Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session R50: Correlated Transition Metal Oxides |
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Sponsoring Units: DCMP Chair: Liu Tjeng, Max Planck Inst Room: Mile High Ballroom 1C |
Thursday, March 5, 2020 8:00AM - 8:12AM |
R50.00001: Spin Hall magnetoresistance studies of differently strained ultrathin SrMnO3 films Arijit Das, Adam J Watson, Eswara phanindra Vallabhaneni, Tamalika Banerjee The ability to tune magnetic ordering in a nominally antiferromagnetic insulator, making use of the co-dependence of the charge, spin and orbital degrees of freedom in transition metal oxides, opens a vast playing field in the area of antiferromagnetic spintronics. We use Spin Hall magnetoresistance (SMR) as a probe of the magnetic ordering in thin films of SrMnO3 (SMO) when grown on two different substrates –SrTiO3 (STO) and LaAlO3 (LAO) -that changes the induced strain from tensile to compressive respectively. An in-plane magnetic field dependent angular measurement of the transverse resistivity of Pt Hall bars patterned on SMO films were studied for both cases. The compressively strained SMO film on LAO shows a 180o phase shift relative to the tensile strained SMO film on STO, suggesting a change in the magnetic ordering from antiferromagnetic to ferromagnetic. This is brought about by the presence of oxygen vacancies promoted by the underlying tensile strain in SMO on STO. This work shows the unique possibility of tailoring the magnetic properties in complex oxides with strain and the ability of interface spin-transport probes as SMR to fingerprint them, establishing their suitability for magnon transport studies. |
Thursday, March 5, 2020 8:12AM - 8:24AM |
R50.00002: Orbital wave in the Raman scattering cross section of LaMnO3 Purevdorj Munkhbaatar, Myung-Whun Kim We calculated the polarization-dependent Raman scattering cross-section spectra of LaMnO3 below the A-type magnetic ordering temperature. Two strong peaks appear around the MnO6 octahedra stretching phonon frequency. One mode shows Ag symmetry, while the other mode shows Bg symmetry. We found that the Ag symmetry peak is a Jahn-Teller phonon coupled to the orbital wave and the Bg symmetry peak is an orbital wave mode coupled to a Q2 phonon mode via the Jahn-Teller electron-phonon coupling. |
Thursday, March 5, 2020 8:24AM - 8:36AM |
R50.00003: Investigation of the Jahn-Teller transition in La1-xSrxMnO3 by single-crystal neutron diffuse scattering Hongze Li, Yaohua Liu, Jianshi Zhou The Jahn-Teller (JT) distortion occurs in a single valance system where a structural distortion is needed to lift the orbital degeneracy. In the mixed valance system La1-xSrxMnO3 (LSMO), the JT transition remains robust and sharp. It is not clear if the distribution of Mn3+ in Mn4+ matrix plays an important role. On cooling, LSMO undergoes the cooperative JT transition to order orbitals, spin ordering transition, and the charge ordering transition[1]. Pair distribution function analysis of neutron powder diffraction data has previously been done to discuss the role of polarons in the transition[2,3]. With single-crystal neutron diffuse scattering (NDS), we have observed patterns that show an interesting evolution as it is cooled through three transitions. Weak rod-shaped NDS features along L with even H+K above TJT get enhanced as the temperature is cooled below TJT, suggesting coherent scattering is developed above TJT. The NDS features disappear below the charge ordering transition temperature TCO, associated with the formation of superlattices. Potential models to interpret the observations will be discussed. |
Thursday, March 5, 2020 8:36AM - 8:48AM |
R50.00004: Visualization of Site- and Bond-Centered Charge Order in a Half-Doped Manganite Ismail El Baggari, David J. Baek, Michael J. Zachman, Di Lu, Yasuyuki Hikita, Elizabeth Nowadnick, Harold Hwang, lena Kourkoutis Charge order instabilities, the ordering of electrons and spins into periodic structures, occur in many classes of correlated quantum matter. Within a superlattice, charge-ordered states may have distinct electronic patterns and symmetries, however, distinguishing between them is challenging. In half-doped manganites, for instance, both site-centered (stripe) and bond-centered (bi-stripe) orders have been proposed. Using cryogenic scanning transmission electron microscopy, we map the charge-ordered structure in a Nd1/2Sr1/2MnO3 thin film by measuring picoscale periodic lattice distortions. We find two distinct ground states coexisting over tens of nanometers. The first is consistent with site-centered order. The second represents bi-stripes which remarkably are not purely bond-centered. The bi-stripes are intermediate between bond- and site-centered order and break inversion symmetry. |
