Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session P37: Correlated Electrons in Nickelates and ManganitesFocus Live
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Sponsoring Units: GMAG DMP DCOMP DCMP Chair: Matthew Krogstad, Argonne National Laboratory |
Wednesday, March 17, 2021 3:00PM - 3:12PM Live |
P37.00001: Intertwined Density Waves in a Metallic Nickelate Junjie Zhang, Daniel Phelan, Hong Zheng, Stephan Rosenkranz, Raymond Osborn, Antia Botana, Yiming Qiu, Matthew Krogstad, Yu-sheng Chen, Jose A. Rodriguez-Rivera, Suyin Wang, Michael Ray Norman, John Mitchell Nickelates are a rich class of materials, ranging from insulating magnets to superconductors. But for stoichiometric materials, insulating behavior is the norm, as for most late transition metal oxides. Notable exceptions are the 3D perovskite LaNiO3, an unconventional paramagnetic metal, and the layered Ruddlesden-Popper phases R4Ni3O10, (R=La, Pr, Nd). The latter are particularly intriguing because they exhibit an unusual metal-to-metal transition. Here, we demonstrate that this transition results from an incommensurate density wave with both charge and magnetic character that lies closer in its behavior to the metallic density wave seen in chromium metal than the insulating stripes typically found in single-layer nickelates like La2-xSrxNiO4. We identify these intertwined density waves as being Fermi surface-driven, revealing a novel ordering mechanism in this nickelate that reflects a coupling among charge, spin, and lattice degrees of freedom that differs not only from the single-layer materials, but from the 3D perovskites as well. |
Wednesday, March 17, 2021 3:12PM - 3:24PM Live |
P37.00002: Low spin configuration and giant orbital polarization of Ni2+ in square planar environment Prithwijit Mandal, RANJAN PATEL, Dibyata Rout, Rajdeep Banerjee, Rabindranath Bag, koushik karmakar, Awadhesh Narayan, John Freeland, Surjeet Singh, Srimanta Middey The high Tc superconductivity in nickelates has been finally discovered in Sr0.2Nd0.8NiO2, in which Ni is in square planar (D4h) coordination of oxygen. Despite being iso-electronic (3d9), the parent compounds of nickelate and cuprate superconductors have markedly different electronic and magnetic behavior. To understand this, we have investigated the electronic and magnetic structure of Sr2CuO3 and Sr2Cu0.9Ni0.1O3. These compounds provide a unique opportunity to compare the electronic structure of both Ni and Cu in square planar (D4h) environment. Polarization-dependent X-ray absorption spectroscopy (XAS) at Ni L3,2 edge revealed extremely large (∼ 63%) orbital polarization (OP) for Ni. Our simulations based on multiplet ligand field theory for polarization dependent XAS of Ni2+ and the results from ab initio density functional theory have revealed that such high orbital polarization arises due to two holes in Ni 3dx2-y2 that give rise to nonmagnetic S = 0 state of Ni2+ - in contrast to S = 1 state from Hund’s first rule. Such nonmagnetic S = 0 Ni2+ in hole dope nickelate would be analogous to the Zhang Rice singlet. |
Wednesday, March 17, 2021 3:24PM - 3:36PM Live |
P37.00003: Epitaxial strain on nickelate RNiO3 thin films (R = Nd1-xSrx, La1-xNdx) Gregorio Ponti, Jonathan D. K. Tebo, Alexander Barajas, John T. Markert We report x-ray diffraction and resistivity measurements on strained nickelate thin films. Following the discovery of superconductivity in a nickelate[1] in an apparently hole-doped RNiO2 (“infinite-layer”) film (with R ≈ Nd0.8Sr0.2), after CaH2 reduction, subsequent studies stressed the importance of lattice mismatch[2,3]. We discuss the optimization of RNiO3 (R = Nd1-xSrx, La1-xNdx) thin films under varying epitaxial strain, induced by choice of substrate or buffer layer lattice constant, including RAlO3 (3.72-3.78 Å), SrTiO3 (3.905 Å), and R2CuO4 (3.91-3.96 Å). We study the effects of oxygen pressure during growth and film thickness on the electrical resistivity of these lattice-strained films in an effort towards superconducting RNiO2 thin films. |
Wednesday, March 17, 2021 3:36PM - 3:48PM Live |
