Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session A12: Focus Session: Complex Oxide Interfaces - Nickelates |
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Sponsoring Units: DMP Chair: Prasana Balachandran, Drexel University Room: 314 |
Monday, March 18, 2013 8:00AM - 8:12AM |
A12.00001: Designing a Spin-one Mott Insulator: Complete Charge Transfer in Nickelate-Titanate Heterostructures Hanghui Chen, Chris Marianetti, Andrew Millis $Ab$ $initio$ calculations are performed to show that complete charge transfer may occur from the TiO$_2$ to the NiO$_2$ layers in (LaTiO$_3$)$_1$/(LaNiO$_3$)$_1$ superlattices. Although the two component materials are an $S = 1/2$ Mott insulator and a weakly correlated paramagnetic metal, strong correlation effects on Ni $d$ states can render the superlattice an unusual $S = 1$ charge transfer insulator, with the Ti-$d$ band empty, the Ni in the $d^8$ state and the oxygen bands filled. The charge transfer gap is set by the Ti/Ni $d$ level splitting. Magnetic, photoemission and x-ray scattering experiments are suggested to test the theory. The results show that heterostructuring can lead to very high levels of electron doping of oxides. [Preview Abstract] |
Monday, March 18, 2013 8:12AM - 8:24AM |
A12.00002: Two dimensional Mott physics in the rare earth nickelates Ankit Disa, Divine Kumah, Joseph Ngai, Jarrett Moyer, Fred Walker, Charles Ahn The strong electron correlations inherent in the rare-earth nickelate system (RNiO$_{3}$) lead to a metal-insulator transition, the temperature of which can be tuned by changing the rare-earth ion, R. Bulk LaNiO$_{3}$ is metallic at all temperatures, and NdNiO$_{3}$ undergoes a metal-insulator transition at 150 K. However, reducing the thickness of both LaNiO$_{3}$ and NdNiO$_{3}$ strongly affects the transport behavior, where LaNiO$_{3}$ undergoes a thickness-driven metal-insulator transition below $\sim$4 unit cells. Here, we identify the physics of this transition and demonstrate two-dimensional metallic behavior in thin films. We show that by direct chemical doping of LaNiO$_{3}$ thin films we can restore metallic behavior and tune the conductivity. We apply the same technique to thin films of NdNiO$_{3}$ and control the metal-insulator transition temperature. Finally, combining artificial confinement and doping, we observe metallicity in nickelate layers as thin as two unit cells. The effects of both structural and charge-carrier modifications on the transport properties of the thin films will be discussed. [Preview Abstract] |
Monday, March 18, 2013 8:24AM - 8:36AM |
A12.00003: Epitaxial growth of (111)-oriented LaAlO$_3$/LaNiO$_3$ ultra-thin superlattices S. Middey, D. Meyers, M. Kareev, E.J. Moon, B.A. Gray, J.W. Freeland, J. Chakhalian The epitaxial stabilization of a single layer or superlattice structures composed of complex oxide materials on polar (111) surfaces is severely burdened by reconstructions at the interface, that commonly arise to neutralize the polarity. We report on the synthesis of high quality LaNiO$_3$/mLaAlO$_3$ pseudo cubic (111) superlattices on polar (111)-oriented LaAlO$_3$, the proposed complex oxide candidate for a topological insulating behavior. Comprehensive X-Ray diffraction measurements, RHEED, and element specific resonant X-ray absorption spectroscopy affirm their high structural and chemical quality. The study offers an opportunity to fabricate interesting interface and topology controlled (111) oriented superlattices based on ortho-nickelates. [Preview Abstract] |
Monday, March 18, 2013 8:36AM - 9:12AM |
A12.00004: Topological phases in complex oxide interfaces and heterostructures Invited Speaker: Gregory A. Fiete In this talk we highlight recent theoretical work from our group aimed at identifying complex oxide interfaces and heterostructures that are expected to support topological phases, namely the $Z_2$ time-reversal invariant topological insulator and the zero magnetic field Chern insulator, or quantum anomalous Hall state. We focus on two particular systems: (1) Perovskites of the form ABO$_3$ and (2) Pyrochlores of the form A$_2$B$_2$O$_7$ where A is usually a rare earth element and B is a transition metal element. One of our main results is that thin film growth along the [111] direction is favorable for the realization of topological phases in experiment. We lay out the most important film properties that appear to favor topological phases and discuss the different physics associated with realizing topological phases in 3d, 4d, and the heaviest 5d-based transition metal oxide systems. Key open questions and experimental challenges are presented, as well as the potential advantages that oxide systems offer over the Bi-based topological insulator material class in device applications. [Preview Abstract] |
