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Guanglei Cheng,
Joshua P. Veazey,
Patrick Irvin,
Cheng,
Daniela F,
Feng Bi,
Mengchen Huang,
Shicheng Lu,
Chung-Wung Bark,
Sangwoo Ryu,
Kwang-Hwan Cho, Chang-Beom Eom,
Jeremy Levy
[show abstract]
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ABSTRACT: The oxide heterostructure LaAlO3/SrTiO3 supports a two-dimensional electron
liquid with a variety of competing phases including magnetism,
superconductivity and weak antilocalization due to Rashba spin-orbit coupling.
Further confinement of this 2D electron liquid to the quasi-one-dimensional
regime can provide insight into the underlying physics of this system and
reveal new behavior. Here we describe magnetotransport experiments on narrow
LaAlO3/SrTiO3 structures created by a conductive atomic force microscope
lithography technique. Four-terminal local transport measurements on
~10-nm-wide Hall bar structures yield longitudinal resistances that are
comparable to the resistance quantum h/e2 and independent of the channel
length. Large nonlocal resistances (as large as 10^4 ohms) are observed in some
but not all structures with separations between current and voltage that are
large compared to the 2D mean-free path. The nonlocal transport is strongly
suppressed by the onset of superconductivity below ~200 mK. The origin of these
anomalous transport signatures is not understood, but may arise from coherent
transport defined by strong spin-orbit coupling and/or magnetic interactions.
03/2013;
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[show abstract]
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ABSTRACT: LaAlO3/SrTiO3 heterostructures are known to exhibit a sharp, hysteretic
metal-insulator transition (MIT) with large enhanced capacitance near
depletion. To understand the physical origin of this behavior, the
electromechanical response of top-gated LaAlO3/SrTiO3 heterostructures is
probed using two simultaneous measurement techniques: piezoforce microscopy
(PFM) and capacitance spectroscopy. PFM measurements reveal local variations in
the hysteretic response, which is directly correlated with capacitance
measurements. The enhanced capacitance at the MIT is linked to
charging/discharging dynamics of nanoscale conducting islands, which are
revealed through PFM imaging and time-resolved capacitance and piezoresponse
measurements.
02/2013;
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[show abstract]
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ABSTRACT: Nanoscale control of the metal-insulator transition at the interface between LaAlO(3) and SrTiO(3) provides a pathway for reconfigurable, oxide-based nanoelectronics. Four-terminal transport measurements of LaAlO(3)/SrTiO(3) nanowires at room temperature (T=300 K) reveal an equivalent 2D Hall mobility greatly surpassing that of bulk SrTiO(3) and approaching that of n-type Si nanowires of comparable dimensions. This large enhancement of mobility is relevant for room-temperature device applications.
Nano Letters 01/2013; · 13.20 Impact Factor
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Joshua P. Veazey,
Guanglei Cheng,
Patrick Irvin,
Cheng Cen,
Daniela F. Bogorin,
Feng Bi,
Mengchen Huang,
Chung-Wung Bark,
Sangwoo Ryu,
Kwang-Hwan Cho, Chang-Beom Eom,
Jeremy Levy
[show abstract]
[hide abstract]
ABSTRACT: We report superconductivity in quasi-1D nanostructures created at the
LaAlO3/SrTiO3 interface. Nanostructures having line widths w~10 nm are formed
from the parent two-dimensional electron liquid using conductive atomic force
microscope lithography. Nanowire cross-sections are small compared to the
superconducting coherence length in LaAlO3/SrTiO3 (w<<xi~100 nm), placing them
in the quasi-1D regime. Broad superconducting transitions with temperature and
finite resistances in the superconducting state well below Tc~200 mK are
observed. V-I curves show switching between the superconducting and normal
states that are characteristic of superconducting nanowires. The four-terminal
resistance in the superconducting state shows an unusual dependence on the
current path, varying by as much as an order of magnitude.