P37.00004: Electronic-structural interplay in correlated materials with site- and orbital- selective Mott states: an embedded dynamical mean field theory perspective Gheorghe Pascut, Jennifer B Coulter, Premala Chandra, Karin M Rabe, Kristjan Haule Over the last decade, by using the Density Functional Theory (DFT) with Embedded Dynamical Mean Field Theory (eDMFT), it has been shown that novel electronic states with site- and orbital-selectivity exist at finite temperatures in correlated oxides materials such as CaFeO3, NdNiO3, LaMnO3, BiMnO3, TM2Mo3O8 (TM=Mn, Fe, Co, Ni, Zn). The recent development of forces for structural relaxations within the DFT+eDMFT opens a new avenue for the study of the method's predictive powers for the electronic-structural interplay at finite temperatures in correlated materials. In this talk we will discuss about the predictive powers of the DFT+eDMFT for the electronic-structural interplay for novel electronic states of matter in the materials mentioned above, where (I) Mott and metallic orbitals coexist (orbital-selective Mott state), (II) Mott, metallic and semi-metallic orbitals coexist (site-orbital-selective Mott state) and (III) Mott and band orbitals coexist (site-orbital-selective Mott state). |
Wednesday, March 17, 2021 3:48PM - 4:00PM Live |
P37.00005: Unusual effects of magnetic dilution in the ferrimagnetic columnar ordered Sm2MnMnMn4–xTixO12 perovskites Anuradha Vibhakar, Dmitry Khalyavin, Pascal Manuel, Ran Liu, Kazunari Yamaura, Alexei Belik, Roger D Johnson Powder neutron diffraction experiments have been employed to establish the effects of site-selective magnetic dilution in the Sm2MnMnMn4–xTixO12 A-site columnar ordered quadruple perovskite manganites (x = 1, x = 2 and x = 3). We show that in all three compositions the Mn ions adopt a collinear ferrimagnetic structure below 27 K, 62 K and 34 K, respectively. An unexpected increase in the ordering temperature was observed between the x = 1 and x = 2 samples, which indicates a considerable departure from mean field behaviour. This result is corroborated by large reductions in the theoretical ground state magnetic moments observed across the series, which indicate the presence of spin fluctuations and or disorder. We show that long range magnetic order in the x = 3 sample, which occurs below the percolation threshold for B-B exchange, can only be understood to arise if magnetic order in Sm2MnMnMn4–xTixO12 is mediated via both A-B and B-B exchange, hence confirming the importance of A-B exchange interactions in these materials. Finally we show that site-selective magnetic dilution enables the tuning of a ferrimagnetic compensation point and the introduction of temperature-induced magnetization reversal. |
Wednesday, March 17, 2021 4:00PM - 4:12PM Live |
P37.00006: Understanding the metal-to-insulator transition in La1-xSrxCoO3−δ and its applications for neuromorphic computing Shenli Zhang, Giulia Galli Transition metal oxides that exhibit a metal-to-insulator transition (MIT) as a function of oxygen vacancy concentration are promising systems to realize energy-efficient platforms for neuromorphic computing. However, the current lack of understanding of the microscopic mechanism driving the MIT hinders the realization of effective and stable devices. Here we investigate defective cobaltites and we unravel the structural, electronic and magnetic changes responsible for the MIT when oxygen vacancies are introduced in the material using first principle calculations. We show that, contrary to accepted views, cooperative structural distortions instead of local bonding changes are responsible for the MIT, and we describe the subtle interdependence of structural and magnetic transitions. Finally, we present a model, based on first principles, to predict the required electric bias to drive the transition, showing good agreement with available measurements and providing a paradigm to establish design rules for low-energy cost devices. [1] |
Wednesday, March 17, 2021 4:12PM - 4:24PM Live |