Thursday, March 5, 2020 8:48AM - 9:00AM |
R50.00005: Probing Orbital Order in Magnetite with Resonant Elastic X-Ray Scattering Nelson Hua, Jianheng Li, Stjepan B Hrkac, Anatoly Shabalin, Andi Barbour, Wen Hu, Claudio Mazzoli, Stuart B Wilkins, Roopali Kukreja, Eric Fullerton, Oleg Shpyrko The underlying mechanism driving the metal-insulator transition in magnetite and the presence of charge order in the low-temperature insulating state remain unresolved since Verwey first discovered this transition back in 1939. Standard X-ray diffraction studies are difficult to perform due to twinned domains, and the various studies investigating the bond lengths between Fe+2 and Fe+3 at the octahedral sites have shown at most a charge disproportionality. However, the presence of a Bragg forbidden (001/2) superlattice peak, which is only observable in the insulating state at resonant energies, is a hidden door into magnetite’s charge and orbital states. We have used coherent soft x-rays at the Fe L-edge resonant energy to probe the orbital order at the octahedral Fe sites. An unexpected diffuse scattering ring about the (001/2) superlattice peak that exists in both the insulating and metallic phases was discovered simultaneously. By following the shape and intensity of this diffuse scattering ring in reciprocal space, we can map out the degree of correlated disorder of the Fe ions in both the metallic and insulating phases. |
Thursday, March 5, 2020 9:00AM - 9:12AM |
R50.00006: Metal-insulator transition with ferromagnetic background in the two-orbital model for manganites Cengiz Sen, Elbio Dagotto The complex spin, electron and phonon dynamics of manganese oxides continues to attract attention. In this talk, we present results of unbiased Monte Carlo simulations with fermionic exact diagonalization of the two-orbital model with Jahn-Teller phonons at filling x=1/3 on lattice sizes up to 15x15. We identify a region in the finite-temperature phase diagram with a metal-insulator transition upon increasing electron-phonon coupling. In the metal the spin background is ferromagnetic (FM) with uniform charge order, whereas the insulator shows diagonal stripes while retaining the FM background. We report resistivity and magnetization measurements alongside with spin and charge structure factors. |
Thursday, March 5, 2020 9:12AM - 9:24AM |
R50.00007: Gyrotropic birefringence via electromagnon resonance in multiferroic manganite Makiko Ogino, Yoshio Kaneko, Yoshinori Tokura, Youtarou Takahashi The magnetoelectric (ME) coupling has been exemplified in the certain classes of crystalline solids including multiferroics and topological insulators. Since the ME coupling modifies the Maxwell’s equations, such ME materials give rise to the exotic electromagnetic phenomena. In particular, the light-matter interaction can induce the unconventional gyrotropy, which is called gyrotropic birefringence (GB), whereas its observation remains highly limited. We focus on the electrically active spin excitation i.e. electromagnon, inherent to the multiferroics, which potentially exhibits the enhanced optical ME effect. Here we report the first observation of GB on multiferroic manganite with spin-induced ferroelectricity by use of the time-domain terahertz polarimetry. The enhanced optical rotation arising from the GB was found on the electromagnon resonance. It is demonstrated that the GB is scaled by the bilinear coupling of ferroic order parameters P・M (P: Electric polarization, M: magnetization) in the magnetic field dependence. In addition, the quantitative spectral analysis reveals that the electromagnon and antiferromagnetic resonance cooperatively produce the enhanced GB, indicating the important role of inter-mode coupling for the enhanced dynamical ME effect. |
Thursday, March 5, 2020 9:24AM - 9:36AM |
