Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E45: Complex Oxide Surfaces, Interfaces, and Thin Films IFocus
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Sponsoring Units: DCMP Chair: David Lederman, UC Santa Cruz Room: BCEC 211 |
Tuesday, March 5, 2019 8:00AM - 8:12AM |
E45.00001: Mechanical strain-tuned magnetism and AFM Neel temperature by 90 K in PrVO3 thin films Wilfrid Prellier The transition-metal oxides with ABO3 type perovskite structure show a strong coupling between spin-orbital and lattice degrees of freedom. Here, we present an experimental study of magnetic response to the residual strain in PVO thin films by growing PVO films on a variety of single crystal substrates and by varying PVO film thickness on a single crystal substrate. PrVO3 in bulk, being a strong anti-ferromagnet shows TN~ 130 K [1]. Our study reveals that the lattice distortion via misfit strain pave the way towards tuning the anti-ferromagnetic ordering temperature in PrVO3 thin films, resulting in a non-trivial evolution of the Neel temperature (TN) with substrate pseudo-cubic lattice parameter and PVO film thickness. We demonstrate that the strain produced via mechanical strain engineering, tune TN of PVO films in the range of 90 K. Moreover, we also show that PVO thin films show low temperature ferromagnetic behavior along with the insulating properties irrespective of the substrate. |
Tuesday, March 5, 2019 8:12AM - 8:24AM |
E45.00002: Unusual Electronic Phase Separation Phenomena in Manganite Ultrathin Films Hongyan Chen, Yang Yu, Bai Yu, Hanxuan Lin, xiaolong Li, Hao Liu, Tian Miao, Yunfang Kou, Yongsheng Zhang, Yan li, Jin Tang, Zechao Wang, Peng Cai, Yinyan Zhu, Zhe Wang, Zhaohua Cheng, Xiaoyan Zhong, Wenbin Wang, Xingyu Gao, Ruqian Wu, Lifeng Yin, Jian Shen Ultrathin films often exhibit two-dimensional characteristics that are distinctly different from their bulk counterpart. In this work, we show an unusual behavior in La0.7Sr0.3MnO3 (LSMO) ultrathin films grown on SrTiO3 (001) (STO) substrate. Combining scanning tunneling microscopy and magneto-optical Kerr effect measurements, we have obtained the evolution of the magnetic state of the LSMO ultrathin films as a function of thickness. Strikingly, the LSMO ultrathin films are electronically phase separated in both lateral and vertical directions in thickness range between 4 and 7 unit cells. Specifically, the films are formed by 3 unit cell thick antiferromagnetic base layers, on top of which the layers consist of ferromagnetic metallic nanodisks in antiferromagnetic matrix. At 8 unit cells, an abrupt shear strain relief occurs by forming twinning patterns along [010] and [100] directions. After the shear strain is relieved, the whole films transform into a uniform ferromagnetic metallic state. Our observation reveals the richness of electronic and magnetic phases for strongly correlated systems even in their two-dimensional limit. |
Tuesday, March 5, 2019 8:24AM - 8:36AM |
E45.00003: 2DEG state at LaInO3/BaSnO3 interface Young Mo Kim, Youjung Kim, Juyeon Shin, Kookrin Char In order to identify the origin of the large conductance enhancement in the polar interface of LaInO3/BaSnO3, we studied the variation of the conductance enhancement in LaIn1-xGaxO3/BaSnO3 interface. We found that the magnitude of the conductance enhancement decreased as Ga ratio increased and eventually completely disappeared in the case of LaGaO3/BaSnO3. The conductance of the interface, when present, reached its maximum values when LaIn1-xGaxO3 was about 4 unit cell thick, beyond which the conductance started to decrease slowly. Based on such findings, we developed a model for interface polarization in LIO, in which the polarization exists only in the 4 unit cell thick LIO near the interface. Such a model, when aided by 1D Poisson-Schrödinger equation, produces the n2D consistent with the experimental results. In addition, by introducing a deep donor density in LIO, we are able to fit the slow relaxation of the interface conductance. Our complete model, comprised of interface polarization in the 4 unit cell thick LIO and the resulting 2DEG state in BSO with 2 nm confinement length, also explains in a consistent way the entire experimental data of the recent doping dependence of the LIO/BLSO interface conductance on both SrTiO3 and MgO substrates. |
