Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session D21: Nickelates and Other Transition Metal Oxides |
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Sponsoring Units: DCMP Chair: Jack Chakhalian, University of Arkansas Room: 201 |
Monday, March 2, 2015 2:30PM - 2:42PM |
D21.00001: Pseudo-gaps at the Mott quantum critical point in the perovskite rare earth nickelates S. James Allen, Adam Hauser, Evgeny Mikheev, Ankit Disa, Fred Walker, Nelson Moreno, Charles Ahn, Leon Balents, Susanne Stemmer, Susanne Stemmer We explore the behavior of the pseudo-gap in the vicinity of the quantum critical point of charge transfer Mott insulators. We focus on NdNiO3 and LaNiO3, which as bulk material bracket the quantum critical point, but tune the nature of the transition in epitaxial ultra-thin films by substrate strain, film thickness and Nd/LaNiO3 composition. We expand our earlier work [1] that documented the energy gaps and pseudo gaps in thick films using tunneling spectroscopy between Al and nickelate films with 1nm Al2O3 barriers. We focus on the relative importance of disorder scattering and electron correlation in the pseudogaps. \\[4pt] [1] ``Gaps and pseudo-gaps at the Mott quantum critical point in the perovskite rare earth nickelates,'' S. James Allen, Adam J. Hauser, Evgeny Mikheev, Susanne Stemmer et al., arXiv:1404.2544. [Preview Abstract] |
Monday, March 2, 2015 2:42PM - 2:54PM |
D21.00002: Carrier localization in correlated nickelates by electron doping You Zhou, Jian Shi, Shriram Ramanathan The electronic properties of transition metal oxides are often sensitive to the orbital occupancy of the \textit{3d} electrons due to non-degenerate energy levels and strong electron correlations. A prototypical rare earth nickelate, SmNiO$_{3}$ exhibits thermally driven insulator-metal transition at 400 K with one to two orders of magnitude change in its resistivity, characterized by charge ordering of the Ni sites. In this work, by modifying the $ e_{g}$ orbital filling of Ni through electron doping with reversible hydrogenation and lithium/magnesium intercalation, we realize a deep insulating phase with greater than eight orders of magnitude change in resistivity at room temperature. The band gap can be modulated by nearly 3 eV. We will consider the mechanisms leading to these striking observations in depth in this presentation. [Preview Abstract] |
Monday, March 2, 2015 2:54PM - 3:06PM |
D21.00003: Atomic-scale control of conductivity in complex oxide thin films Divine Kumah, Andrei Malashevich, Ankit Disa, Dario Arena, Fred Walker, Sohrab Ismail-Beigi, Charles Ahn Recent interest in ultra-thin oxide materials such as LaNiO3 as alternate channel materials for device applications has arisen due to their inherently high carrier densities, as well as the strong coupling of their electronic and magnetic order parameters to structural degrees of freedom. Understanding the structural-property relations in these systems is crucial for designing heterostructure devices for a wide range of applications including Mott field effect transistors. By combining atomic-layer synthesis, picometer-scale 3D imaging using synchrotron x-ray diffraction and first-principles theory, a correlation between the composition and charge of the surface atomic layer of thin LaNiO3 films and structural distortions which control film conductivity is found. We find that films terminated with positively charged LaO planes preserve bulk-like Ni-O bonding and are metallic. In contrast, films with thicknesses below 5 unit cells terminated with negatively charged NiO2-planes are insulating with strongly distorted Ni-O bonds. The differences in the observed structural distortions are understood in terms of a balance between the electrostatic and mechanical boundary conditions governing the two systems. [Preview Abstract] |
Monday, March 2, 2015 3:06PM - 3:18PM |