10/2012;
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ABSTRACT: Strong interest in resistive switching phenomena is driven by a possibility to develop electronic devices with novel functional properties not available in conventional systems. Bistable resistive devices are characterized by two resistance states that can be switched by an external voltage. Recently, memristors-electric circuit elements with continuously tunable resistive behavior-have emerged as a new paradigm for nonvolatile memories and adaptive electronic circuit elements. Employment of memristors can radically enhance the computational power and energy efficiency of electronic systems. Most of the existing memristor prototypes involve transition metal oxide resistive layers where conductive filaments formation and/or the interface contact resistance control the memristive behavior. In this paper, we demonstrate a new type of memristor that is based on a ferroelectric tunnel junction, where the tunneling conductance can be tuned in an analogous manner by several orders of magnitude by both the amplitude and the duration of the applied voltage. The ferroelectric tunnel memristors exhibit a reversible hysteretic nonvolatile resistive switching with a resistance ratio of up to 10(5) % at room temperature. The observed memristive behavior is attributed to the field-induced charge redistribution at the ferroelectric/electrode interface, resulting in the modulation of the interface barrier height.
Nano Letters 10/2012; · 13.20 Impact Factor
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[show abstract]
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ABSTRACT: The hysteretic piezoelectric response in LaAlO3/SrTiO3 heterostructures can
provide important insights into the mechanism for interfacial conductance and
its metastability under various conditions. We have performed a variety of
nonlocal piezoelectric force microscopy experiments on 3 unit cell
LaAlO3/SrTiO3 heterostructures. A hysteretic piezoresponse is observed under
various environmental and driving conditions. The hysteresis is suppressed when
either the sample is placed in vacuum or the interface is electrically
grounded. We present a simple physical model which can account for the observed
phenomena.
08/2012;
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Peng Gao,
Christopher T Nelson,
Jacob R Jokisaari,
Yi Zhang,
Seung-Hyub Baek,
Chung Wung Bark,
Enge Wang,
Yuanming Liu,
Jiangyu Li, Chang-Beom Eom,
Xiaoqing Pan
[show abstract]
[hide abstract]
ABSTRACT: Nonvolatile ferroelectric random-access memory uses ferroelectric thin films to save a polar state written by an electric field that is retained when the field is removed. After switching, the high energy of the domain walls separating regions of unlike polarization can drive backswitching resulting in a loss of switched domain volume, or in the case of very small domains, complete retention loss.
Advanced Materials 02/2012; 24(8):1106-10. · 13.88 Impact Factor
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[show abstract]
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ABSTRACT: In this work, epitaxial (001) BiFeO3 thin films were deposited on SrTiO3 and TbScO3 single-crystal substrates and analyzed with high-resolution x-ray diffraction—reciprocal space mapping. A basic method was developed to extract structural details of the as-grown BiFeO3 film, including (i) epitaxial strain, (ii) ferroelastic domains, and (iii) lattice rotations. After demonstrating the method, extrinsic distortions at vertical twin walls were determined for specific BiFeO3 heterostructures. A relatively large distortion (0.20° ± 0.08°) was measured in a multidomain (12) and incoherent film, while a nearly intrinsic distortion (0.04° ± 0.03°) was measured in a two-domain coherent film. This work offers insights into the structure of multiferroic BiFeO3 thin films with a general approach that is appropriate for low symmetry epitaxial heterostructures.
Journal of Materials Research. 11/2011; 26(22):2844 - 2853.
