Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session R09: Electronic Structure, Topological Effects and Magnetotransport in Complex Oxide SystemsFocus
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Sponsoring Units: DMP GMAG Chair: Jason Hoffman, Harvard University Room: LACC 301A |
Thursday, March 8, 2018 8:00AM - 8:12AM |
R09.00001: Electronic Structure of LaNiO3 Thin Films and (111)-Oriented LaNiO3/LaMnO3 Heterostructures Probed by ARPES Flavio Bruno, Siobhan McKeown Walker, W. Tromp, Marta Gibert, O. Peil, Alberto De la Torre, S. Ricco, Z. Wang, Sara Catalano, Anna Tamai, F. Bisti, V. Strocov, Jean-Marc Triscone, Felix Baumberger We report measurements of the electronic structure of (111)-oriented [LaNiO3/LaMnO3] superlattices and LaNiO3 epitaxial thin films both (111) and (001) oriented by means of angle resolved photoemission spectroscopy (ARPES). For thin films we observe a 3D Fermi surface with an electron pocket at the Brillouin zone center and hole pockets at the zone vertices. Taking advantage of the large electron escape depth of soft x-ray ARPES we measure the Fermi surface of buried nickelate layers in superlattices. Heterostructures with thick LaNiO3 layers are metallic and present a similar electronic structure to thin films. However, as the thickness of the LaNiO3 is reduced to 7 monolayers the superlattices become insulating. These heterostructures do not show a marked redistribution of spectral weight in momentum space but exhibit a pseudogap of ≈ 50 meV. APL Materials 5, 016101 (2017). |
Thursday, March 8, 2018 8:12AM - 8:24AM |
R09.00002: Magnetotransport Studies of BaPbO3/BaBiO3 Bilayer Thin Films Nicholas Breznay, Adam Shaw, Gerwin Hassink, Robert Hammond, Malcolm Beasley Barium lead bismuth oxide (BaPb1-xBixO3) shows a complex phase diagram with adjacent superconducting, insulating, and charge ordered states. The effects of disorder and stripe-like structural phase separation have recently been studied in bulk single crystals [P. Giraldo-Gallo et al. Nat. Comms. 6, 8231 (2015)]; here we study the effects of disorder in a model system - BaPbO3/BaBiO3 bilayer thin films. Low temperature magnetotransport measurements show a crossover between weak localization and antilocalization near the superconducting transition, and we extract the associated electronic dephasing and spin-orbital lifetimes. |
Thursday, March 8, 2018 8:24AM - 8:36AM |
R09.00003: Large positive linear magnetoresistance in the two-dimensional t2g electron gas at the EuO/SrTiO3 interface Alexander Demkov, Kristy Kormondy, Lingyuan Gao, Xiang Li, Sirong Lu, Agham Posadas, Shida Shen, Maxim Tsoi, Martha McCartney, David Smith, Jianshi Zhou, Leonid Lev, V. Strocov The development of novel nano-oxide spintronic devices would benefit greatly from interfacing with emergent phenomena at oxide interfaces. In this paper, we integrate highly spin-split ferromagnetic semiconductor EuO onto perovskite SrTiO3 (001). A careful deposition of Eu metal by molecular beam epitaxy results in EuO growth via oxygen out-diffusion from SrTiO3. This in turn leaves behind a highly conductive interfacial layer through generation of oxygen vacancies. Below the Curie temperature of 70 K of EuO this spin-polarized two-dimensional t2g electron gas at the EuO/SrTiO3 interface displays very large positive linear magnetoresistance (MR). Soft-x-ray angle-resolved photoemission spectroscopy (SX-ARPES) shows the t2g nature of the carriers. First principles calculations strongly suggest the Zeeman splitting, caused by proximity magnetism of oxygen vacancies in SrTiO3, is responsible for the MR. This system offers an as-yet-unexplored route to pursue proximity-induced effects in the oxide two-dimensional t2g electron gas. |
Thursday, March 8, 2018 8:36AM - 9:12AM |
R09.00004: Theory of topologically induced properties of surfaces and interfaces Invited Speaker: David Vanderbilt I will discuss several examples of systems in which the bulk topology of the material plays a central role in determining the properties of surfaces or interfaces. First I will review our recent proposal for topological switching in antiferroelectrics [1], in which we computationally identified materials that are predicted to be in a topological insulator (TI) phase in the polar state, but topologically trivial in the antipolar state. This raises the possibility of electric-field induced switching between TI and non-TI behavior, although there is a potential question whether such switching is really possible in view of the topologically protected metallic states that should exist at antipolar-polar domain walls. Second, I will describe our work in which we construct simple tight-binding models of axion insulators, in which the topological index is protected by inversion rather than TR symmetry. I will discuss the conditions under which a half-integer quantized anomalous Hall conductivity should be present at the surface, and how the surface termination determines its sign. If time permits, I will also discuss the bulk-boundary correspondence for topological crystalline insulators and its consequences for surface and interface properties of such materials. |
(Author Not Attending)
