Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session D34: Focus Session: Interfaces in Complex Oxides - Photo and Electric Field Induced Devices |
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Sponsoring Units: DMP Chair: Peter Abbamonte, University of Illinois at Urbana-Champaign Room: C141 |
Monday, March 21, 2011 2:30PM - 3:06PM |
D34.00001: Band profiles of Mott-insulator/band-insulator heterointerfaces revealed by photocurrent and electromodulation spectroscopies Invited Speaker: Heterointerfaces of Mott insulators provide a good laboratory to explore unprecedented electronic states induced by the strong electron correlation. Although a number of intriguing phenomena have been reported so far, their fundamental origins have not been fully addressed yet. This is partly because the interface band profile, which is one of the most basic knowledge to understand the interface electronic states, is still left to be unveiled. In this study, we have investigated in detail the interface band profiles of Mott insulators employing photocurrent and electromodulation spectroscopies as well as the conventional current-voltage and capacitance-voltage characterizations. We chose $p$-type (LaMnO$_{3}$ and La$_{2}$CuO$_{4}$) and $n$-type (SrMnO$_{3}$ and Sm$_{2}$CuO$_{4}$) as the Mott insulators and these are epitaxially connected to Nb doped SrTiO$_{3}$ (electron-doped band insulator). The photocurrent action spectra for these heterojunctions showed negligibly-small band reconstruction as well as the existence of band bending and discontinuity in the Mott insulators, which are of no salient discrepancy with the rigid-band picture valid in the interface of conventional semiconductors~[1]. However, the electromodulation spectra clearly indicate the band reconstruction in the Mott insulators~[2]. The results mean that the rigid-band picture is valid in the low carrier-density regime even in Mott-insulator/band-insulator interfaces, but the intentional charge modulation leads the electron correlation effect in the Mott insulators. This work was done in collaboration with A. Sawa, J. Fujioka, M. Kawasaki and Y. Tokura.\\[4pt] [1]~M. Nakamura~\textit{et al.},~Phys.~Rev.~B~\textbf{82},~201101(R)~(2010)\\[0pt] [2]~M. Nakamura~\textit{et al.},~Phys.~Rev.~B~\textbf{75},~155103~(2007). [Preview Abstract] |
Monday, March 21, 2011 3:06PM - 3:18PM |
D34.00002: Mechanisms for the enhancement of the lateral photovoltage in perovskite heterostructures Kui-juan Jin, Chen Ge, Huibin Lu, Guozhen Yang The mechanisms for greatly enhanced lateral photovoltaic effect in the perovskite oxide heterostructures are studied by solving \textit{time-dependent} two-dimensional drift-diffusion equations self-consistently. By our calculations, we find that the lateral photovoltage of $p$ type material is larger than that of $n$ type material owing to the larger drift electric field induced in the $p$ type material than that in the $n$ type material. Moreover, the built-in electric field at the interface between the thin film and substrate can also enhance the lateral photovoltage. The above two mechanisms can well explain one-order-of-magnitude enhancement of the LPV in the perovskite heterostructures. In addition, we find that the materials with larger mobility ratio have stronger Dember effect. Such an understanding of the mechanisms for the enhancement of lateral photovoltage in oxide heterostructures should be useful in further designing of the structures of position-sensitive detectors and new THz sources. [Preview Abstract] |
Monday, March 21, 2011 3:18PM - 3:30PM |