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Christopher T Nelson,
Peng Gao,
Jacob R Jokisaari,
Colin Heikes,
Carolina Adamo,
Alexander Melville,
Seung-Hyub Baek,
Chad M Folkman,
Benjamin Winchester,
Yijia Gu,
Yuanming Liu,
Kui Zhang,
Enge Wang,
Jiangyu Li,
Long-Qing Chen, Chang-Beom Eom,
Darrell G Schlom,
Xiaoqing Pan
[show abstract]
[hide abstract]
ABSTRACT: The utility of ferroelectric materials stems from the ability to nucleate and move polarized domains using an electric field. To understand the mechanisms of polarization switching, structural characterization at the nanoscale is required. We used aberration-corrected transmission electron microscopy to follow the kinetics and dynamics of ferroelectric switching at millisecond temporal and subangstrom spatial resolution in an epitaxial bilayer of an antiferromagnetic ferroelectric (BiFeO(3)) on a ferromagnetic electrode (La(0.7)Sr(0.3)MnO(3)). We observed localized nucleation events at the electrode interface, domain wall pinning on point defects, and the formation of ferroelectric domains localized to the ferroelectric and ferromagnetic interface. These results show how defects and interfaces impede full ferroelectric switching of a thin film.
Science 11/2011; 334(6058):968-71. · 31.20 Impact Factor
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Ji Young Jo,
Pice Chen,
Rebecca J Sichel,
Seung-Hyub Baek,
Ryan T Smith,
Nina Balke,
Sergei V Kalinin,
Martin V Holt,
Jörg Maser,
Kenneth Evans-Lutterodt, Chang-Beom Eom,
Paul G Evans
[show abstract]
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ABSTRACT: Domains of remnant polarization can be written into ferroelectrics with nanoscale precision using scanning probe nanolithography techniques such as piezoresponse force microscopy (PFM). Understanding the structural effects accompanying this process has been challenging due to the lack of appropriate structural characterization tools. Synchrotron X-ray nanodiffraction provides images of the domain structure written by PFM into an epitaxial Pb(Zr,Ti)O(3) thin film and simultaneously reveals structural effects arising from the writing process. A coherent scattering simulation including the superposition of the beams simultaneously diffracted by multiple mosaic blocks provides an excellent fit to the observed diffraction patterns. Domains in which the polarization is reversed from the as-grown state have a strain of up to 0.1% representing the piezoelectric response to unscreened surface charges. An additional X-ray microdiffraction study of the photon-energy dependence of the difference in diffracted intensity between opposite polarization states shows that this contrast has a crystallographic origin. The sign and magnitude of the intensity contrast between domains of opposite polarization are consistent with the polarization expected from PFM images and with the writing of domains through the entire thickness of the ferroelectric layer. The strain induced by writing provides a significant additional contribution to the increased free energy of the written domain state with respect to a uniformly polarized state.
Nano Letters 08/2011; 11(8):3080-4. · 13.20 Impact Factor
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Sophie A Harrington,
Junyi Zhai,
Sava Denev,
Venkatraman Gopalan,
Haiyan Wang,
Zhenxing Bi,
Simon A T Redfern,
Seung-Hyub Baek,
Chung W Bark, Chang-Beom Eom,
Quanxi Jia,
Mary E Vickers,
Judith L Macmanus-Driscoll
[show abstract]
[hide abstract]
ABSTRACT: Ferroelectric materials are used in applications ranging from energy harvesting to high-power electronic transducers. However, industry-standard ferroelectric materials contain lead, which is toxic and environmentally unfriendly. The preferred alternative, BaTiO(3), is non-toxic and has excellent ferroelectric properties, but its Curie temperature of ∼130 °C is too low to be practical. Strain has been used to enhance the Curie temperature of BaTiO(3) (ref. 4) and SrTiO(3) (ref. 5) films, but only for thicknesses of tens of nanometres, which is not thick enough for many device applications. Here, we increase the Curie temperature of micrometre-thick films of BaTiO(3) to at least 330 °C, and the tetragonal-to-cubic structural transition temperature to beyond 800 °C, by interspersing stiff, self-assembled vertical columns of Sm(2)O(3) throughout the film thickness. The columns, which are 10 nm in diameter, strain the BaTiO(3) matrix by 2.35%, forcing it to maintain its tetragonal structure and resulting in the highest BaTiO(3) transition temperatures so far.
