abstract] |
Friday, October 24, 2014 3:00PM - 3:12PM |
C3.00006: Odd-Triplet Superconductivity in SmCo/Py/Nb Thin Films Samuel Hedges, Mikhael Semaan, Jiyeong Gu An s-wave superconductor in close proximity to a nonhomogeneous magnetic field will have the singlet component of the superconducting condensate converted to the odd-triplet component at the superconductor/ferromagnet (S/F) interface. The odd-triplet component can penetrate into the ferromagnet over long distances and is insensitive to the ferromagnet's exchange field. Using an exchange-spring system consisting of SmCo/Py, the noncollinearity of the field can be varied by adjusting the direction and strength of an applied external field. Nb/Py/SmCo thin films were sputtered onto a silicon substrate using DC magnetron sputtering. The resistance and superconducting critical temperature were measured as functions of the applied field strength, direction, temperature, and thickness of the layers. The resistance was found to vary non-monotonically with increasing noncollinearity, which cannot be explained by the proximity effect alone. The behavior could be due to new proximity effects involving exchange spring systems that display complicated magnetic switching behavior. [Preview Abstract] |
Friday, October 24, 2014 3:12PM - 3:24PM |
C3.00007: Photoinduced doping in heterostructures of graphene and boron nitride Salman Kahn, Jairo Velasco Jr, Long Ju, Edwin Hwang, Casey Nosiglia, Hsin Zon Tsai, Wei Yang, Takashi Taniguchi, Kenji Watanabe, Dillon Wong, Juwon Lee, Yuanbo Zhang, Guangyu Zhang, Michael Crommie, Alex Zettl, Feng Wang Van der Waals heterostructures (VDH) provide an exciting new platform for materials engineering, where a variety of layered materials with different electrical, optical and mechanical responses can be stacked together to enable new physics and novel functionalities. To create various VDH, we have employed a ``stamping transfer'' in which two layered materials are exfoliated on separate substrates and then stamped onto each other. Several distinct VDH structures have been realized and characterized through scanned probe and optical measurement schemes. I will discuss recent progress made on these efforts, with an emphasis on optoelectronic measurements of a Graphene/Boron Nitride VDH. [Preview Abstract] |
Friday, October 24, 2014 3:24PM - 3:36PM |
C3.00008: Growing and Characterizing 2D Silica Bilayers on Graphene Epitaxially Grown on Ruthenium(0001)/Sapphire Jeff Guevara, Kenneth Ganezer, Eric Altman Two-dimensional (2D) silica (SiO$_{2})$ glass bilayers are a new form of SiO$_{2}$ that is exactly 2 atoms thick with no dangling bonds. Since 2D silica bilayers have no dangling bonds, it is expected to be a van der Waals material with no detectable covalent bonding. Two-dimensional silica can have many applications in layered graphene electronics and dielectric layers in atomically thin transistors, along with applications as membranes that allow only molecules smaller than a specific size to fit through and where the atomic thickness promises unprecedented throughput. The goal of this research is to determine the optimal conditions for growing a 2D silica bilayer on a uniform graphene monolayer and to also study its characteristics and intrinsic properties when removed from all substrates. The first step is to determine the optimal growth conditions for growing a uniform graphene monolayer on epitaxial ruthenium (0001) on c-plane sapphire. The next step is to determine the optimal growth conditions of 2D silica bilayers on graphene. The 2D silica will then be isolated from the substrate so that its characteristics and intrinsic properties can be studied using Raman spectroscopy, transmission electron microscopy, scanning transmission electron microscopy, and electron energy loss and X-ray emission spectroscopy. [Preview Abstract] |
Friday, October 24, 2014 3:36PM - 3:48PM |
C3.00009: The Log-Lin Metric for Generic Responses in Logarithmic Structures Antony Bourdillon The Log-Lin metric is keystone on the arch that joins experimental quasicrystal data with ideal structure: how does a periodic probe, $e.g. $an X-ray or electron beam, interact with an ``aperiodic'' solid to produce sharp diffraction in geometric space? Based on the known structure [1-2], quasi-structure factors are expanded in geometric series, where the metric serves to overlap the periodic wave onto a logarithmic grid [3]. The metric, now systematically analyzed and simulated, enables measurement from the atomic scale to high order superclusters. The metric is analytically derived from a mathematical constant (pi/tau) that converts the geometric series base tau to the same series base pi. The factor applies to physical clusters of extremely dense, binary, hard-sphere, icosahedral, unit cells.\\[4pt] [1] Bourdillon, A.J., \textit{Micron, }\textbf{51} 21-25, (2013): doi: 10.1016/j.micron.2013.06.004.\\[0pt] [2] Bourdillon, A.J.,\textit{ J. Mod. Phys. }\textbf{5} 488-496 (2014): doi.org/10.4236/jmp.2014.56060.\\[0pt] [3] Bourdillon,A.J.,\textit{ J. Mod. Phys. }\textbf{5} 1079-1084 (2014): doi.org/10.4236/jmp.2014.512109 [Preview Abstract] |
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