Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session Y43: Bulk OxidesFocus
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Sponsoring Units: GMAG DMP DCOMP Chair: Antia Botana, Argonne Natl Lab Room: 390 |
Friday, March 17, 2017 11:15AM - 11:27AM |
Y43.00001: Electron doping of SmNiO$_3$ from first principles Michele Kotiuga, Karin M. Rabe Rare earth nickelates have rich phase diagrams involving charge, orbital and magnetic order. In past experimental work, doping SmNiO$_3$ with interstitial hydrogen at room temperature has resulted in a new insulating state, characterized by a large change in the resistivity [1]. In this work we use the first-principles density functional theory (DFT) + U method to study the effect of added electrons on the crystal and electronic structure of SmNiO$_3$. We consider added electron concentrations of $\frac{1}{4}$, $\frac{1}{2}$, $\frac{3}{4}$ and 1 electron per Ni, starting from various low energy structures of pure SmNiO$_3$, which include either an oxygen-octahedron shape distortion or a breathing distortion characteristic of disproportionation. We analyze the changes in the local crystal and electronic structure and magnetic ordering, and relate the changes to the changes in optical and transport properties observed experimentally. $\newline$ [1] J. Shi, Y. Zhou, S. Ramanathan, Nat Comm 5, 4860 (2014) [Preview Abstract] |
Friday, March 17, 2017 11:27AM - 11:39AM |
Y43.00002: Mimicking cuprates: large orbital polarization in square-planar nickelates. Junjie Zhang, A.S. Botana, John W. Freeland, D. Phelan, Hong Zheng, V. Pardo, M. R. Norman, John Mitchell High temperature cuprate superconductivity remains a defining problem in condensed matter physics. Among myriad approaches to addressing this problem has been the study of alternative transition metal oxides with similar structures and 3d electron count that are suggested as proxies for cuprate physics. Here, we report one such alternative: the low-valent, quasi-two-dimensional trilayer nickelates, R4Ni3O8 (R$=$La and Pr). By combining x-ray absorption spectroscopy and density functional theory calculations, we find that these compounds exhibit a low-spin configuration and significant orbital polarization of the occupied eg states with pronounced dx2-y2 character near the Fermi energy. Notably, a charge-ordered stripe phase, previously reported for La4Ni3O8, collapses in favor of a metallic ground state when substituting La with Pr, offering entr\'{e}e to a region of 3d electron count important to hole-doped high-Tc cuprates but in the absence of quenched disorder. [Preview Abstract] |
Friday, March 17, 2017 11:39AM - 11:51AM |
Y43.00003: Charge stripes, nematicity and disorder in a cuprate superconductor Damjan Pelc, Marija Vu\v{c}kovi\'{c}, Hans-Joachim Grafe, Seung-Ho Baek, Miroslav Po\v{z}ek Charge stripe order is recognized as an important ingredient of the physics of cuprates, yet the thermodynamics of its formation and the influence of disorder are unclear. We present a study of the development of charge stripes in the cuprate La$_{1.8−x}$Eu$_{0.2}$Sr$_x$CuO$_4$, using three complementary experimental techniques: nuclear quadrupole resonance, nonlinear conductivity and specific heat\footnote{D. Pelc et al., \textit{Nature Comm.} \textbf{7}, 12775 (2016)}. We find an intermediate phase between (pseudogapped) metal and charge stripes, existing in a dome-shaped region of the phase diagram and appearing through a sharp phase transition. A novel technique\footnote{M. Do\v{s}li\'{c}, D. Pelc, M. Po\'{z}ek, \textit{Rev. Sci. Instr.} \textbf{85}, 073905 (2014)} is used for measurements of nonlinear response, which show that the new phase is consistent with a charge nematic. This is in agreement with recent predictions of charge stripe formation with quenched disorder\footnote{L. Nie, G. Tarjus, S. Kivelson, \textit{Proc. Nat. Acad. Sci. USA} \textbf{111}, 7980 (2014)}. Our experiments thus resolve the intricate process of charge stripe formation and provide a link to other materials with electronic nematic order. [Preview Abstract] |
Friday, March 17, 2017 11:51AM - 12:03PM |
Y43.00004: Orbital ordering induced metal-insulator transition in rhenium based double perovskites Alex Lee, Chris Marianetti Double perovskites (DPs), which are transition metal oxides with two types of transition metals, offer a huge phase space of possibilities and the potential for novel physics. More specifically, Re-based DPs $A_2B$ReO$_6$ ($A$=Sr,Ca and $B$=Cr,Fe) show interesting insulator to metal transitions (MIT) as a function of temperature. Here we systematically study the electronic properties and MIT of the Re-based DPs using density functional theory + $U$ and dynamical mean-field theory (DMFT) calculations. We show that the on-site interaction $U$ for Re is necessary for obtaining the experimentally observed insulating state in Sr$_2$CrReO$_6$, Ca$_2$CrReO$_6$, and Ca$_2$FeReO$_6$, primarily via the induction of antiferro orbital ordering on the Re sites. This orbital ordering is enhanced by cooperating with local octahedral distortions and tilting. Our predicted insulating ground state of Sr$_2$CrReO$_6$ is consistent with recent experiments. The experimentally observed MIT at 140K in Ca$_2$FeReO$_6$, is elucidated by using the experimental structures just below and above the phase transition. We find that Sr$_2$FeReO$_6$ remains metallic, yielding a qualitatively consistent description of this entire family. Specific comparisons will be made between DFT+U and DFT+DMFT calculations. [Preview Abstract] |