Nature Nanotechnology 07/2011; 6(8):491-5. · 27.27 Impact Factor
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Advanced Materials 04/2011; 23(14):1621-5. · 13.88 Impact Factor
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Christopher T Nelson,
Benjamin Winchester,
Yi Zhang,
Sung-Joo Kim,
Alexander Melville,
Carolina Adamo,
Chad M Folkman,
Seung-Hyub Baek, Chang-Beom Eom,
Darrell G Schlom,
Long-Qing Chen,
Xiaoqing Pan
[show abstract]
[hide abstract]
ABSTRACT: The polarization of the ferroelectric BiFeO(3) sub-jected to different electrical boundary conditions by heterointerfaces is imaged with atomic resolution using a spherical aberration-corrected transmission electron microscope. Unusual triangular-shaped nanodomains are seen, and their role in providing polarization closure is understood through phase-field simulations. Heterointerfaces are key to the performance of ferroelectric devices, and this first observation of spontaneous vortex nanodomain arrays at ferroelectric heterointerfaces reveals properties unlike the surrounding film including mixed Ising-Néel domain walls, which will affect switching behavior, and a drastic increase of in-plane polarization. The importance of magnetization closure has long been appreciated in multidomain ferromagnetic systems; imaging this analogous effect with atomic resolution at ferroelectric heterointerfaces provides the ability to see device-relevant interface issues. Extension of this technique to visualize domain dynamics is envisioned.
Nano Letters 02/2011; 11(2):828-34. · 13.20 Impact Factor
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Yi Zhang,
Christopher T. Nelson,
Sanghan Lee,
Jianyi Jiang,
Chung Wung Bark,
Jeremy D. Weiss,
Chiara Tarantini,
Chad M. Folkman,
Seung-Hyub Baek,
Eric E. Hellstrom,
David C. Larbalestier, Chang-Beom Eom,
Xiaoqing Pan
[show abstract]
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ABSTRACT: We report the structure and chemistry of the self-assembled oxide nanopillars that form in superconducting Co-doped BaFe2As2 thin film grown by pulsed laser deposition. The oxide nanopillars consist of a BaFeO2 phase, form epitaxially on the SrTiO3 template, and grow coherently with the BaFe2As2 film. The nanopillars are square with a uniform size of 4–5 nm, which is close to twice the superconducting coherence length. Despite a volume content of ∼ 5%, the nanopillars do not degrade the structural quality of the BaFe2As2 matrix. Indeed the nanopillars provide exceptionally strong vortex pinning and high critical current density due to the very close correlation of pillar and vortex core diameters.
Applied Physics Letters 01/2011; 98(4):042509-042509-3. · 3.84 Impact Factor
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Guanglei Cheng,
Pablo F Siles,
Feng Bi,
Cheng Cen,
Daniela F Bogorin,
Chung Wung Bark,
Chad M Folkman,
Jae-Wan Park, Chang-Beom Eom,
Gilberto Medeiros-Ribeiro,
Jeremy Levy
[show abstract]
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ABSTRACT: Devices that confine and process single electrons represent an important scaling limit of electronics. Such devices have been realized in a variety of materials and exhibit remarkable electronic, optical and spintronic properties. Here, we use an atomic force microscope tip to reversibly 'sketch' single-electron transistors by controlling a metal-insulator transition at the interface of two oxides. In these devices, single electrons tunnel resonantly between source and drain electrodes through a conducting oxide island with a diameter of ∼1.5 nm. We demonstrate control over the number of electrons on the island using bottom- and side-gate electrodes, and observe hysteresis in electron occupation that is attributed to ferroelectricity within the oxide heterostructure. These single-electron devices may find use as ultradense non-volatile memories, nanoscale hybrid piezoelectric and charge sensors, as well as building blocks in quantum information processing and simulation platforms.
