Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session B37a: Complex Oxide Interfaces and Heterostructures - Ruthenates, LaAlO3/SrTiO3Focus
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Sponsoring Units: DMP DCMP Chair: Ryan Comes, Auburn University Room: 383 |
Monday, March 13, 2017 11:15AM - 11:51AM |
B37a.00001: Controlling Electronic Band Structure and Correlations by Dimensional Confinement and Epitaxial Strain in Complex Oxide Thin Films Invited Speaker: Kyle Shen Our ability to control the electronic structure of materials, for instance at semiconductor interfaces, has had enormous scientific and technological implications. Recently, this concept has been extended to materials which possess inherently strong quantum many-body interactions which can harbor novel electronic or magnetic properties. Here, we demonstrate the ability to control the band structure and effective strength of correlations through dimensional confinement or epitaxial strain in complex oxide thin films. We employ epitaxial strain to drive a Lifshitz transition in thin films of Sr$_2$RuO$_4$, and also utilize dimensional confinement to achieve large mass enhancements over the bulk in atomically thin iridate thin films (IrO$_2$). We also use dimensional confinement and epitaxial strain to drive metal-insulator transitions and modify the magnetic ground states in atomically thin films of perovskite ruthenates (BaRuO$_3$ and Ca$_2$RuO$_4$). [Preview Abstract] |
Monday, March 13, 2017 11:51AM - 12:03PM |
B37a.00002: Controlling the electronic ground state of Ca2RuO4 thin films with epitaxial strain Jacob Ruf, Hari Nair, Yang Liu, Darrell Schlom, Kyle Shen Rapid progress in thin-film synthesis techniques in recent years has enabled unprecedented control over the crystal structure of thin films of correlated quantum materials, via knobs such as epitaxial strain and dimensionality. In favorable circumstances where there is strong coupling between a material's crystal structure and its electronic properties, subtle changes to the former can be used to tune dramatic changes in the latter. Here we employ this general approach to the prototypical layered ruthenate Ca$_{2}$RuO$_{4}$, showing that the multi-orbital Mott insulating ground state of bulk Ca$_{2}$RuO$_{4}$ can be suppressed (enhanced) in thin films under biaxial compressive (tensile) strain, grown by molecular-beam epitaxy on LaAlO$_{3}$ and NdAlO$_{3}$ (NdGaO$_{3}$) substrates, respectively. Using a combination of x-ray and electron diffraction together with photoemission spectroscopy and electrical transport measurements, we probe how strain modifies the atomic structure of these strained Ca$_{2}$RuO$_{4}$ films and elucidate how these modifications redistribute the low-energy spectral weight near the Fermi level. Concomitant strain-dependent changes to the magnetic ordering instabilities in these systems will also be discussed. [Preview Abstract] |
Monday, March 13, 2017 12:03PM - 12:15PM |
B37a.00003: Strain and the Metal Insulator Transition in bulk and thin film Ca$_2$RuO$_4$ Qiang Han, Andrew Millis The experiments done by J.P.Ruf et.al show that the multi-orbital Mott insulating ground state of bulk Ca2RuO4 can be suppressed (enhanced) in thin films under biaxial compressive (tensile) strain. In this paper, DFT+DMFT, DFT+U methods are used to study the strain dependence of the metal insulator phase transition in bulk and thin-film Ca$_2$RuO$_4$. The interplay between bulk strain, substrate pinning of in-plane lattice constants, octahedral distortions and the metal-insulator transition leads to a strain contribution to the energetics of the first order metal-insulator transition which is substantially amplified in films relative to bulk. Comparison to recent data is presented, and generalization of the theory to other transition metal oxides is discussed. [Preview Abstract] |
Monday, March 13, 2017 12:15PM - 12:27PM |