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R09.00005: Magnetotransport in nanowires realised at the LaAlO3/SrTiO3 interface Margherita Boselli, Adrien Waelchli, Ritsuko Eguchi, Stefano Gariglio, Jean-Marc Triscone
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Thursday, March 8, 2018 9:24AM - 9:36AM |
R09.00006: Superconductivity in NdxSr1-xTiO3 Films Grown using Hybrid Molecular Beam Epitaxy Yilikal Ayino, Jin Yue, Xinxin Cai, Tianqi Wang, Laxman Thoutam, Bharat Jalan, Vlad Pribiag We present experimental results showing superconductivity in NdxSr1-xTiO3 thin films (50-250 nm) grown using hybrid MBE approach, where Nd3+ is expected to carry net magnetic moment. We measure anisotropic resistance along the two orthogonal in-plane channels. In the high resistance direction we observe a smooth transition from metallic to superconducting state at a critical temperature (Tc ~ 0.2K). However, along the low resistance channel the resistance rises by up to an order of magnitude near Tc before turning superconducting. We discuss these results in the context of anisotropic in-plane Josephson coupling. Furthermore, the out of plane upper critical field (Hc2) as a function of temperature shows opposite curvature from what is expected based on Wethamer-Helfand-Hohenberg theory, and does not saturate down to ~0.12K. We discuss possible explanations, including effects related to magnetic impurities (Nd3+) and two-band superconductivity. |
Thursday, March 8, 2018 9:36AM - 9:48AM |
R09.00007: Complex polarization topologies in a confined PbTiO3 layer Shang-Lin Hsu, Margaret McCarter, Zijian Hong, Y. L Tang, SUJIT DAS, A. Ghosh, Javier Junquera, Long-Qing Chen, Lane Martin, Ramamoorthy Ramesh The manipulation of charge and lattice boundary conditions of atomically precise low-dimensional complex oxide heterostructures can stabilize ferroelectric topologies such as polar vortices and skyrmion-like bubble domains. Recent discovery the continuous rotation of clockwise/counterclockwise ferroelectric vortices were observed in ferroelectric/paraelectric (PbTiO3)n/(SrTiO3)n superlattices on the DyScO3 substrate. In this work, we reduce the complexity of the ferroelectric/paraelectric superlattice to the study of a model system of a single confined PbTiO3 layer on different substrates. We will present experimental-theoretical study of the emergence of complex topologies of electrical polarization. Phase-field modeling predicts a systematic evolution of the polarization states corresponding to different strain conditions of the substrates and second principle calculation predicts the polar distribution of electrical topologies. By changing strain conditions, we characterize from polar vortices to skyrmion-like bubble domains by high resolution scanning transmission electron microscopy in conjunction with piezoelectric force microscopy study of ferroelectric structure and reciprocal space mapping study of domain periodicity. |
Thursday, March 8, 2018 9:48AM - 10:00AM |
R09.00008: Role of dimensionality in SrIrO3/BaTiO3 superlattices David Howe, Mohammad Saghayezhian, Hangwen Guo, Zhen Wang, Yimei Zhu, E Plummer, Jiandi Zhang Ultrathin film SrIrO3 is unique among transition metal oxides because it has been shown to have strong spin-orbit coupling and electron-electron (e-e) correlations. Previous studies have found that a ferromagnetic and insulating phase in the SrIrO3/SrTiO3 superlattice appears when the SrIrO3 layer thickness is below 3 unit cells, which is attributed to enhanced e-e correlation as is expected for a system with reduced dimensionality. However, as we present here, the superlattice of SrIrO3/BaTiO3 does not show any thickness-driven MIT or ferromagnetism even in the single SrIrO3 unit cell superstructure. Our results demonstrate that other variables in addition to the enhanced e-e correlations, such as lattice structure effects, are crucial for the realization of magnetism and MIT’s in SrIrO3 systems. |
Thursday, March 8, 2018 10:00AM - 10:12AM |
R09.00009: Modulation doping in LaNiO3/SrIrO3 superlattices from first principles Michele Kotiuga, Heung Sik Kim, David Vanderbilt, Karin Rabe Doping is commonly used to tune and optimize material properties such as conductivity and optical properties. Doping at extremely high concentrations, at the level of an electron per formula unit, can stabilize novel phases. Here we study lanthanum nickelate (LaNiO3)/strontium iridate (SrIrO3) superlattices using the first-principles density functional theory (DFT) +U method, focusing on the 1/1 superlattice. For this superlattice we find that there is a modulation doping effect where electrons are transferred from the SrIrO3 layers to the LaNiO3 layers, converting nickels from Ni3+ to Ni2+ in the electron-doped LaNiO3 layers and and iridiums from Ir4+ to Ir5+ in the hole-doped SrIrO3 layers. We will present results on the orbital occupations and low energy structures, with the possibility for charge ordering, as well as the electronic and magnetic structures. To elucidate the behavior of the interfaces within these heterostructures, we present and analyze results for additional superlattices, including the 1/2 and 1/3 superlattices. |
