Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Q49: Focus Session: Conductivity and Its Control at LaAlO3/SrTiO3 Interfaces |
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Sponsoring Units: DMP Chair: Shahal Ilani, Weizmann Institute of Science Room: Mile High Ballroom 1C |
Wednesday, March 5, 2014 2:30PM - 3:06PM |
Q49.00001: Local conductivity enhancement due to the tetragonal domain structure in LaAlO$_{3}$- SrTiO$_{3}$ heterointerfaces Invited Speaker: Kathryn Moler Progress in the difficult task of growing oxide heterostructures has enabled the field of oxide interface engineering. The ability to control materials properties through interface engineering is demonstrated by the appearance of conductivity at the interface of certain insulators, most famously the \textbraceleft 001\textbraceright interface of the band insulators LaAlO$_{3}$ (LAO) and TiO$_{2}$-terminated SrTiO$_{3}$ (STO). The prevailing explanation of conduction at the interface is electronic reconstruction due to a `polar catastrophe' in which charge migrates from the top LAO layer to the interface. Transport and other measurements in this system display a plethora of diverse physical phenomena. To better understand the interface conductivity, we used scanning superconducting quantum interference device (SQUID) microscopy to image the magnetic field locally generated by current in an interface. At low temperature, we found that the current flowed in conductive narrow paths oriented along the crystallographic axes, embedded in a less conductive background. The configuration of these paths changed upon thermal cycling above the STO cubic to tetragonal structural transition temperature, implying that the local conductivity is strongly modified by the STO tetragonal domain structure. In this talk, I will summarize these results and also report on measurements of conductivity and diamagnetism in related materials that firmly establish the influence of the STO tetragonal domains on electronic properties. [Preview Abstract] |
Wednesday, March 5, 2014 3:06PM - 3:18PM |
Q49.00002: Direct Imaging of Current Flow at the interface of Strained LaAlO3/SrTiO3 Aaron J. Rosenberg, Eric M. Spanton, John R. Kirtley, Christopher Bell, Yanwu Xie, Hiroki Sato, Masayuki Hosoda, Yasuyuki Hikita, Harold Y. Hwang, Kathryn A. Moler At the interface of band insulators LaAlO3 and SrTiO3, recent scanning SQUID and scanning SET studies show that conductivity and charge carrier density are influenced by the tetragonal domain structure of SrTiO3. SQUID imaging shows that transport current flows along more conductive narrow paths within a less conductive background, but the microscopic mechanism of the enhanced conductivity is still under investigation. We propose to apply tunable stress to the LaAlO3/SrTiO3 interface by while the sample is mounted in a scanning SQUID microscope, and observe how strain changes both the configuration of the more conducting paths and the magnitude of their conductivity enhancement. These studies may shed light on the relationship between strain, conductivity, and electronic structure in this system. [Preview Abstract] |
Wednesday, March 5, 2014 3:18PM - 3:30PM |
Q49.00003: Switching properties of superconducting micron-size channels in LaAlO3 /SrTiO3 hetero-structures Simon Hurand, Cheryl Feuillet-Palma, Johan Biscaras, Nicolas Reyren, Edouard Lesne, Nicolas Bergeal, Jerome Lesueur It has been shown that a superconducting two-dimensional electron gas (2DEG) could form at the interface between two insulators such as LaX(X$=$Al or Ti)O3 and SrTiO3 [1,2,3]. We present low temperature transport measurements on micron-size superconducting channels patterned in LaAlO3/SrTiO3 hetero-structures, whose properties can be modulated by field effect. The current-voltage characteristics measured as a function of gate voltage and temperature show a hysteretic behavior. We analyzed the switching and re-trapping currents for a large number of events in the framework of the Resistively and Capacitively Shunted Junction model (RCSJ). Standard deviation of the switching distribution is found to be constant with temperature, but gate-voltage dependent. The results are consistent with the description of the 2DEG as an inhomogeneous array [4] of moderately damped Josephson junctions in the quantum escape regime. [1] A. Ohtomo et al, Nature 427, 423 (2004), Nature 419, 378 (2002) [2] N. Reyren et al, Science 317, 1196 (2007) [3] J. Biscaras et al, Nature Communications 1,89 (2010), Phys. Rev. Lett. 108, 247004 (2012) [4] J. Biscaras et al, Nature Materials 12, 542--548 (2013) [Preview Abstract] |
Wednesday, March 5, 2014 3:30PM - 3:42PM |