R50.00008: Torsional mode as order parameter in H-ErMnO3: mode screening, Fröhlich resonance, bipolarons Néstor Massa, Aurelien Canizarès, Leire del Campo, Karsten Holldack, Vinh Ta Phuoc, Paula Kayser, Jose Antonio Alonso While far infrared absorption, normal reflectivity, and emission spectra of hexagonal ErMnO3 give a quantitative picture of phonon softening and merging on heating, the torsional mode at ~306 cm-1 (300 K), associated to the negative thermal expansion and a c axis hybridization of O-2p with Er3+ levels, displays at lock-in Tc~830 K a distinctive infrared line shape anomaly and reststrahlen screening within the context of a ferroelectric instability inferred for a Mott-Hubbard insulator. Since the longitudinal optical (LO) mode macroscopic field screening implies phonon dynamic coupling to charge fluctuations in an electron correlated insulating polar environment we used the above the gap λexc= 355 nm Raman line to turn on the Fröhlich mechanism at macroscopic field frequencies at which the interaction between carriers and the Coulomb long range, responsible of the TO-LO split, takes place. We found a new Raman activated band that has its contour red shifted overlapping the infrared reflectivity minimum. It implies a univocal visualization of a huge electron-lattice interaction concomitant with finding small polaron correlations for which that phonon mediates in the formation of high temperature H-ErMnO3 mid-infrared bipolarons below the metal-insulator transition at ~1600 K. |
Thursday, March 5, 2020 9:36AM - 9:48AM |
R50.00009: Doping evolution of the electronic structure in RENiO3 Jiarui Li, Robert Green, Zhihai Zhu, Grace H Zhang, Da Zhou, Min Gu Kang, Jerzy T. Sadowski, Ronny Sutarto, Feizhou He, Zhen Zhang, Yifei Sun, Shriram Ramanathan, Riccardo Comin Rare earth nickelates (RENiO3) exhibit metal-insulator transitions accompanied by the appearance of charge and spin order, at times concurrently. The understanding of the evolving ground state in these materials is hindered by the existence of multiple competing orders which are further coupled to various kinds of local perturbations (strain, defects, disorder). Very recently, control of carrier doping by means of oxygen stoichiometry has been achieved in RENiO3, presenting an opportunity to study the broader electronic phase diagram of these systems. In this talk, I will present our recent soft X-ray spectroscopy, resonant scattering, and photoemission microscopy experiments on both pristine and electron doped RENiO3. Our results reveal the doping evolution of the electronic structure in RENiO3. |
Thursday, March 5, 2020 9:48AM - 10:00AM |
R50.00010: Local metallic properties of LaNiO3 detected using β-detected NMR Victoria Karner, Aris Chatzichristos, David L Cortie, Martin H Dehn, Oleksandr Foyevtsov, Kateryna Foyevtsova, Derek Fujimoto, Robert F Kiefl, Philip C. P. Levy, Ruohong Li, Ryan M. L. McFadden, Gerald Morris, Matt Pearson, Monika K Stachura, John Ticknor, Georg Christiani, Gennady Logvenov, Friederike Wrobel, Bernhard Keimer, Junjie Zhang, John Mitchell, W Andrew MacFarlane The rare earth nickelates (RNiO3) are a prototypical example of a metal-insulator transition in strongly correlated materials; LaNiO3 is the only RNiO3 that remains metallic . |
Thursday, March 5, 2020 10:00AM - 10:12AM |
R50.00011: Electron- and Hole-Doping Effects on the Metal-Insulator Transition in “113” Nickelates [RNiO3, R = Pr, Nd, (La,Y)] Prepared at High Oxygen Pressure* Gregorio Ponti, Zachary P. Kuklinski, Quinn D. B. Timmers, John Markert We report x-ray diffraction, electrical resistivity, and other data on bulk polycrystalline materials prepared under high oxygen pressure (150–200 bar) at high temperature (T ≈ 1000°C). These conditions stabilize the nearly simple-perovskite “113” structure, RNiO3. For the orthorhombic parent compounds with the largest rare-earth ions that exhibit a metal-insulator transition, R = Pr and Nd, we dope with divalent Sr and Ba (hole doping) and tetravalent Ce and Th (electron doping). Results for Nd1–xAxNiO3 (A= Sr, Ce, Th) have been reported previously1: for example, for Ce4+, the net effect on the metal-insulator transition, ∂TMI/∂x ≈ –220 K, was corrected for size effects to obtain a bare electron-doping effect, ∂TMI/∂xelec ≈ –1100 K. Remarkably in our study, we find that, for Pr1–xCexNiO3, the shift in the metal-insulator transition temperature with concentration x is positive, with a net ∂TMI/∂x ≈ +225 K. Also, we find hysteresis in the metallic resistivity of rhombohedral La1–xCexNiO3, perhaps a signature of low-T pseudogap monoclinic short-range order.2 |