Tuesday, March 5, 2019 8:36AM - 8:48AM |
E45.00004: Tuning the physical properties via Sr doping in the 4d transition metal oxide LaRhO3 Juan Jiang, Sangjae Lee, Frederick J Walker, Charles H Ahn Perovskite transition metal oxides exhibit various novel properties due to the interactions of strongly correlated electrons. We discuss the physical properties of Rhodate thin film in this talk. We grow high quality La1-xSrxRhO3 thin films (up to x=0.5) on LaAlO3 substrates by molecular beam epitaxy, and characterize their electrical and magnetic properties. Electrical anomalies and ferromagnetic signatures are observed. Strain effects are discussed, which might play a role in determine the physical properties of our thin films. |
Tuesday, March 5, 2019 8:48AM - 9:00AM |
E45.00005: Modulation of manganite thin-film properties by strontium titanate excitons Chi Sin Tang, Xinmao Yin, Le Wang, Andrew Thye Shen Wee, Junling Wang, Andrivo Rusydi A comprehensive investigation of the optical, electronic and magnetic properties of La0.7Sr0.3MnO3 films on SrTiO3 (LSMO/STO) and other substrates is conducted using multiple experimental techniques. There is a significant difference in the optical properties of LSMO/STO even in the case of 87.2nm-thick LSMO/STO as compared to those of LSMO on other substrates. We observed interesting excitonic features in the LSMO/STO thin-film at ~4eV. This could be due to formation of anomalous charged excitonic complexes. Based on spectral-weight transfer analysis, anomalous excitonic effects from STO strengthen the electronic-correlation in LSMO films. This results in optical spectral changes related to intrinsic Mott-Hubbard properties in the manganite films. While lattice strain influences the optical properties of the LSMO thin-films, strong e-e and e-h interactions from the substrate play a significant role as well. |
Tuesday, March 5, 2019 9:00AM - 9:12AM |
E45.00006: Thickness-dependent metal-to-insulator transition in La-doped SrTiO3 thin films Yeongjae Shin, Claudia Lau, Sangjae Lee, Frederick J Walker, Charles H Ahn The electronic and structural properties of La-doped SrTiO3 (LSTO) films grown by molecular beam epitaxy are studied as a function of film thickness and La doping. We demonstrate that electronic transport is highly affected by the insulating dead layers inside LSTO films, whose thickness depends on La doping. As the film thickness is reduced below the dead layer thickness, an abrupt metal-to-insulator transition occurs. We attribute the existence of insulating layers to the surface structure of LSTO. The reduced conductivity of LSTO films due to dead layers can be counteracted by growing additional capping layers on top of the LSTO surface, indicating the strong relationship between insulating dead layers and surface structure of LSTO films. Synchrotron-based X-ray scattering analysis is used to test this hypothesis. Our results emphasize the importance of surface structure studies for functional oxides in the thin film limit and provide a guiding principle to fabricate oxide nanoscale devices. |
Tuesday, March 5, 2019 9:12AM - 9:24AM |
E45.00007: Thickness-dependent oxygen octahedral distortions in perovskite thin films as an adaption to the heterointerface Jennifer Fowlie, Céline Lichtensteiger, Marta Gibert, Hugo Meley, Philip Willmott, Jean-Marc Triscone Distortions of the oxygen octahedral network of ABO3-type perovskites are one of the most common features that develop in oxide heterostructures as a response to the epitaxial strain imposed by the substrate. This behaviour, which can be characterised as rigid tilts and rotations of the octahedra themselves, is readily studied quantitatively by synchrotron x-ray diffraction at half-integer Bragg positions [1]. |
Tuesday, March 5, 2019 9:24AM - 9:36AM |