Q49.00004: Coulomb blockade phenomena in confined LaAlO$_3$/SrTiO$_3$ nanowires Michelle Tomczyk, Guanglei Cheng, Shicheng Lu, Joshua Veazey, Mengchen Huang, Patrick Irvin, Sangwoo Ryu, Chang-Beom Eom, Jeremy Levy The LaAlO$_3$/SrTiO$_3$ interface hosts a rich variety of phenomena, including gate-tunable conductivity, ferromagnetism, and low-temperature superconductivity. Nanowires at the interface are fabricated with conductive AFM lithography; this flexible process allows complex nanostructures to be created to study the various phenomena at the interface. Here, tunneling barriers are created to confine a section of wire. Low temperature transport through these confined wires is gate-tunable, exhibiting superconductivity in the strong coupling regime and Coulomb blockade in the weak coupling regime. The Coulomb peaks exhibit interesting behavior in an external magnetic field. The peaks are insensitive to low fields; however, they begin to split and shift above a critical magnetic field. The curious splitting of each Coulomb peak above a critical field could provide insight into the fundamental magnetic, superconducting, and spin-orbit properties at the interface. [Preview Abstract] |
Wednesday, March 5, 2014 3:42PM - 3:54PM |
Q49.00005: Real-Time Transport Properties of Multiply-Connected LaAlO$_3$/SrTiO$_3$ Nanostructures Alexandre Gauthier, Patrick Irvin, Jeremy Levy Electronic nanostructures can be created at the LaAlO$_3$/SrTiO$_3$ interface using a conductive atomic force microscope technique\footnote{C. Cen, \textit{et al.}, Science \textbf{323}, 1026 (2009)}. These nanowires can be arranged into complex nanostructures such as photodetectors\footnote{P. Irvin, \textit{et al.}, Nature Photonics \textbf{4}, 849 (2010)} and single-electron transistors\footnote{G. Cheng, \textit{et al.}, Nature Nanotechnology \textbf{6}, 343 (2011)}. We have developed a way to characterize multi-terminal devices in real time. AC voltages at distinct frequencies are applied to every electrical contact for the device. Fourier analysis of the current response at each electrode allows the $\textit{N}$-terminal conductance matrix to be determined simultaneously. [Preview Abstract] |
Wednesday, March 5, 2014 3:54PM - 4:06PM |
Q49.00006: Anisotropic superconductivity of nanowires at LaAlO$_3$/SrTiO$_3$(110) heterointerface Jeremy Levy, Mengchen Huang, Guanglei Cheng, Patrick Irvin, Anil Annadi, Kalon Gopinadhan, A. Ariando, T. Venkatesan, Q. Zhang, Bo Gu, Seiji Yunoki, Sadamichi Maekawa A two-dimensional electron gas has recently been discovered at the interface of LaAlO$_3$ grown on the (110) surface of SrTiO$_3$.\footnote{A. Annadi, \textit{et al.}.\textit{Nature Commun.} \textbf{4}, 1838 (2013)} The conductivty of the 2DEG at this interface is anisotropic along different crystallographic directions. Using conducting AFM lithography we write interfacial nanowires along the (001) and (1-10) directions on 3-unit cell LaAlO$_3$/SrTiO$_3$(110). Similar to the anisotropic conductivity found in the normal state, we observe anisotropy of the superconducting properties of the two types of wire: the upper critical magnetic field of nanowires along the (001) direction is higher than those along (1-10) direction. This observation can be related to the anisotropic orbital binding of Ti and O atoms and the differences in the spin-orbit coupling along the two different directions. [Preview Abstract] |
Wednesday, March 5, 2014 4:06PM - 4:18PM |
Q49.00007: High-mobility sketched nanostructures at the Al$_2$O$_3$/SrTiO$_3$ interface Shicheng Lu, Sang Woon Lee, Guanglei Cheng, Feng Bi, Akash Levy, Mengchen Huang, Patrick Irvin, Roy G. Gordon, Jeremy Levy A two dimensional electron gas has recently been demonstrated at the interface between amorphous Al$_2$O$_3$ and TiO$_2$-terminated SrTiO$_3$ by atomic layer deposition (ALO/STO).\footnote{S. W. Lee, \textit{et al.}, Nano Lett. \textbf{12}, 4775 (2012).} Similar to LaAlO$_3$/SrTiO$_3$ heterostructrues, when the ALO thickness exceeds a critical thickness, the interface becomes conducting. By using a conducting atomic force microscope tip to control the metal-insulator transition at nanoscale dimensions, we are able to create nanostructures with exceptionally high mobility. Quasi-two-dimensional written structures exhibit Shubnikov de Haas oscillations and mobilities in excess of 2,000 cm$^2$/Vs. Furthermore, by decreasing the channel width to 10 nm width, the mobility becomes as high as 100,000 cm$^2$/Vs. [Preview Abstract] |
Wednesday, March 5, 2014 4:18PM - 4:30PM |