D21.00004: Electrically induced metal-insulator transition in epitaxial SmNiO$_{3}$ thin films Toyanath Joshi, Nikhil Shukla, Sandeepan DasGupta, Pavel Borisov, Suman Datta, David Lederman Materials with metal-insulator transitions (MITs) above room temperature are potentially interesting for electronic applications, inter alia, to design a new class of the so-called Mott field transistors. We studied a member of the rare-earth nickelates familiy, SmNiO$_{3}$, with the bulk MIT transition temperature close to 400K. Thin films of SmNiO$_{3}$ were grown using pulsed laser deposition. Epitaxial structural quality was verified by reflection high-energy electron diffraction, x-ray diffraction, x-ray reflectometry, x-ray photoelectron spectroscopy and atomic force microscopy. Temperature-dependent resistivity measurements showed MIT temperatures close to the bulk values. Electrically driven MIT in two terminal SmNiO3 thin film devices was demonstrated using DC and pulsed mode I-V measurements in the temperature range 273-348 K. The differential conductance \textit{dI/dV} peaked in the DC mode at switching field of 80 kV/cm at 273 K. The switching behavior became less pronounced with increasing measurement temperature and decreasing time period of the voltage pulses. By analysis of the experimental data we conclude the electrically-driven MIT in SmNiO$_{3}$ is due to the current-induced Joule self-heating. These findings should contribute to realization of novel electronic applications. [Preview Abstract] |
Monday, March 2, 2015 3:18PM - 3:30PM |
D21.00005: Anti-ferromagnetically driven Mott transition in ultrathin NdNiO3 epitaxial films Mikhail Kareev, D. Meyers, Jian Liu, S. Middey, J.W. Freeland, P. Ryan, J. Chakhalian The independent roles of anti-ferromagnetism and charge ordering in the realization of the temperature induced Mott metal-to-insulator transition within heteroepitaxial nickelate films remain to be disentangled hindering true understanding of the nature of the hotly debated ground state. To this end, we have investigated ultra thin, fully epitaxial films of the strongly correlated electron system NdNiO3 with hard and soft resonant x-ray scattering. We find a robust E0-type antiferromagnetic transition, identical to the bulk ordering, occurs despite the ultra thin nature of the films. However, many discrepancies with the bulk like charge ordering are found. [Preview Abstract] |
Monday, March 2, 2015 3:30PM - 3:42PM |
D21.00006: ABSTRACT WITHDRAWN |
Monday, March 2, 2015 3:42PM - 3:54PM |
D21.00007: Evolution of antiferromagnetic order in rare-earth nickelates probed by muon spin relaxation Benjamin Frandsen, Lian Liu, Sky Cheung, Yasutomo J. Uemura, Timothy Munsie, Murray Wilson, Alannah Hallas, Greame M. Luke, Bijuan Chen, Changqing Jin, Cui Ding, Fanlong Ning, Jose Alonso The rare-earth nickelates with structural formula $R$NiO$_3$ comprise a well-known family of Mott insulators that exhibits a gradual suppression of the metal-insulator transition and antiferromagnetic (AF) order with increasing rare-earth ionic size, resulting in a zero-temperature quantum phase transition at a rare-earth ionic radius of $\sim$1.17 \AA. We present detailed muon spin relaxation ($\mu$SR) measurements of $R$NiO$_3$ ($R$=Sm,Nd,Pr,La) to investigate the evolution of the antiferromagnetic order across the phase diagram. In the compounds with lower ordering temperatures near the quantum phase transition, we observe a ``stretched'' Mott transition with phase separation between magnetic and paramagnetic regions over a wide temperature interval. We also find that the suppression of the magnetic order at the quantum phase transition occurs in a first-order manner, with the ordered volume fraction decreasing to zero while the moment size remains large and constant. We compare these observations to other Mott insulator systems and discuss generic behavior. [Preview Abstract] |
Monday, March 2, 2015 3:54PM - 4:06PM |
D21.00008: Non-Gaussian resistance noise across the metal-insulator transition in epitaxial NdNiO3 films Ali Alsaqqa, Sujay Singh, Srimanta Middey, Michael Kareev, Jak Chakhalian, G. Sambandamurthy The rich phase diagrams exhibited by strongly correlated rare earth nickelates provide a great playground to investigate the electronic, magnetic and structural properties using a variety of experimental tools. NdNiO$_3$ thin films exhibit a temperature-driven metal-insulator transition (MIT) and the transition temperature is controlled by the interface strain. We present results from transport measurements and noise spectroscopy studies in strained, ultrathin (15 unit cells) NdNiO$_3$ films across the MIT. Resistance noise spectroscopy (in the frequency range below 10 Hz) is a powerful tool to statistically investigate the fluctuations of the microscopic scatterers that can dramatically affect macroscopic properties. In our samples, we find that the noise spectrum follows a 1/f behavior, however the noise magnitude dramatically changes across the MIT. We observe that the noise magnitude is Gaussian in the metallic phase and turns non-Gaussian in the insulating phase suggesting the importance of non-uniform scatterers. The individual roles of percolation events and/or correlation effects arising from closing of the charge transfer gap in the manifestation of noise behavior will be discussed. Results from both thermal-driven and electric field-driven transitions will be presented. [Preview Abstract] |