E45.00008: The spin texture in a SrTiO3(111) two-dimensional electron gas Pan He, Siobhan McKeown Walker, Shulei Zhang, F. Y. Bruno, M. S. Bahramy, Jongmin Lee, Rajagopalan Ramaswamy, Kaiming Cai, Olle Heinonen, Giovanni Vignale, Felix Baumberger, Hyunsoo Yang We report the observation of a bilinear magnetoelectric resistance (BMER) signal in the d-orbital two-dimensional electron gas (2DEG) at the SrTiO3 (STO) (111) surface, demonstrating a spin-splitting. We show that our BMER measurements reveal a three-fold symmetric out-of-plane spin component that breaks the six-fold symmetry of the 2DEG subband dispersion, and an in-plane spin component locked perpendicularly to the momentum. By performing tight-binding supercell calculations based on the relativistic density functional theory of the STO bulk band structure, we find that this 3D spin texture is fully described by the effects of confinement of the STO t2g conduction band in the (111) plane. We also show that the BMER can be substantially tuned through oxygen vacancy doping, electrostatic gating and temperature variation. Our findings highlight the untapped potential of SrTiO3 (111) based 2DEGs as a playground for spintronic applications. |
Tuesday, March 5, 2019 9:36AM - 9:48AM |
E45.00009: WITHDRAWN ABSTRACT
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Tuesday, March 5, 2019 9:48AM - 10:00AM |
E45.00010: Anomalous behaviour of phonon modes – Magnetic properties correlations in La0.7Sr0.3MnO3/SrRuO3 superlattices Roshna S H, P Padhan, Wilfrid Prellier Artificial superstructure of (111) oriented La0.7Sr0.3MnO3 (LSMO)/SrRuO3 (SRO) were grown on (111) oriented SrTiO3 substrate using pulsed laser deposition.Microstructure quality and coherency of interafaces were studied using high resolution transmission electron microscopy .The growth epitaxy, crystalline quality,crystal structure and artificial bilayer periodicity of these superlattices were studied using x-ray diffraction. The cumulative strain in these superlattices was studied from the reciprocal space mapping (RSM) .The RSM image of these superlattices indicates relaxation in some crystallographic directions.The magnetic exchange coupling at the interfaces of the LSMO-SRO has been investigated with the in-plane and the out-of-plane oriented magnetic field. The phonon mode anomaly of these superlattices were observed in the temperature dependent frequencies of the Raman lines. The observed peak at around 160 K and step like anomaly at around 350 K of the Raman peak frequencies provide strong evidence of magnetic phase transition of SRO and LSMO respectively. The observed anomalies in phonon modes in Raman scattering are discussed in terms of spin phonon coupling and delocalization of polaronic states in the vicinity of magnetic phase transition temperature of LSMO and SRO. |
Tuesday, March 5, 2019 10:00AM - 10:12AM |
E45.00011: Induced ferromagnetism due to oxygen vacancies at the YBa2Cu3O7/SrTiO3 Interface Kyro Boom, Mi He, Ee Min Chia, Jian-Xin Zhu, Jason Haraldsen Complex oxide heterostructures provide a large playground of order parameters that can introduce a wide range of emergent phenomena. In the study, we set out to explain the emergent magnetic properties at the interface between YBa2Cu3O7/SrTiO3. Using density functional theory, we determined the electronic and magnetic properties for a simulated heterostructure with and without oxygen vacancies. It is shown that the sheer presence of the interface is not enough to produce a magnetic response. However, with the introduction of oxygen vacancies, we show that there is a shifting of the d orbital electron energies on the transition-metal atoms that induces a magnetic moment at the interface. This work details the effects of oxygen vacancies on complex oxide heterostructures, which has the ability to provide critical insight into future applications of oxide electronics. |
Tuesday, March 5, 2019 10:12AM - 10:24AM |