B37a.00004: Temperature-dependence of hypersound dynamics in SrTiO$_{\mathrm{3}}$/SrRuO$_{\mathrm{3}}$ heterostructures studied by ultrafast spectroscopy Chi-Yuan Yang, Ajay K Yadav, Ramamoorthy Ramesh, Yu-Chieh Wen, Chia-Hao Hsu, Maw-Kuen Wu, Chih-Ta Chia, Kung-Hsuan Lin Strontium titanate (SrTiO$_{\mathrm{3}}$, STO) and strontium ruthenate (SrRuO$_{\mathrm{3}}$, SRO) are complex oxide with perovskite structure. Their property, such as thermoelectricity and superconductivity, has been widely investigated for scientific and industrial purposes. Recently, complex oxide heterostructures can be grown by pulsed laser deposition. It opens many possibilities f or new properties of materials. With ultrafast pump-probe spectroscopy, we demonstrated that metal-like SRO thin film can be served as a phonon transducer to generate hypersound with frequency of several tens to several hundreads of GHz. This technique can be utilized to study not only the elastic properties of perovskite thin films but also the interfaces. In this study, we used this technique to study the temperature dependence of structural phases in STO. During the crossing over the soft-mode transition in STO around 110 K, the shortening of phonon lifetime were also observed. [Preview Abstract] |
Monday, March 13, 2017 12:27PM - 12:39PM |
B37a.00005: Intermediate surface structure between step bunching and step flow in SrRuO$_{3}$ thin film growth Giulia Bertino, Anna Gura, Matthew Dawber We performed a systematic study of SrRuO$_{3}$ thin films grown on TiO$_{2}$ terminated SrTiO$_{3}$ substrates using off-axis magnetron sputtering. We investigated the step bunching formation and the evolution of the SRO film morphology by varying the step size of the substrate, the growth temperature and the film thickness. The thin films were characterized using Atomic Force Microscopy and X-Ray Diffraction. We identified single and multiple step bunching and step flow growth regimes as a function of the growth parameters. Also, we clearly observe a stronger influence of the step size of the substrate on the evolution of the SRO film surface with respect to the other growth parameters. Remarkably, we observe the formation of a smooth, regular and uniform ``fish skin'' structure at the transition between one regime and another. We believe that the fish skin structure results from the merging of 2D flat islands predicted by previous models. The direct observation of this transition structure allows us to better understand how and when step bunching develops in the growth of SrRuO$_{3}$ thin films. [Preview Abstract] |
Monday, March 13, 2017 12:39PM - 12:51PM |
B37a.00006: Ferromagnetism and conductivity in atomically thin SrRuO3 Hans Boschker, Cameron Hughes, Takayuki Harada, Tomoya Asaba, Ray Ashoori, Alexander Boris, Hans Hilgenkamp, Megan Holtz, Lu Li, Jochen Mannhart, David Muller, Xiao Renshaw Wang, Darrell Schlom, Arsen Soukiassian Atomically thin ferromagnetic and conducting electron systems combine the advantages of two-dimensional electron systems with those of magnetic materials, i.e., state control by electric and magnetic fields is expected to be possible. Most magnetic and conducting transition metal oxide materials, however, lose their functional properties well before the single-unit-cell layer thickness is reached; typically a non-conducting and non-magnetic dead-layer is present. SrRuO3 has been proposed to be a half-metal if a single unit-cell-thick layer is embedded in a SrTiO3 matrix [1]. Here we present (SrRuO3)1--(SrTiO3)5 superlattices of exceptional quality [2]. In these superlattices the electron system comprises only a single RuO2 plane. We observe conductivity down to 50 mK, a ferromagnetic state with a Curie temperature of at least 30 K, and signals of magnetism persisting up to \textasciitilde 100 K. [1] Verissimo-Alves, M., Garc\'{\i}a-Fern\'{a}ndez, P., Bilc, D.I., Ghosez, P. {\&} Junquera, J., Phys. Rev. Lett. 108, 107003 (2012). [2] Hughes, C.R., et al., arXiv:1609.08901 (2016). [Preview Abstract] |
Monday, March 13, 2017 12:51PM - 1:03PM |
B37a.00007: Understanding the A-Cation Order Dependent Band Gap Variation in Ruddlesden-Popper Oxides Yongjin Shin, James Rondinelli Many atomically layered oxide superlattice are constructed from three-dimensionally connected bulk perovskites. Here we examine the electronic structure of quasi-two-dimensional Ruddlesden-Popper (RP) oxides, focusing on (LaSr)AlO$_{4}$ and changes induced by A cation order. The partial connectivity of perovskite layers enables the structure to distort without tilting or further symmetry reduction. It also provides opportunities to tune the Coulomb interactions between adjacent atomic AO layers that produce internal electric fields. Indeed, an aluminate RP superlattice was recently predicted to show massive band gap variations, up to 200$\%$, depending on the A cation ordering using first-principles electronic structure calculations. Here we extend this concept to a greater number cation ordered variants, showing that longer period arrangements of the monoxide planes lead to greater control over the band gap and even its full collapse, i.e., metal-insulator transition, using density functional theory calculations. We conclude by summarizing our findings into a set of working principles for band gap control in layered oxides without chemical doping or changes in cation stoichiometry. [Preview Abstract] |