Q49.00008: Nanoscale control of oxide interface conduction in graphene-complex-oxide heterostructures Mengchen Huang, Sangwoo Ryu, Fereshte Ghahari, Giriraj Jnawali, Jayakanth Ravichandran, Patrick Irvin, Philip Kim, Chang-Beom Eom, Jeremy Levy Graphene is a promising material for high-speed optoelectronic devices such as THz modulators and detectors. Recently, broadband THz emission and detection can be achieved with nanostructures at the LaAlO$_3$/SrTiO$_3$ interface \footnote{Y. Ma, \textit{et al.}, \textit{Nano Lett.} \textbf{13}, 2284 (2013)}. We have mechanically exfoliated single layer and multilayer graphene on top of 3.4 unit cell LaAlO$_3$/SrTiO$_3$ and successfully sketched nanowires in the 2DEG underneath graphene using conductive AFM lithgraphy \footnote{C. Cen, \textit{et al.}, \textit{Nat. Mater.} \textbf{7}, 298 (2008)}. Raman and AFM investigations confirm that the graphene quality and surface morphology remain unaltered by the writing process. These first experimental demonstrations of integrating graphene and LaAlO$_3$/SrTiO$_3$ are promising for future DC-THz photonic applications. [Preview Abstract] |
Wednesday, March 5, 2014 4:30PM - 4:42PM |
Q49.00009: Ionic Liquid/Solid Double Gate Modulation of the LaAlO$_{3}$/SrTiO$_{3}$ Interfacial Electron Gas Zhuoyu Chen, Hongtao Yuan, Yanwu Xie, Di Lu, Yasuyuki Hikita, Christopher Bell, Harold Hwang An intriguing combination of properties including high electron mobility, superconductivity, ferromagnetism, and strong spin-orbit coupling has been observed at the LaAlO$_{3}$/SrTiO$_{3}$ (LAO/STO) interfacial quasi-two-dimensional electron gas (q2DEG). To experimentally clarify the electronic band structure of the q2DEG and how these properties evolve with external tuning by the electric field effect is a key challenge. Here we study the transport properties of the q2DEG in a double-gate field-effect transistor geometry utilizing an ionic liquid as the top gate dielectric, and the STO substrate as the back gate. A systematic carrier density and mobility modulation over a previously unobtained parameter range is achieved, providing a clear picture of electrostatic gating in this system. Changes in the carrier density, mobility, and conductivity strongly suggest the filling of heavy- and light- mass subbands in the quantum well as the top gate voltage is increased with respect to the q2DEG. When the heavier-mass electron subbands dominate the conductivity, signatures of negative electronic compressibility were observed, implying the presence of a tunable strong Rashba spin-orbit splitting in the anisotropic heavier-mass bands at this heterointerface. [Preview Abstract] |
Wednesday, March 5, 2014 4:42PM - 4:54PM |
Q49.00010: Nanoscale control of the LaAlO$_3$/SrTiO$_3$ metal-insulator transition using a self-assembled monolayer of APTES Jianan Li, Mengcheng Huang, Patrick Irvin, Jeremy Levy, Sangwoo Ryu, Chang-Beom Eom, Daniel Eichelsdoerfer, Keith Brown, Chad Mirkin Nanoscale control over the metal-insulator transition at oxide interfaces represents an exciting opportunity for science and technology. Nanostructures created from 3-unit-cell LaAlO$_3$/SrTiO$_3$ heterostructures via a conductive AFM technique typically decay within hours under ambient conditions, representing a challenge for some technologies. By chemically modifying the top LaAlO$_3$ surface with a self-assembled monolayer of (3-Aminopropyl)triethoxysilane (APTES), normally conductive 4-unit-cell LaAlO$_3$/SrTiO$_3$ can be made highly insulating. The APTES layer can be locally patterned, revealing a highly stable conductive nanoregion. Four-terminal measurements show that nanowires created by selective desorption of APTES remain conductive indefinitely under ambient conditions. The results suggest a robust mechanism for creating long-lived nanostructures at oxide interfaces. [Preview Abstract] |
Wednesday, March 5, 2014 4:54PM - 5:06PM |
Q49.00011: ABSTRACT WITHDRAWN |
Wednesday, March 5, 2014 5:06PM - 5:18PM |
Q49.00012: Tunning the conductivity at \textit{n} --type LAO/STO heterointerface by Au(111) nanoparticles Tra Vu Thanh The observation of a two-dimensional electron gas (2DEG) at the LaAlO$_{3}$/SrTiO$_{3}$ heterostructure is a well-known example of interface physics. While most studies are aiming at exploring new interfaces by combining different materials, another key to real device applications is the interface control through external stimuli. In this paper, we propose a generic approach to use Au(111) nanoparticles on the LAO/STO interface as an external stimules in pumping the free electrons into the 2DEG of the LAO/STO heterointerface. Our results show that the conductivity of the LAO/STO interface increases with the density and size of Au nanoparticles. In order to reveal the insight, the change of the interface band structure was investigated by combining both the ferroelectric pattern assisted x-ray photoelectron spectroscopy and the scanning tunneling spectroscopy with modeling calculations. This study opens a new venue of controlling the conduction of complex oxide interfaces. [Preview Abstract] |
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