Thursday, March 5, 2020 10:12AM - 10:24AM |
R50.00012: Large magnetic excitation gap in antiferromagnetic YNiO3 detected by NMR Lukas Korosec, Dariusz Gawryluk, Marisa Medarde, Toni Shiroka, Hans Rudolf Ott, Joel Mesot The rare-earth nickelate perovskites (RENiO3) are an archetypal family of strongly correlated electron materials. Their antiferromagnetic state with four nickel atoms per period remains poorly studied, even though it has been predicted to be a type-II multiferroic with large polarization. Currently, there is no agreement on the magnetic structure and low-energy spin model for bulk RENiO3. We present 17O nuclear-spin–lattice relaxation measurements demonstrating the presence of a large gap of 30 meV in the magnetic excitation spectrum of YNiO3. |
Thursday, March 5, 2020 10:24AM - 10:36AM |
R50.00013: Impact of low-temperature stripe freezing in La1.67Sr0.33NiO4 John Tranquada, Adrian Merritt, Dmitry Reznik, Vasile O Garlea, Genda Gu La1.67Sr0.33NiO4 develops charge stripe order below 240 K and spin stripe order below 190 K. We have reconsidered a wide variety of experimental studies that indicate changes in the stripe correlations below ~ 50 K [1]. From new neutron diffraction measurements of a significant set of stripe-order peaks, we make the case that the charge stripes, which can be centered on either Ni or O sites, become predominantly Ni-centered at low temperature. This is a prerequisite for the one-dimensional spin fluctuations on charge stripes that are observed at low temperature. |
Thursday, March 5, 2020 10:36AM - 10:48AM |
R50.00014: Many-body physics of single and double spin-flip excitations in NiO Abhishek Nag, Hannah Robarts, F Wenzel, Jiemin Li, H. Elnaggar, Ru-Pan Wang, A C Walters, Mirian Garcia-Fernandez, F. M. F. de Groot, Maurits Haverkort, Kejin Zhou Understanding many-body physics of elementary excitations has advanced our control over material properties. Here, we study spin-flip excitations in NiO using Ni L3-edge RIXS and present a strikingly different resonant energy behaviour between single and double spin-flip excitations. Comparing our results with single-site full-multiplet ligand field theory calculations we find that the spectral weight of the double-magnon excitations originates primarily from the double spin-flip transition of the quadrupolar RIXS process within a single magnetic site. Quadrupolar spin-flip processes are among the least studied excitations, despite being important for multiferroic or spin-nematic materials due to their diffi�cult detection. We identify intermediate state multiplets and intra-atomic core-valence exchange interactions as the key many-body factors determining the fate of such excitations. |
Thursday, March 5, 2020 10:48AM - 11:00AM |
R50.00015: Structural and electronic properties of doped NiO Friederike Wrobel, Changhee Sohn, Hyowon Park, Hyeondeok Shin, Ho Nyung Lee, George E Sterbinsky, Haw-Wen Hsiao, Jian-Min Zuo, Panchapakesan Ganesh, Jaron Krogel, Anouar Benali, Paul Kent, Olle Heinonen, Anand Bhattacharya How the electronic structure of correlated oxides evolves with electron and hole doping is a fundamental question of importance for applications. We have studied structural and electronic properties of high-quality MBE-grown doped NiO thin films using a variety of experimental and theoretical methods. We find that both K- and In-doped films at concentrations below 10% exhibit good X-ray diffraction spectra. However, extended X-ray absorption fine structure (XAFS) spectra indicate broadening of the K-O bond length distribution, and an increased bond length, much larger than obtained using theoretical methods. Ab-initio molecular dynamics suggests the XAFS feature is due to K-Ov-K defect structures in the thin film. Spectroscopic ellipsometry shows a smooth but asymmetric evolution of a decreasing optical gap for hole (K) and electron (In) doping, consistent with the behavior of a charge transfer insulator. Analysis shows that the decrease of the optical gap is due to the emergence of an absorption peak below (in energy) the optical gap of un-doped NiO. Calculations using Dynamical Mean Free Theory are in good agreement with the measurements and show the emergence of occupied states just above the valence band edge, and with an asymmetry between hole and electron doping. |
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