D34.00003: Electronic Transport in Ion Gel-Gated Strontium Titanate Men Young Lee, James R. Williams, David Goldhaber-Gordon, Sipei Zhang, C. Daniel Frisbie, Bharat Jalan, Junwoo Son, Susanne Stemmer In recent years much attention has been focused on the structure and properties of two-dimensional electron liquids (2DEL) in complex oxide heterostrucutres and delta- doped layers. We report on the fabrication and measurements of mesoscopic devices of metal oxides, with focus given to an electric field-induced 2DEL at the surface of undoped strontium titanate (STO). We describe the design and fabrication of field- effect structures, gated with an ionic gel, and show the measurements of induced swings of charge carrier density in STO. Other transport properties of the 2DEL are studied by magneto-transport measurements at low temperature. [Preview Abstract] |
Monday, March 21, 2011 3:30PM - 3:42PM |
D34.00004: Origin of Electrical Conduction in Domain Walls of BiFeO${_3}$ Thin Films James Lee, Anoop Damodaran, Lane Martin, Peter Abbamonte, Helen He, Ramamoorthy Ramesh BiFeO${_3}$ thin films grown on DyScO${_3}$ substrates unexpectedly exhibit metallic electrical conduction at ferroelectric (FE) domain walls (DWs). Resonant x-ray scattering near Fe L and O K absorption edges was used to probe the electronic structure of these films. In-plane wavevectors of resonant Fe edge magnetic scattering, and non-resonant Cu K $\alpha $ diffraction peaks near the (0, 0, 1) BiFeO${_3}$ Bragg peak, match the domain period observed by PFM. Fe edge scattering intensifies as the beam energy is tuned to Fe 2p $\to$ ligand-3d transitions. No O K charge scattering is observed. These results suggest that metallic conduction does not arise from charge build- up at the DWs from FE polarization discontinuities, but from the bandgap closing near DWs as the crystal symmetry changes from rhombohedral-like in the domain bulk to higher-symmetries. [Preview Abstract] |
Monday, March 21, 2011 3:42PM - 3:54PM |
D34.00005: Sketched ferroelectric single-electron transistor Guanglei Cheng, Pablo Siles, Feng Bi, Cheng Cen, Daniela Bogorin, Chung Wung Bark, Chad Folkman, Jae-Wan Park, Chang-Beom Eom, Gilberto Medeiros-Ribeiro, Jeremy Levy Oxide heterostructures formed from ultrathin layers of LaAlO$_{3}$ grown on TiO$_{2}$-terminated SrTiO$_{3}$, combined with a reversible nanoscale patterning technique, provide a versatile platform for nanoscale control at the single-electron limit. Here we demonstrate the creation and characterization of ``sketched'' single-electron transistors made from ultrasmall (1-2 nm) quantum dots. Shell filling from N=0 up to N=2 electrons by single-electron tunneling is observed. Resonant tunneling can be controlled in a deterministic and non-volatile fashion by altering the ferroelectric polarization within the SrTiO$_{3}$ tunnel barrier. These single-electron devices may find use as nanoscale hybrid piezoelectric/charge sensors, and as elemental building blocks for solid-state quantum computation and quantum simulation platforms. [Preview Abstract] |
Monday, March 21, 2011 3:54PM - 4:06PM |
D34.00006: Characterizing Interfacial Bipolar Resistive Switches at Low Temperatures Stephen Tsui Bipolar resistive switching has continued to be a topic of interest for many years because of the phenomenon's potential for memory device applications. Typically, a voltage pulse is applied to a metal-oxide sandwich structure, which drives the sample into a nonvolatile high or low resistance state depending upon the pulse polarity. A great deal of research has already been performed on a diverse array of materials with several different characteristics. However, few systematic investigations have been carried out at low temperature, which may have application to ``cryo-memory.'' In this work, we compare the room temperature and low temperature behaviors of switches formed at the interfaces between a silver electrode and CeO$_{2}$, Al$_{2}$O$_{3}$, and Pr$_{0.7}$Ca$_{0.3}$MnO$_{3}$, respectively. We investigate the performance of the switching in response to temperature change and characterize the electronic transport at the interfaces in order to identify the dominant physical processes at these various temperatures. [Preview Abstract] |
Monday, March 21, 2011 4:06PM - 4:18PM |