E45.00012: Mechanism of the irreversible back gate doping at the LaAlO3/SrTiO3 Interface Chunhai Yin, Sander Smink, Inge Leermakers, Lucas Tang, Nikita Lebedev, Uli Zeitler, Hans Hilgenkamp, Jan Aarts The two-dimensional electron gas (2DEG) formed at the LaAlO3/SrTiO3 (LAO/STO) interface exhibits rich physical properties such as superconductivity and magnetism. Additionally, due to the large dielectric constant of STO, the 2DEG can be controlled by a back gate voltage (VG). When applying VG to the system, a commonly observed phenomenon is that the sheet resistance follows an irreversible route when VG is swept first forward and then backward. The explanation as given by Biscaras et al. [1] is that the Fermi energy is close to the top of the quantum well (QW) and high mobility electrons escape the QW and get trapped in STO when the carrier density goes beyond a critical value. |
Tuesday, March 5, 2019 10:24AM - 10:36AM |
E45.00013: Influence of defects on surface morphology and electronic structure in BiVO4 Wennie Wang, Mingzhao Liu, Kyoung-Shin Choi, Giulia Galli Bismuth vanadate (BiVO4) has several electronic properties that make it a promising candidate as a photoanode for water photocatalysis; these include strong absorption across much of the visible spectrum and a conduction band edge near the hydrogen evolution potential. However, charge transport and interfacial charge transfer have been reported to be limiting factors for PEC performance. Understanding the connections between surface morphology and PEC performance remains in its nascent stages, and building an accurate structural model is key. Here, we use density functional theory calculations to study the surface morphology and electronic structure of BiVO4, and compare them with experiment. We investigate pristine surfaces and compare with those that have defects, and discuss the implications on PEC performance. |
Tuesday, March 5, 2019 10:36AM - 10:48AM |
E45.00014: Electronic Symmetry of La0.67Sr0.33MnO3/SrTiO3 Interfaces as a Function of Film Thickness Joel E Taylor, Kun Zhao, Mohammad Saghayezhian, Jiandi Zhang, Louis H Haber, E Ward Plummer Second harmonic generation (SHG) is a well known optical technique for probing electronic symmetry originating from regions of broken symmetries. For La0.67Sr0.33MnO3/SrTiO3 (LSMO/STO) buried interfaces, rotational anisotropic SHG is capable of characterizing interfacial electronic symmetry. Using film thickness and growth conditions to control the interface structure for LSMO/STO buried interfaces, induced changes in the electronic symmetry are detected with rotational anisotropic SHG. Data accumulated for LSMO/STO demonstrates thickness-dependent enhanced four-fold electronic symmetry patterns which are contrary to the measured C4v electronic symmetry measured using atomically resolved electron microscopy and spectroscopy. Furthermore, the relative angles of the peak intensities between in-plane and out-of-plane polarization geometries varies with film thickness. Rotational anisotropy SHG of LSMO/STO thin films will be presented from <5 unit cell to 300+ unit cell LSMO/STO heterostructures. |
Tuesday, March 5, 2019 10:48AM - 11:00AM |
E45.00015: Decoupling carrier concentration and electron-phonon coupling in oxide heterostructures Derek Meyers, Ken Nakatsukasa, Sai Mu, Lin Hao, Junyi Yang, Yue Cao, Gilberto F L Fabbris, Hu Miao, Jonathan Pelliciari, Daniel McNally, Marcus Dantz, Eugenio Paris, Evguenia Karapetrova, Yongseong Choi, Daniel Haskel, Padraic Shafer, Elke Arenholz, Schmitt Thorsten, Tom Berlijn, Steven Johnston, Jian Liu, Mark Dean We present the results of resonant inelastic x-ray scattering at the O K-edge on superlattices of form nSrIrO3/mSrTiO3. Multiple phonon satellite peaks are observed corresponding to the 4th longitundal optical mode of SrTiO3 allowing direct extraction of the electron-phonon coupling strength. As the values of n and m are varied a systematic change in the relative intensity of the satellite features is observed indicating large changes to the electron-phonon coupling strength. In the absence of signifcant carrier doping this result shows the heterostructure morphology is able to independently tune this important interaction. Theoretical calculations indicate the Fröhlich mechanism dominates the electron-phonon coupling in these superlattices, with the reduced polarity and increased ε∞ driving the observed changes in the electron-phonon coupling. |
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