P37.00007: Magnetism and Transport in Novel High-Pressure Phases of Iron-Oxides Ghanashyam Khanal, Denis M. Vasiukov, Kristjan Haule After the recent discovery of the high-pressure phase of Fe$_4$O$_5$, studies of the high-pressure (HP) iron oxides with unusual stoichiometries have attracted a lot of interest. These systems have a mixed-valence state of iron ions with a characteristic charge-ordering at low temperature. However, there is still a lack of knowledge for many basic properties in these systems. We study a number of compounds from the homologous series (nFeO mFe$_2$O$_3$) using Density Functional Theory (DFT) + embedded Dynamical Mean-Field Theory (eDMFT) functional method to understand the electronic structure, magnetic and transport properties. Our calculations have shown that the there is an anisotropy in the optical conductivity and the anisotropy strongly increases along the direction of the infinite chain of trigonal prism in the magnetically ordered phase of HP Fe$_3$O$_4$. Along with that we also found that there is an orbital selective Mott state in the paramagnetic phase which disappears upon magnetic ordering. |
Wednesday, March 17, 2021 4:24PM - 4:36PM Live |
P37.00008: Properties of La0.7Ca0.3MnO3 under extreme tensile strength studied using Monte Carlo simulations Cengiz Sen, Elbio Dagotto In a recent groundbreaking experiment, membranes of the perovskite manganite La0.7Ca0.3MnO3 (LCMO) deposited on a flexible polymer layer were strained up to 8% (S. S. Hong et al., Science 368, 71 (2020)), much more than achieved by regular strain induced by a rigid substrate. By increasing this strain a metal-insulator transition was reported. Here we reproduce the results of the experiments using Monte Carlo simulations of the two-orbital double-exchange model including Jahn-Teller distortions, at hole density x=1/3. The full phase diagram with varying temperature and Jahn-Teller coupling is presented. A metal-insulator transition is found in our simulations, between a ferromagnetic metallic state with uniform charge distribution and an insulator with diagonal charge stripes that retains its ferromagnetic character. In between the hole-rich diagonals, staggered orbital order occurs (C. S. and E. Dagotto, Phys. Rev. B 102, 035126 (2020)). |
Wednesday, March 17, 2021 4:36PM - 4:48PM Live |
P37.00009: CaMn2O4-d a possible multiferroic candidate, an annealing study Melissa Gooch, Hung-Cheng Wu, Liangzi Deng, Hung-Duen Yang, Ching W Chu Over the last few years, manganese oxides have experienced a considerable increase in research interests due to their rich and complex phase diagrams, resulting from the flexibility of the manganese ions oxidations states. Ca-Mn-O is an excellent example, whose rich phase diagram also contains phases that have been theoretically predicted to be multiferroic. While many of the phases have been well investigated, CaMn2O4 to date is still not well understood and a hopeful candidate. |
Wednesday, March 17, 2021 4:48PM - 5:24PM Live |
P37.00010: Emergent Behavior in Ni1+-Rich Layered Nickelates Invited Speaker: John Mitchell For more than 30 years nickel oxides have been explored in vain as potential cuprate-like superconductors. The recent report of superconductivity in a nickelate film by Hwang et al (Nature 572, 624 (2019)) brings new urgency to this quest. Unlike that of their cuprate analogs, the electronic phase diagram of layered nickelates, R2-xSrxNiO4 (R=rare earth) is populated not by metals and superconductors, but rather with insulating charge- and spin-stripe phases. The absence of superconductivity can be rationalized by factors such as d-p mixing, lack or planar orbital polarization, among others. Each of these traces ultimately to the markedly different electronic configuration of d8 Ni2+ in octahedral coordination vis-à-vis d9 Cu2+ in an essentially square planar environment. Ni1+-containing solids are rare and difficult to synthesize. However, a family of such materials with square planar Ni does exist, with formula Rn+1NinO2n+2, where the Ni1+ fraction is given by (n-1)/n. Indeed, the reported nickelate superconductor thin film derives from the Sr-doped ‘infinite layer’ endmember of this series, Nd0.8Sr0.2NiO2. Here we discuss the phase behavior of the n=3 member of this series, R4Ni3O8(R=La,Pr) made possible by advances in high pressure crystal growth. Specifically, we show the emergence in this system of several characteristics of cuprates that have been missing in nickelates, including strong in-plane x2-y2 orbital polarization, significant 3d-2p mixing at Ef, and competition between metallic and antiferromagnetic insulating stripe phases. We present an expanded phase diagram of the reduced, layered nickelates and suggest ways in which these materials might be made superconductors. |