D34.00007: Role of the surface in writing, erasing and maintaining nanostructures at the LaAlO$_{3}$/SrTiO$_{3}$ interface Feng Bi, Daniela F. Bogorin, Cheng Cen, Jeremy Levy, Chung Wung Bark, Jae-Wan Park, Chang-Beom Eom Nanoscale control of the metal-insulator transition in LaAlO$_{3}$/SrTiO$_{3}$ heterostructures can be achieved using local voltages applied by a conducting AFM probe. The mechanism is believed to be governed by a ``water cycle'' in which the surface is locally charged via hydrogen passivation, resulting in high-resolution modulation doping of the LaAlO$_{3}$/SrTiO$_{3}$ interface.\footnote{F. Bi et al., Appl. Phys. Lett.97, 173110 (2010)} A Kelvin probe image method is applied to study how water content in the gas environment influences such charge writing. Persistence tests are performed, in which the long-term behavior is studied by keeping the AFM-written nanostructures (nanowire and sketch FET\footnote{C.Cen et al., Science, 323, 1026 (2009)}) in different ambient environments. The self-erasure process is particularly obvious in moisture environments, but is slowed greatly in dry inert gas and can be even halted under modest vacuum conditions ($\sim$10$^{-3}$ Torr). [Preview Abstract] |
Monday, March 21, 2011 4:18PM - 4:30PM |
D34.00008: Electric field-tuning of the magneto-transport of superconducting LaAlO$_3$/SrTiO$_3$ interfaces Stefano Gariglio, Nicolas Reyren, Andrea D. Caviglia, Claudia Cancellieri, Toni Schneider, Jean-Marc Triscone LaAlO$_3$/SrTiO$_3$ interfaces display a complex phase diagram that can be explored by an electric field [1,2]. Using transport measurements in magnetic fields for different doping levels, we have characterized the superconducting phase diagram in three dimensions (temperature, electric and magnetic fields). Analyses of the anisotropy for parallel and perpendicular magnetic fields [3] reveal a two-dimensional superconducting state for all doping levels. Magneto-resistances in perpendicular fields present hallmarks of superconductor-insulator and superconductor-metal transitions depending on the doping level. We will discuss scaling analyses of the magnetic field-tuned transitions and the role of fluctuations and disorder in this two-dimensional superconductor. \\[4pt] [1] N. Reyren et al. Science 317, 1196 (2007).\\[0pt] [2] A. Caviglia et al. Nature 456, 624 (2008).\\[0pt] [3] N. Reyren et al. Appl. Phys. Lett. 94, 112506 (2009). [Preview Abstract] |
Monday, March 21, 2011 4:30PM - 4:42PM |
D34.00009: Cooper Pair Writing at the LaAlO$_{3}$/SrTiO$_{3}$ Interface Cheng Cen, Daniela F. Bogorin, Chung Wung Bark, Chad M. Folkman, Chang-Beom Eom, Jeremy Levy Superconducting semiconductors offer unique ways to exert electrostatic control over macroscopic quantum phases. The recently demonstrated nanoscale control over conductivity at the LaAlO$_{3}$/SrTiO$_{3}$ interface raises the question of whether nanoscale control over superconducting phases can be realized. Here we report low-temperature magnetotransport experiments on structures defined with nanoscale precision at the LaAlO$_{3}$/SrTiO$_{3}$ interface. A quantum phase transition is observed that is associated with the formation of Cooper pairs, but a finite resistance is observed at the lowest temperatures. Higher mobility interfaces exhibit larger Ginsburg-Landau coherence lengths, a stronger suppression of pairing by magnetic field as well as Shubnikov-de Haas oscillations. Cooper pair localization, spin-orbit coupling, and finite-size effects may factor into an explanation for some of the unusual properties observed. [Preview Abstract] |
Monday, March 21, 2011 4:42PM - 4:54PM |