Monday, March 18, 2013 9:12AM - 9:24AM |
A12.00005: Controlling the metal insulator transition using the ferroelectric field effect in rare earth nickelates Matthew Marshall, Ankit Disa, Divine Kumah, Hanghui Chen, Sohrab Ismail-Beigi, Fred Walker, Charles Ahn A ferroelectric field effect transistor (FE-FET) modulates conductivity in a non-volatile manner by electrostatically accumulating and depleting charge carriers at the interface between a conducting channel and ferroelectric gate. The rare earth nickelate LaNiO$_{3}$ is metallic in bulk, while other rare earth nickelates, such as NdNiO$_{3}$, exhibit metal-insulator transitions and anti-ferromagnetic behavior in the bulk. Here, we show that by coupling the ferroelectric polarization of Pb$_{0.8}$Zr$_{0.2}$TiO$_{3}$ (PZT) to the carriers in a nickelate, we can dynamically induce a metal- insulator transition in ultra-thin films of LaNiO3, and induce large changes in the MIT transition temperature in NdNiO3. Density functional theory is used to determine changes in the physical and electronic Ni-O-Ni bond angle of the nickelate at the interface between PZT and LaNiO3. The effect of the ferroelectric polarization is to decrease the Ni-O-Ni bond angle from 180 degrees and increase the carrier effective mass. Related to this change in electronic structure, we observe a change in resistivity of approximately 80{\%} at room temperature for an ultra-thin 3 unit cell thick film of LaNiO$_{3}$. [Preview Abstract] |
Monday, March 18, 2013 9:24AM - 9:36AM |
A12.00006: Atomic-scale structure and composition mapping in nickelate heterostructures Divine Kumah, Ankit Disa, Joseph Ngai, Hanghui Chen, Sohrab Ismail-Beigi, Charles Ahn, Fred Walker Strongly correlated electronic systems display a wide range of interesting properties, including ferroelectricity, superconductivity, metal-insulator transitions, and novel magnetic phenomena. The electrical and magnetic properties of thin film heterostructures based on these systems are directly linked to their atomic scale structure and composition. This link is important for the rare earth nickelates, which exhibit first-order metal-insulator transitions, antiferromagnetism, and charge ordering. At the interfaces present in these systems, structural coupling can lead to new effects. We use a synchrotron-based resonant anomalous x-ray scattering method to elucidate the physical and electronic structure at complex oxide heterointerfaces of nickelates grown using molecular beam epitaxy. Temperature dependent resonant x-ray studies in doped 8 unit-cell thick NdNiO$_3$ films reveal subtle changes in atomic structure and Ni charge disproportionation at the metal-insulator transition. [Preview Abstract] |
Monday, March 18, 2013 9:36AM - 10:12AM |
A12.00007: Ultrafast phase control in complex oxide heterostructures Invited Speaker: Andrea Caviglia Complex oxide heterostructures have emerged as multifunctional materials of striking flexibility, in which unconventional electronic phases can be realised by engineering the strain field across interfaces. This same mechanical coupling is also expected to be effective on the ultrafast timescale, and could be exploited for the dynamic control of materials properties. Here, we demonstrate that a large-amplitude mid-infrared field, made resonant with a stretching mode of the substrate, can switch the electronic properties of a thin film across an interface. Exploiting dynamic vibrational propagation between different components of a heterostructure, insulating antiferromagnetic NdNiO$_3$ is driven through a prompt, five-order-of-magnitude increase of the electrical conductivity, with resonant frequency and susceptibility that is controlled by choice of the substrate material. Vibrational phase control, extended here to a wide class of heterostructures and interfaces, may be conducive to new strategies for electronic phase control at THz repetition rates. [Preview Abstract] |
Monday, March 18, 2013 10:12AM - 10:24AM |