Nature Nanotechnology 01/2011; 6(6):343-7. · 27.27 Impact Factor
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ABSTRACT: Ferroelectric materials are characterized by a spontaneous polarization, which can be reoriented with an applied electric field. The switching between polarized domains is mediated by nanoscale defects. Understanding the role of defects in ferroelectric switching is critical for practical applications such as non-volatile memories. This is especially the case for ferroelectric nanostructures and thin films in which the entire switching volume is proximate to a defective surface. Here we report the nanoscale ferroelectric switching of a tetragonal PbZr(0.2)Ti(0.8)O(3) thin film under an applied electric field using in situ transmission electron microscopy. We found that the intrinsic electric fields formed at ferroelectric/electrode interfaces determine the nucleation sites and growth rates of ferroelectric domains and the orientation and mobility of domain walls, whereas dislocations exert a weak pinning force on domain wall motion.
Nature Communications 01/2011; 2:591. · 7.40 Impact Factor
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[show abstract]
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ABSTRACT: Nanoscale control of the metal-insulator transition in LaAlO3/SrTiO3 heterostructures can be achieved using local voltages applied by a conductive atomic force microscope (c-AFM) probe. One proposed mechanism for such process involves adsorbed H2O which dissociates into OH− and H+ which are then selectively removed by a biased AFM probe. To test this mechanism, writing and erasing experiments are performed in a vacuum AFM using various gas mixtures. Writing ability is suppressed in those environments where H2O is not present. The self-erasure process in air can be strongly suppressed by creating a modest vacuum or replacing the humid air with dry inert gas. These experiments provide strong constraints for theories of both the writing process as well as the origin of interfacial conductance.
Applied Physics Letters 10/2010; 97(17):173110-173110-3. · 3.84 Impact Factor
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ABSTRACT: Nanophotonic devices seek to generate, guide, and/or detect light using structures whose nanoscale dimensions are closely tied to their functionality. Semiconducting nanowires, grown with tailored optoelectronic properties, have been successfully placed into devices for a variety of applications. However, the integration of photonic nanostructures with electronic circuitry has always been one of the most challenging aspects of device development. Here we report the development of rewritable nanoscale photodetectors created at the interface between LaAlO3 and SrTiO3. Nanowire junctions with characteristic dimensions 2-3 nm are created using a reversible AFM writing technique. These nanoscale devices exhibit a remarkably high gain for their size, in part because of the large electric fields produced in the gap region. The photoconductive response is gate-tunable and spans the visible-to-near-infrared regime. The ability to integrate rewritable nanoscale photodetectors with nanowires and transistors in a single materials platform foreshadows new families of integrated optoelectronic devices and applications. Comment: 5 pages, 5 figures. Supplementary Information 7 pages, 9 figures
09/2010;
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[show abstract]
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ABSTRACT: The LaAlO3/SrTiO3 interface provides a unique platform for controlling the
electronic properties of the superconducting semiconductor SrTiO3. Prior
investigations have shown that two-dimensional superconductivity can be
produced at the LaAlO3/SrTiO3 interface and tuned electrostatically. The
recently demonstrated reversible control of the metal-insulator transition at
the same interface using conductive atomic force microscopy (c-AFM) raises the
question of whether this room-temperature technique can produce structures that
exhibit superconducting, normal metallic and insulating phases at sub-Kelvin
temperatures. Here we report low-temperature magnetotransport experiments on
conducting structures defined at an otherwise insulating LaAlO3/SrTiO3
interface. A quantum phase transition associated with the formation of Cooper
pairs is observed in these predefined structures at sub-Kelvin temperatures.
However, a finite resistance remains even at the lowest temperature. At higher
magnetic fields, interfaces with high mobility also exhibit strong Shubnikov-de
Haas oscillations as well as a larger Ginsburg-Landau coherence length. Cooper
pair localization, spin-orbit coupling, and finite-size effects may factor into
an explanation for some of the unusual properties observed.
09/2010;
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Advanced Materials 02/2010; 22(6):759-62. · 13.88 Impact Factor