D34.00010: Electric and magnetic field control of superconducting transition at the LaAlO$_{3}$/SrTiO$_{3}$ heterointerface Dmitriy Dikin, Manan Mehta, Venkat Chandrasekhar, Chung Wung Bark, Chad Folkman, Chang-Beom Eom We report on detailed measurements of the normal state-superconducting phase transition of the two-dimensional electron gas that develops at the LAO/STO interface as a function of gate voltage and magnetic field. We will discuss the specifics of the R versus T and the T-H phase diagrams for this superconductor and the potential origin of observed dissipation and hysteretic behavior. These data are analyzed in connection with magnetoresistance and Hall measurements. [Preview Abstract] |
Monday, March 21, 2011 4:54PM - 5:06PM |
D34.00011: Metal-insulator transition at the interface of LaAlO$_3$ /SrTiO$_3$ induced by H$_2$O adsorption Yun Li, Jaejun Yu We investigated the adsorption configurations at various H$_2$O coverages on the AlO$_2$ surface of n-type interface of 3 unit cell layers of LaAlO$_3$ (LAO) overlayer on SrTiO$_3$ (001) (STO) and the effects on the electronic properties at the interface by carrying out density-functional-theory calculations. For 0.25 monolayer (ML) and 0.5 ML coverages of H$_2$O the dissociation processes are barrierless. While for 1 ML coverage the mixing adsorption configuration comprising 0.5 ML molecular and 0.5 ML dissociated H$_2$O is most stable and the dissociation from fully molecular adsorption has to overcome 1 eV barrier. Insulator-metal transition at the n-type interface of (LAO)3/STO occurs as the coverage of dissociated H$_2$O reaches to 0.5ML. Insulator-metal transition at the interface can be realized by two ways: (1) changing H$_2$O coverage of from less than 0.5ML to equal to 0.5ML; (2) fixing H$_2$O coverage at 1ML and converting the adsorption configuration form fully molecular adsorption to mixing (0.5:0.5) adsorption. The second scheme can be utilized to realizing single-electron controlled nanoscale memory and switch. [Preview Abstract] |
Monday, March 21, 2011 5:06PM - 5:18PM |
D34.00012: GHz operation of LaAlO$_{3}$/ SrTiO$_{3}$-based transistor Patrick Irvin, Mengchen Huang, Jeremy Levy, Chung Wung Bark, Chad M. Folkman, Chang-Beom Eom Local modification of the metal-insulator transition of the LaAlO$_{3}$ /SrTiO$_{3}$ interface with a conducting-atomic force microscope (c-AFM) has resulted in a variety of electrical\footnote{C. Cen, S. Thiel, J. Mannhart, and J. Levy, Science \textbf{323}, 1026 (2009).} and photonic\footnote{P. Irvin, Y. Ma, D. F. Bogorin, C. Cen, C. W. Bark, C. M. Folkman, C.-B. Eom, and J. Levy, Nature Photonics advanced online publication, 14 Nov.2010 (DOI 10.1038/nphoton.2010.238)} devices. Using a heterodyne measurement technique, we show that a sketch-based, nanoscale transistor (``SketchFET'') can operate at frequencies in excess of 1 GHz. This demonstration of GHz functionality opens the door for new applications for oxide-based, rewritable nanoscale devices. [Preview Abstract] |
Monday, March 21, 2011 5:18PM - 5:30PM |
D34.00013: Nanoscale control at the LaAlO$_{3}$/SrTiO$_{3}$ Interface grown on LSAT Daniela Bogorin, Cheng Cen, Chung Wung Bark, Chang Beom Eom, Jeremy Levy The two-dimensional electron gas (2DEG) that forms at the interface between two semiconductors or between a semiconductor and oxide is currently the basis for some of the most useful electronic devices. We are able to control the 2DEG interface between LaAlO$_{3}$/SrTiO$_{3}$ with nanoscale precision and create transistors, nanodiodes and other nanostructures. Future scaling of oxide nanoelectronics requires scaling to wafer sizes larger than what can be provided from SrTiO$_{3}$. (LaAlO$_{3})_{0.3}$--(Sr$_{2}$AlTaO$_{3})_{0.7}$ (LSAT) substrates can allow for coherently strained LaAlO$_{3}$/SrTiO$_{3}$ heterostructures to be created. A sharp insulator to metal transition occurs at 8 uc LaAlO$_{3}$ thicknesses, in contrast to what is observed for unstrained SrTiO$_{3}$ substrates. We describe the properties of nanoscale structures created at the 2DEG interface of LaAlO$_{3}$/SrTiO$_{3}$ grown on LSAT wafers and compare them with structures grown on bulk SrTiO$_{3}$ substrates. [Preview Abstract] |
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