Monday, March 13, 2017 1:03PM - 1:15PM |
B37a.00008: Evolution of subband structure with gate-tuning at LaAlO3/SrTiO3 interfaces Lucas Tang, Sander Smink, Linde van Heeringen, Jaap Geessinck, Abimanuya Rana, Ankur Rastogi, Jan Kees Maan, Alexander Brinkman, Uli Zeitler, Hans Hilgenkamp, Alix McCollam The outstanding characteristic of LaAlO3/SrTiO3 heterostructures is the formation of a high mobility 2D electron gas (2DEG) at the interface. The additional presence of superconductivity, magnetism and large spin-orbit coupling in these systems suggests that strong correlations play an important role in the electronic properties, in contrast to conventional semiconductor-based 2DEGs. Knowledge of the electronic bandstructure, and the interdependence of conduction electron density and properties is therefore essential for our understanding of these materials. We present new results of low temperature transport measurements in a high mobility LaAlO3/SrTiO3-based heterostructure, in magnetic fields up to 33 T. Shubnikov de-Haas oscillations are observed, revealing several subbands with different carrier densities. By application of an electric field in the back gate geometry, the Fermi level is tuned and thus we are able to map the smooth evolution of the subbands and their properties with carrier density. These results are in good agreement with recent theoretical work, such that we can disentangle the complex band structure, and quantify aspects such as Rashba spin-splitting and the mixing of orbital character. [Preview Abstract] |
Monday, March 13, 2017 1:15PM - 1:27PM |
B37a.00009: Full electrostatic control of the band structure of the LaAlO$_{3}$-SrTiO$_{3}$ interface two-dimensional electron system Sander Smink, Jorrit de Boer, Martin Stehno, Alexander Brinkman, Wilfred van der Wiel, Hans Hilgenkamp The two-dimensional electron system at the interface between LaAlO$_{3}$ and SrTiO$_{3}$ has several unique properties that can be tuned by an externally applied gate voltage. Our magnetotransport data on top-gated Hall bars reveals a $d_{yz,xz}$ Lifshitz transition at a carrier density of 2.9 x 10$^{13}$ cm$^{-2}$ and a surprising reduction of $d_{xy}$-type carrier density with gate voltage above this transition. These observations indicate a gate-tunable band structure, which is controlled by the electrostatic confinement. This is supported by self-consistent Schr\"{o}dinger-Poisson calculations, which reproduce the observed reduction of $d_{xy}$-type charge carrier density by including interband electronic correlations. In combination with back-gating, we show that the top-gated $d_{yz,xz}$ Lifshitz transition can be tuned by a back-gate voltage, establishing full electrostatic control of the band structure and confinement of the system. The expected effect of either a top- or back-gate voltage on the boundary conditions of the Schr\"{o}dinger-Poisson model is confirmed by the experimental results. [Preview Abstract] |
Monday, March 13, 2017 1:27PM - 1:39PM |
B37a.00010: High Mobility Electron Systems at Multipolar Oxide Interfaces Giordano Mattoni, Alessio Filippetti, Nicola Manca, Nils Verhagen, Pavlo Zubko, Andrea D. Caviglia Polar interfaces in complex oxides heterostructures constitute a unique playground for 2D electron systems (2DES), where exotic properties such as superconductivity and magnetism can arise from combinations of bulk insulators. Structural compatibility of these materials allows to build heterostructures where different polar fields can interact to induce novel electronic states. In this work, we investigate the metallic state arising in the SrTiO$_3$/LaAlO$_3$/WO$_3$ multipolar interface. Our measurements uncover a thickness-dependent transition from an insulating to a metallic state with electron mobilities up to 80,000 cm$^2$/Vs. Low-temperature magnetotransport reveals a strong magnetoresistance reaching 1000\% at 10T and 1.5K, accompanied by non-linear Hall effect and quantum oscillations of conductance. Our results show how interfaces with multipolar character allow large flexibility in the design of the confinement potential, opening new possibilities for 2DES in strongly correlated materials. [Preview Abstract] |
