Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P46: Unconventional Order and Phase Behaviors in Complex OxidesFocus
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Sponsoring Units: GMAG DMP DCOMP Chair: Arun Paramekanti, Univ of Toronto Room: 708 |
Wednesday, March 4, 2020 2:30PM - 3:06PM |
P46.00001: Collective Spin and Charge 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 into superconductors. |
Wednesday, March 4, 2020 3:06PM - 3:18PM |
P46.00002: An ab initio study of electron-hole pairs in the insulating single layer cuprates and nickelates Christopher Lane, Jian-Xin Zhu Advanced density functionals have proven to be an indispensable tool in studying correlated materials exhibiting the delicate interplay between complex charge and non-collinear magnetic order. We perform a comparison study of the electronic and magnetic structure of a prototypical high-temperature superconductor La2CuO4 with the isostructural single-layer nickelate La2NiO4. We find key differences in the low-energy electronic structure, where in particular, La2NiO4 exhibits an enhanced Hund's coupling. Additionally, utilizing our accurate ab initio ground state, we obtain the excitonic dispersion for each material. Excitons in La2CuO4 are delocalized and can freely move in the CuO2 plane without disturbing the antiferromagnetic order. In contrast, in La2NiO4 we find the low-lying excitonic states to be extremely localized, producing a nearly flat dispersion. Our results are in excellent agreement with RIXS observations, and give insights into the excited state dynamics of the cuprates and nickelates. Finally, we will briefly connect our results to the newly discovered superconducting infinite-layer nickelates. |
Wednesday, March 4, 2020 3:18PM - 3:30PM |
P46.00003: Low Temperature Specific Heat of Doped SrTiO3: Doping Dependence of the Effective Mass and Kadowaki-Woods Scaling Violation Eric McCalla, Maria Navarro Gastiasoro, Guy Cassuto, Rafael Fernandes, Chris Leighton We discuss wide-doping-range (8 x 1017 to 4 x 1020 cm-3 Hall electron density) low temperature specific heat measurements on single crystal SrTiO3:Nb, correlated with electronic transport data and tight-binding modeling [1]. Lattice dynamic contributions to specific heat are shown to be well understood, albeit with unusual sensitivity to doping, likely related to soft modes. Electronic contributions to specific heat provide effective masses that increase substantially, from 1.8 to 4.8me, across the two SrTiO3 Lifshitz transitions. It is shown that this behavior can be quantitatively reconciled with quantum oscillation data and calculated band structure, establishing a doping-independent mass enhancement factor of 2.0. With the doping-dependent T2 resistivity prefactor and Sommerfeld coefficient known, Kadowaki-Woods scaling has been tested over the entire doping range. Despite Fermi liquid behavior in electronic specific heat, standard Kadowaki-Woods scaling is dramatically violated, highlighting the need for new theoretical descriptions of T2 resistivity in SrTiO3. |
Wednesday, March 4, 2020 3:30PM - 3:42PM |
P46.00004: Influence of structural distortions on the magnetic order of rare-earth titanates Ana Najev, Damjan Pelc, Sajna Hameed, Joseph Joe, Martin Greven, Miroslav Pozek Perovskite oxides feature fundamentally and technologically alluring properties such as magnetism, superconductivity and colossal magnetoresistance. How structural distortions and disorder influence the electron system in these materials is an important open question. Rare-earth titanates show promise in shedding new light on this problem through the study of their magnetic ground states, which are controlled by distortions induced by different-sized rare-earth ions. The compounds exhibit an interplay among charge, orbital, spin and lattice degrees of freedom, which produces a complex phase diagram that includes ferromagnetic and antiferromagnetic phases (e.g., in Y1-xLaxTiO3) and metal-insulator transitions (e.g., Y1-xCaxTiO3, La1-xSrxTiO3). We have conducted NMR measurements on select rare-earth titanates. Our results point to unusual local behavior well above magnetic ordering temperatures, which is not seen by macroscopic probes. Additionally, we have modified the structural distortions by uniaxial pressure and investigated their effect via magnetic susceptibility measurements. |
Wednesday, March 4, 2020 3:42PM - 3:54PM |
P46.00005: Changes in phonon dispersion across metal-insulator transition in a Pr-containing cobaltite Daniel Phelan, Matthew Krogstad, Nathaniel Schreiber, Raymond Osborn, Ayman Said, Hong Zheng, Stephan Rosenkranz A group of praseodymium-containing cobaltites are known to undergo 1st order metal-insulator transitions that are correlated to valence shifts that involve both Pr and Co cations. We have measured the dispersion of acoustic phonons in a single crystal of (Pr0.85Y0.15)0.7Ca0.3CoO3-δ in both the metallic and insulating states and have observed differences which arise at the phase transition temperature. We interpret changes in the mode energies in terms of changes in the elastic constants. Anomalous damping of the phonons is observed near the phase transition. Elastic diffuse scattering, symptomatic of precursory behavior in the metallic phase is observed. |
Wednesday, March 4, 2020 3:54PM - 4:06PM |