Wednesday, March 17, 2021 5:24PM - 5:36PM Live |
P37.00011: Magnetic structure of perovskite-derived LaNiO3-δ nickelate with ordered oxygen vacancies Yongjin Shin, James M Rondinelli Rare-earth nickelates perovskites (RNiO3, with R=rare earth) are a family of compounds exhibiting temperature-dependent metal-insulator transitions with octahedral breathing distortion, while LaNiO3 is an exception and lacks this distortion. Instead, oxygen-deficient LaNiO3-δ exhibits electronic/magnetic transitions with varying oxygen content δ owing to the reducibility of Ni3+. Specifically, a metal-semiconductor-insulator transition occurs concurrently with a paramagnetic-ferromagnetic-antiferromagnetic transition in bulk materials as δ varies [1]. Here, we explain the electronic structure of LaNiO2.5 and LaNiO2.75 and their stable magnetic orders using first-principles calculations. We find square planar NiO4 units formed by ordered oxygen vacancies are electronically and magnetically inactive, which along with changes in the NiO6 connectivity, govern the phase transitions. Specifically, we discovered a columnar-type breathing distortion in LaNiO2.75 with zigzag-type magnetic order. We conclude with model interpretations of the non-equilibrium states reported for LaNiO2.5 and LaNiO3, and their connection to experimental observations. |
Wednesday, March 17, 2021 5:36PM - 5:48PM Live |
P37.00012: Ultrafast spin-nematic and ferroelectric phase transitions in a photo-induced charge and orbital ordered manganite Sangeeta Rajpurohit, Liang Tan, P. E. Blöechl Manganites are a class of materials in which charge, spin, and lattice degrees are strongly coupled and known to actively participate in the energy conversion processes. Experimental studies of optical manipulation of spin orders in manganites show these systems are promising materials for the opto-spintronics. However, the intrinsic mechanisms governing the photo-induced magnetic phase transitions are not very well understood and require microscopic knowledge of the energy conversion processes. The time and length scales of the phonon and spin dynamics in such systems are beyond the scope of the traditional first-principles approaches, such as TD-DFT. Combining a tight-binding model with Ehrenfest dynamics, we studied the photo-excitation and the subsequent non-equilibrium dynamics in charge- and orbital-ordered manganites. We propose a mechanism for the optical excitation of a non-collinear antiferromagnet leading selectively to new spin orders beyond a critical light-intensity. The optical excitations produce two distinct and highly interesting novel phases; a spin-nematic and a ferroelectric phase. A specific phase is selected by the polarization of the light pulse. |
Wednesday, March 17, 2021 5:48PM - 6:00PM Live |
P37.00013: The Role of Phonons and Defects in the Recently Discovered Non-Cubicity of SrVO3 Tanya Berry, Allyson Fry-Petit, Mekhola Sinha, Qiang Zhang, Gudrun Auffermann, Tyrel McQueen, Sven Peter Rudin, William Phelan The correlated nature of SrVO3 underlies its potential for advanced applications that include transparent conductors used in photovoltaics and low work-function technologies like electron emitters. While its interesting electronic nature and functionalities have been widely studied, the finer details of the lattice dynamics and structure of SrVO3 (to date only the cubic perovskite form has been observed) relative to its ferroelectric (BaTiO3) and quantum paraelectric (SrTiO3) cousins have largely eluded both the chemistry and physics communities. Motivated by reports of imaginary phonon modes in DFT calculations of cubic SrVO3 and employing high quality neutron scattering data, we indeed find that the neutron diffraction and corresponding pair distribution function of SrVO3 over a range of temperatures are better modeled to lower symmetry structures. Contrary to previous work, our DFT calculations show that the non-cubicity of SrVO3 does not result from lattice instabilities but rather defects likely introduced from common synthesis procedures. |
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