Monday, March 13, 2017 1:39PM - 1:51PM |
B37a.00011: Quantum Confinement at Polar Oxide Interfaces Stefano Gariglio, Danfeng Li, Zhenping Wu, Wei Liu, Alexandre Fete, Margherita Boselli, Sebastien Lemal, Nicholas Bristowe, Philippe Ghosez, Marc Gabay, Jean-Marc Triscone The discovery of a two-dimensional electron liquid (2DEL), confined at the interface between the two band insulators LaAlO$_3$ (LAO) and SrTiO$_3$ (STO) has generated tremendous research interest. The 2DEL confinement lifts the degeneracy of Ti $t_{2g}$ orbitals and promotes exotic physical properties. A previous study [1] has demonstrated that a 2DEL is also observed when LAO is alloyed with STO (La,Al)$_{1-x}$(Sr,Ti)$_x$O$_3$ (LASTO:$x$). The threshold thickness required for the onset of conductivity scales with $x$. We present here a study of superconductivity at the (LASTO:0.5)/STO interface. The thickness of the 2DEL, measured using perpendicular and parallel critical fields, is larger than the one at the LAO/STO interface. This change is due to a modification on the confining potential linked to a reduced charge transfer that is scaling as $1/x$. This scenario is also confirmed by a self-consistent Poisson-Schrödinger model and ab initio calculations. These compelling evidences support an intrinsic origin to the formation of the 2DEL in the LAO/STO system. \\ [1] M.L. Reinle-Schmitt, et al., Nature Commun. 3, 932 (2012). [Preview Abstract] |
Monday, March 13, 2017 1:51PM - 2:03PM |
B37a.00012: Photoinduced Nanodomain Pattern Transformation in Ferroelectric/Dielectric Superlattice Heterostructure Youngjun Ahn, Joonkyu Park, Anastasios Pateras, Matthew Rich, Qingteng Zhang, Pice Chen, Mohammed Yusuf, Haidan Wen, Matthew Dawber, Paul Evans Ultrathin ferroelectric layers in oxide heterostructures can spontaneously form domains with alternating polarization and nanometer-scale periodicity. The formation of the domain pattern is driven by the depolarization field arising from the interfacial discontinuity of the polarization. The mechanism of tuning and screening of the depolarization field and its correlation with the domain morphology is crucial to the physics of nanodomains. We show that a series of above-bandgap optical pulses induce a transformation of the domain pattern to a uniform polarization configuration. The transformation is observed via synchrotron hard x-ray scattering, in which there is a decrease in the intensity of domain diffuse scattering accompanied by a lattice expansion of 0.6{\%}. The threshold optical fluence for the transformation is 1.8 mJ/cm$^{\mathrm{2}}$ per pulse at a repetition rate of 54 kHz. A thermodynamic model based on Landau-Ginzburg-Devonshire theory shows that the domain transformation and lattice expansion along surface normal can be induced by screening the depolarization field. Above a critical value of the screening parameter in this model the uniform polarization configuration is energetically favored. [Preview Abstract] |
Monday, March 13, 2017 2:03PM - 2:15PM |
B37a.00013: Enhancement of electrical transport modulation in epitaxial VO2 nanowire field-effect transistor Hidekazu Tanaka, Masashi Chikanari, Teruo kanki Strongly correlated system vanadium dioxide VO2 has attracted widespread concerns from researchers as an exciting electronic material, due to the many intriguing features, especially metal-insulator transition (MIT) in vicinity of room temperature. In this work, we report a diverse geometry for high sensitivity in the transport modulation. By taking advantage of nanometer scale channel, instead of thin film channels, we demonstrated the enhancement of resistance modulation by applying gate voltage. Also we designed the insulating gate, consisting of high-k material Ta2O5/organic polymer parylene-C hybrid insulator. Such as this hybrid gate dielectric would effectively reduce interface deterioration of active channel oxide and provide sufficient carrier density. Moreover, benefited from the nanometer scale channel, the VO2 nanowire-based transistor could deliver a resistance modulation ratio over 8.5{\%}, which are about 10 folds higher than that of the film case. Furthermore, this result is explained that in spite of the stronger field distribution in the edge parts of VO2 nanowire channel yielded little carrier density, the generated mobility modulation would biquadratic increase according to Brinkman-Rice picture as new finding. [Preview Abstract] |
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