P46.00006: Phonon density of states of the infinite layer nickelate Nd0.8Sr0.2NiO2 Stephan Rosenkranz, Daniel Phelan, Bixia Wang, Hong Zheng, Douglas L Abernathy, John Mitchell, Raymond Osborn One of the main mysteries of high-temperature superconductivity in oxides is why this has so far only been observed for cuprates, but not for other oxides with transition metals exhibiting similar electronic properties. The recent report of superconductivity up to 15K in a thin film nickelate with similar crystal and electronic structures to that of the cuprates, suggests that these infinite-layer nickelates could harbor superconductivity with the same underlying pairing mechanism as the cuprates. Here we report inelastic neutron scattering measurements performed on a bulk sample of Nd0.8Sr0.2NiO2, the same nominal composition for which superconductivity was observed in thin film form grown on a SrTiO3 substrate. We will discuss the implications of our results, in particular the measured phonon density of states, on possible superconducting mechanisms in this compound. |
Wednesday, March 4, 2020 4:06PM - 4:18PM |
P46.00007: Study of competing order parameters and relaxation dynamics in La1/3Sr2/3FeO3 using first-principles Nam Nguyen, Vijay Singh, Hyowon Park La1/3Sr2/3FeO3 is a strongly correlated material exhibiting the strong interplay between spin, charge, and lattice degrees of freedom. It is an antiferromagnetic Mott insulator at low temperature below 200K accompanying a charge ordering with the Fe-O bond disproportionation. The charge ordering driven by magnetism shows the Fe3+/Fe5+/Fe3+/Fe3+/Fe5+/Fe3+ structure along the [111] direction, and it disappears above 200K as the magnetic order is suppressed. Using first-principles calculations, we identify two charge ordering structures can occur in this material. With close energetics near the ground state and study electronic and structural orders along the energy path obtained using method of climbing image nudged elastic band. We then solve the time-dependent Landau equation along the Free energy path and study the non-equilibrium dynamics of those competing order parameters. Our results can provide an insightful explanation to the slow dynamics of this material observed in the recent ultra-fast experimental measurement. |
Wednesday, March 4, 2020 4:18PM - 4:30PM |
P46.00008: Synthesis and characterization of bulk polycrystalline Nd1-xSrxNiO3 and Nd1-xSrxNiO2 Bixia Wang, Hong Zheng, Stephan Rosenkranz, Daniel Phelan, John Mitchell Recently, superconductivity has been reported for Sr-doped nickelate NdNiO2 thin films [1]. This intriguing result represents a realization of the long-sought superconductivity in oxides that possess low-valence nickel cations in square planar coordination. In this work, we have synthesized bulk polycrystalline Nd1-xSrxNiO3 and Nd1-xSrxNiO2 compounds. The electrical, magnetic and structural properties of these compounds are discussed. |
Wednesday, March 4, 2020 4:30PM - 4:42PM |
P46.00009: Quantum Materials for Energy Efficient Neuromorphic Computing: Defective La1-xSrxCoO3-d Shenli Zhang, Giulia Galli We present a first principle study of La1-xSrxCoO3-d, a promising candidate material to build devices for neuromorphic computers. In particular we investigate how the generation of oxygen vacancies can drive a metal-to-insulator transition in the system, with focus on the interplay between structural, electronic and magnetic properties. |
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P46.00010: Protonation-induced magnetic phase transition in SrRuO3 Weidong Luo, Zijun Tian, Zhuolu Li, Shengchun Shen, Pu Yu In transition metal oxides, the subtle modulation of charge carrier triggers the emergence of exotic electronic and magnetic properties. In the ferromagnetic metal SrRuO3, experiment has shown a systematic and reversible control of both carrier density and crystalline symmetry through the ionic liquid gating induced protonation. The insertion of protons dopes the SrRuO3, leading to a ferromagnetic to paramagnetic phase transition. In order to understand the protonation induced structural and magnetic phase transformations in SrRuO3, we performed first-principles calculations. The proton intercalation leads to a significant splitting of the degenerated Ru t2g bands, resulting in dramatically modified density of states. The lattice also shows a significant expansion with the intercalation of proton, consistent with the XRD results. The observed ferromagnetic to paramagnetic transition in SrRuO3 can be understood within the Stoner model. |
Wednesday, March 4, 2020 4:42PM - 5:18PM |
P46.00011: Magnetic field effect and superconductivity in multipolar order Invited Speaker: SungBin Lee Exotic multipolar degrees of freedom have been issued in many context of heavy fermions and other correlated systems. Despite their existence, however, detection of such multipolar ordering still remains controversy. Furthermore, there are few studies on interesting correlation phenomena due to multipolar Kondo effect. In this talk, focusing on Pr based cage compounds, we first discuss the magnetic field effect of multipolar order and suggest unique way to probe multipolar order based on magnetostriction experiment. Then, we also explore multipolar Kondo effect in Pr based semimetals and study realization of topological superconductivity controlled via multipolar degrees of freedom. |
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