A12.00008: Investigation of Nonlinear Differential Conductance in NdNiO$_{3}$ Thin Films Will Hardy, Heng Ji, Junwoo Son, Susanne Stemmer, Douglas Natelson We will report on recent investigations of the voltage and temperature dependence of the nonlinear differential conductance, dI/dV, of the insulating state in thin films of NdNiO$_{3}$. This compound exhibits a metal-insulator transition near 100 K [1] between a high temperature paramagnetic metal and a low temperature charge-transfer insulator. These investigations are motivated by previous observations in Fe$_{3}$O$_{4}$, a strongly correlated material that undergoes the Verwey transition at a similar temperature scale, in which hysteretic, voltage-driven breakdown of the insulating state has been reported [2]. We examine the evolution of the nonlinear conductance, as well as its dependence on the device geometry, in planar devices at temperatures near the transition.\\[4pt] [1] Son, Junwoo, Bharat Jalan, Adam P. Kajdos, Leon Balents, S. James Allen, and Susanne Stemmer. ``Probing the Metal-Insulator Transition of NdNiO$_{3}$ by Electrostatic Doping.'' App. Phys. Lett. 99, 192107 (2011).\\[0pt] [2] Fursina, A.A., R.G.S. Sofin, I.V. Shvets, and D. Natelson. ``The Origin of Hysteresis in Resistive Switching in Magnetite is Joule Heating.'' Phys. Rev. B 79, 245131 (2009). [Preview Abstract] |
Monday, March 18, 2013 10:24AM - 10:36AM |
A12.00009: Strain mediated suppression of the metal-insulator and anti-ferromagnetic transition in EuNiO3 thin films Derek Meyers, Srimanta Middey, Mikhail Kareev, Benjamin Gray, John Freeland, Jak Chakhalian Ultrathin epitaxial films of EuNiO$_3$ were grown on a series of substrates traversing highly compressive (-2.4\%) to highly tensile (2.5\%) lattice mismatch. X-ray absorption spectroscopy measurements revealed a strong multiplet splitting in the tensile samples that progressively weakens with increasing compressive strain. Transport measurements further collaborated these findings, showing a successively (from tensile to compressive) lower resistance and a complete suppression of the metal-insulator transition at -2.4\% lattice mismatch. The derivative of the transport showed a strong downturn around the bulk Neel temperature, which was also suppressed with compressive strain. [Preview Abstract] |
Monday, March 18, 2013 10:36AM - 10:48AM |
A12.00010: Composition spread studies of Nd$_{1-x}$La$_{x}$NiO$_{3}$ combinatorial thin films Richard Suchoski, Kui Jin, Shintaro Yasui, Richard Greene, Ichiro Takeuchi Rare earth nickelates have attracted a great deal of attention in recent years due to a host of interesting features, one being a transition from paramagnetic metal to antiferromagnetic insulator through distortions from the ideal perovskite unit cell. This metal-to-insulator transition (MIT) can be manipulated by modifying variables such as temperature, rare earth ion size, oxygen content, or stress from lattice-mismatched epitaxial thin film growth. Research on this family has been extensive, though there still exists an absence of thin film studies focusing on intermediate compositions. We have fabricated epitaxial thin film composition spreads of Nd$_{1-x}$La$_{x}$NiO$_{3}$ grown via combinatorial PLD to investigate these transitional compositions. While our films exhibit a smooth composition progression, we observe a composition threshold where orthorhombic NdNiO$_{3}$ transforms to rhombohedral LaNiO$_{3}$, correlating with disappearance of the MIT, and displays a non-Vegard evolution of the film's in-plane lattice constant in HRXRD and Raman scattering data of the A$_{1g}$ rotational mode. [Preview Abstract] |
Monday, March 18, 2013 10:48AM - 11:00AM |
A12.00011: First-principles study of the properties of oxygen-deficient LaNiO$_{3-x}$ structures Andrei Malashevich, Sohrab Ismail-Beigi There has been a great deal of recent interest and activity regarding rare earth nickelates in bulk form, as superlattices, and as thin films. The parent nickelate in these cases is typically LaNiO$_3$, which in bulk form is a paramagnetic metal. In addition, due to its relatively good lattice match to other perovskites, it also serves as an electrode in functional oxide film devices. However, it is known that the conductivity of LaNiO$_3$ in any form is strongly affected by the presence of oxygen vacancies. Here, we present a first-principles study of a variety of oxygen-deficient LaNiO$_{3-x}$ structures. We describe our theoretical results for the atomic-scale geometry and energetics of the vacancies (formation and aggregation), their mobilities, and their electronic structure. [Preview Abstract] |
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