Thursday, March 8, 2018 10:12AM - 10:24AM |
R09.00010: Strain Effects on Structural and Magnetic Properties of SrIrO3/SrTiO3 Superlattice Tamene R Dasa, Lin Hao, Liu Jian, Haixuan Xu Combining first principles technique with experimental studies, the effects of strain on the structural and magnetic properties of 1(SrIrO3)-1(SrTiO3) (SIO-STO) are investigated. The SIO-STO superlattice has a stable a-b-c- rotational pattern, from density functional theory calculations, and it is consistent with X-ray diffraction measurements. The structural responses, including octahedra rotation and tilting, as a function of epitaxial strain are established. The Ir atoms form a stable in-plane anti-ferromagnetic configuration with moderate spin canting. In this study, we find that tensile strain significantly increases the in-plane octahedral rotation and the exchange anisotropy, suggesting a prominent magnetoelastic coupling in SIO-STO. In addition, the strain-induced variation of orbital moment is significantly larger than that of the spin moments. The interplay among structural distortions, spin canting and Dzyaloshinskii-Moriya interaction is analyzed to provide a fundamental understanding of such magnetoelastic behavior in SIO-STO superlattice. |
Thursday, March 8, 2018 10:24AM - 10:36AM |
R09.00011: Non-Fermi Liquid Behavior and Topological Hall Effect in SrRuO3 Kaveh Ahadi, Patrick Marshall, Susanne Stemmer Here we report on the non-Fermi liquid behavior in high quality single crystal SrRuO3 thin films grown by hybrid molecular beam epitaxy. SrRuO3 thin films show metallic behavior down to helium liquid temperature. All samples show negative longitudinal magnetoresistance with a hysteresis appearing below 130 K. Furthermore, field cooling magnetization measurement confirms a drastic enhancement in magnetic signal at the same temperature. The resistivity data from 2 K to 40 K, using the general expression R(T)=R0+ATn for transport, resolves n=2 at low temperature (2 K) and n=1.5 at high temperature (40 K) with a smooth transition in between. Sweeping out-of-plane magnetic field (0-8 T) at different temperatures shows a drop in “n” and, concurrently, an enhancement in temperature coefficient at ~ 3 T. The temperature coefficient is directly proportional to carrier mass and the enhancement in “A” hints that carriers are getting heavier. An anomalous Hall effect (AHE) roughly ten times stronger that ordinary Hall effect (OHE) dominates the Hall signal at low fields. Finally, a topological Hall effect (THE) feature can be resolved superimposed on the AHE and OHE signals. |
Thursday, March 8, 2018 10:36AM - 10:48AM |
R09.00012: Anomalous Hall Effect in SrRuO3/SrIrO3 Heterostructures Dirk Groenendijk, Carmine Autieri, Thierry van Thiel, Nicolas Gauquelin, Johan Verbeeck, Silvia Picozzi, Andrea Caviglia Atomic-scale reconstructions at transition metal oxide interfaces can produce electronic and magnetic phases that are absent in the bulk constituents. Of particular interest are heterostructures of itinerant ferromagnets and materials with strong spin-orbit coupling (SOC), which can show interfacial reconstructions of electronic and magnetic properties. In this work, we examine the anomalous Hall effect (AHE) in transition metal oxide heterostructures composed of ultrathin SrRuO3 and SrIrO3. We find that, close to the sign-reversal temperature, the AHE can be modelled by two parallel channels producing Hall voltages of opposite sign. The different coercive fields allow control of the spin polarization of the two channels at fixed temperature, providing evidence of interlayer coupling. We propose that the strong SOC of the SrIrO3 modifies the band structure and associated Berry curvature of the top SrRuO3 layers near the SrRuO3/SrIrO3 interface. |
Thursday, March 8, 2018 10:48AM - 11:00AM |
R09.00013: Tuning the electrical properties of superconducting Sr2RuO4 thin films by epitaxy Jacob Ruf, Hari Nair, Nathaniel Schreiber, Ludi Miao, Darrell Schlom, Kyle Shen The superconducting phase of Sr2RuO4 is known to be unconventional and most likely odd-parity, but also the most sensitive to disorder of all known superconductors, requiring mean free paths of order ~ 100 nanometers. This has prompted work employing disorder-free knobs, such as externally applied strain both in single crystals and thin films, to manipulate and better understand the nature of the superconducting state that condenses from the low-temperature Fermi liquid in this multi-band system. Here we present a combination of x-ray diffraction and electrical transport measurements on strained thin films of Sr2RuO4 synthesized by molecular-beam epitaxy on various substrates and orientations to explore how the template set by the substrate can be used to control both the crystalline and defect structure of the films, as well as the material’s electronic response. Specifically, we probe how the substrate-induced lattice strain and planar defects modify the inelastic (electron-electron) and elastic (electron-disorder) scattering contributions to the electrical resistivity and anisotropy, and study their subsequent effects on superconductivity. |
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