Monday, March 2, 2015 4:06PM - 4:18PM |
D21.00009: Nanostructure Investigations of Nonlinear Differential Conductance in NdNiO$_3$ Thin Films Will Hardy, Heng Ji, Evgeny Mikheev, Susanne Stemmer, Douglas Natelson Transport measurements on thin films of NdNiO$_3$ reveal a crossover to a regime of pronounced nonlinear conduction below the well-known metal-insulator transition temperature. The evolution of the transport properties at temperatures well below this transition appears consistent with a gradual formation of a gap in the hole-like Fermi surface of this strongly correlated system. As $T$ is decreased below the nominal transition temperature, transport becomes increasily non-Ohmic, with a model of Landau-Zener breakdown becoming most suited for describing $I(V)$ characteristics as the temperature approaches 2 K. [Preview Abstract] |
Monday, March 2, 2015 4:18PM - 4:30PM |
D21.00010: ABSTRACT MOVED TO J15.00013 |
Monday, March 2, 2015 4:30PM - 4:42PM |
D21.00011: ABSTRACT WITHDRAWN |
Monday, March 2, 2015 4:42PM - 4:54PM |
D21.00012: Comparative study of Raman excitations in YVOand HoVO Benoit Roberge, Serge Jandl, Agustinus Agung Nugroho, Thomas Palstra First-order Raman scattering and multiphonons are studied in RVO3(R$=$Ho and Y) as a function of temperature in the orthorhombic and monoclinic phases. Below T$_{\mathrm{OO}}=$ 200 K in YVO3 and T$_{\mathrm{OO}}=$ 188 K in HoVO3, a G-type orbital ordering (G-OO) with a concomitant monoclinic transition occurs. The orbital ordering enhances the phonon polarizabilities, it also allows the resolution of room-temperature phonons, and activates new excitations around 700 cm$^{-1}$. Below T$_{\mathrm{N}}=$ 114 K (in both compounds), a C-type magnetic ordering (C-SO) occurs and some phonon frequency softening or frequency hardening are observed. Following the structural (monoclinic to orthorhombic) and spin/orbital rearrangement (C-SO to G-SO and G-OO to C-OO) occuring at T$_{\mathrm{N2}}=$ 77 K in YVO3 and T$_{\mathrm{N2}}=$ 40 K in HoVO3, important changes are observed in Raman excitations of both compounds. Even if R ionic radii of HoVO3 and YVO3 are nearly equal (R$_{\mathrm{Ho}}=$ 192 pm and R$_{\mathrm{Y}}=$ 190 pm), we observe some differences that we report. [Preview Abstract] |
Monday, March 2, 2015 4:54PM - 5:06PM |
D21.00013: ABSTRACT WITHDRAWN |
Monday, March 2, 2015 5:06PM - 5:18PM |
D21.00014: Self-interaction corrected electronic structure of Ti4O7, TiO2 and Ti2O3 Xiaoliang Zhong, Ivan Rungger, Peter Zapol, Olle Heinonen Titanium oxides have a range of applications in, e.g., catalysis and resistive switching. There are many oxide structures with different ground states and electronic properties that have to be understood for potential applications to be possible. We have studied rutile TiO$_{2}$, Ti$_{2}$O$_{3}$, and Magn\'eli phase Ti$_{4}$O$_{7}$ using density functional theory with self-interaction corrections to account for electronic correlations, which are important in these structures. The ground state of the low temperature (LT) phase of Ti$_{4}$O$_{7}$ is found to be a new semiconducting state with antiferromagnetic coupling between two sublattices. Depending on the charge screening strength, different Ti-O phases are best described by applying different values of an empirical parameter $\alpha $, which represents the magnitude of the applied self-interaction correction. We will show that Pauli paramagnetism of the metallic high-temperature Ti$_{4}$O$_{7}$ phase is predicted using $\alpha \approx $0, that the band gaps of small-gap LT-Ti$_{4}$O$_{7}$ and Ti$_{2}$O$_{3}$ are captured by $\alpha \approx $0, while the large band gap of TiO$_{2}$ is reproduced using $\alpha \approx $0.9. Nevertheless, restricting $\alpha $ to the standard value of 0.5 for transition metal oxides is found to be a good compromise describing reasonably well the electronic structures of all these oxides. We gratefully acknowledge the computing resources provided on Blues, a high-performance computing cluster operated by the Laboratory Computing Resource Center at Argonne National Laboratory. Argonne National Laboratory's work was supported under U.S. Department of Energy contract DE-AC02-06CH11357. [Preview Abstract] |
Monday, March 2, 2015 5:18PM - 5:30PM |
D21.00015: ABSTRACT WITHDRAWN |
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