Friday, March 17, 2017 12:03PM - 12:15PM |
Y43.00005: Spin wave resonances and optical activity in simple chromites RCrO$_{\mathrm{3}}$ (R$=$Pr, Sm, Er) at ultralow temperatures in the THz region N. E. Massa, K. Holldack, R. Sopracase, V. Ta Phuoc, D. De Sousa Meneses, L. del Campo, P. Echegut, J. A. Alonso We show that the spin reorientation temperature T$_{\mathrm{SR\thinspace }}$in polycrystalline RCrO$_{\mathrm{3}}$ (R$=$Pr, Sm, Er) is determinant on spin wave resonances,$^{\mathrm{1}}$ ferromagnetic-like (FM) and antiferromagnetic-like (AFM), being optically active. We also report on crystal field temperature and field dependences. Pr$^{\mathrm{3+}}$ non-Kramers lowest energy main transition emerges at 100 K. The no detection of spin wave resonances is attributed to Pr$^{\mathrm{3+}}$ remaining paramagnetic disrupting Cr$^{\mathrm{3+}}$-Pr$^{\mathrm{3+\thinspace }}$exchanges. In SmCrO$_{\mathrm{3\thinspace }}$we propose magnetic compensation for not detecting Sm$^{\mathrm{3+\thinspace }}$ground state transitions. The FM and AFM harden upon lowering temperature and split linearly on applied fields at 5 K. In ErCrO$_{\mathrm{3}}$ the Er$^{\mathrm{3+}}$ Kramers doublet becomes active at \textasciitilde T$_{\mathrm{SR}}$ onset. Each Zeeman line splits further under magnetic fields. The field-induced spin reversal at \textasciitilde 1.5 T yields a secondary split at the highest Zeeman level. The $\Gamma_{\mathrm{2}}$ 5 K resonances show concerted frequency-intensity temperature dependence. A shoulder in the AFM profile points to subtle distortions by Er$^{\mathrm{3+}}$ smaller ion size. Both modes merge into an induced continuum prompted by the external field. At 2 K, in the $\Gamma _{\mathrm{1}}$ representation, the resonances reduce to one excitation. [1] F. Keffer and C. Kittel. Phys. Rev. \textbf{85}, 329 (1952); G. F. Herrmann. Phys. Rev. \textbf{133}, A1334 (1964). [Preview Abstract] |
Friday, March 17, 2017 12:15PM - 12:27PM |
Y43.00006: Revising the magnetic structure and dynamics of Yttrium Iron Garnet Andrew Princep, Andrew Boothroyd, Russell Ewings, Simon Ward, Carsten Dubs Yttrium iron garnet (YIG) is the `miracle material' of microwave magnetics. Since its synthesis by Geller and Gilleo in 1957, it is widely acknowledged to have contributed more to the understanding of electronic spin-wave and magnon dynamics than any other substance. Its astonishingly narrow excitation linewidth allows magnon propagation to be observed over centimetre distances, making it both a superior model system for the experimental study of fundamental aspects of microwave magnetic dynamics and an ideal platform for the development of microwave magnetic technologies. Our experiments on a large, pristine single crystal at the ISIS facility using both diffraction and time-of-flight spectroscopy have provided new results on both the magnetic structure and the excitation spectrum, which revise nearly 60 years of scientific research and will be essential insights for the fledgling scientific field of Magnonics. [Preview Abstract] |
Friday, March 17, 2017 12:27PM - 12:39PM |
Y43.00007: Low energy spin dynamics of rare-earth orthoferrites YFeO$_{\mathrm{3}}$ and LaFeO$_{\mathrm{3}}$ Kisoo Park, Hasung Sim, Jonathan Leiner, Yoshiyuki Yoshida, Hiroshi Eisaki, Shinichiro Yano, Jason Gardner, Je-Geun Park YFeO$_{\mathrm{3}}$ and LaFeO$_{\mathrm{3\thinspace }}$are members of the rare-earth orthoferrites (RFeO$_{\mathrm{3}})$ family with \textit{Pbnm} space group. With the strong superexchange interaction between Fe3$+$ ions, both compounds exhibit the room temperature antiferromagnetic order (T$_{\mathrm{N}}$ \textgreater 600 K) with a slight spin canting. Here we report low-energy magnetic excitation of YFeO$_{\mathrm{3}}$ and LaFeO$_{\mathrm{3}}$ using inelastic neutron scattering measurements, showing evidence of magnon mode splitting and a spin anisotropy gap at the zone center. Spin wave calculations with the spin Hamiltonian including both Dzyaloshinsky-Moriya interaction and single-ion anisotropy accounts for the observed features well. Our results offer insight into the underlying physics of other RFeO$_{\mathrm{3\thinspace }}$with magnetic rare-earth ions or related Fe$^{\mathrm{3+}}$-based multiferroic perovskites such as BiFeO$_{\mathrm{3}}$. [Preview Abstract] |
Friday, March 17, 2017 12:39PM - 12:51PM |
Y43.00008: Growth of EuO Single Crystals at Reduced Temperatures Tiglet Besara, Daniel Ramirez, Jeffrey Whalen, Theo Siegrist Single crystals of Eu$_{1-x}$Ba$_{x}$O have been grown in a barium-magnesium flux at moderate temperatures up to 1000$^{\circ}$C, producing single crystals with barium doping levels ranging from $x=0.03$ to $x=0.25$. Magnetic measurements show that the ferromagnetic Curie temperature $T_{C}$ correlates with the Ba doping levels, and a modified Heisenberg model is employed to describe the $T_{C}$ dependence on the stoichiometry. The decrease in $T_{C}$ is dominated by the Ba substitution on the Eu lattice with a small contribution arising from the lattice strain. Extrapolation of results indicates that a sample at $x=0.72$ should have a $T_{C}=0$ K, potentially producing a quantum phase transition in this material.\\ \\ This work was supported by the Department of Energy, Office of Basic Science, under contract DOE SC-0008832. This work has been performed at the National High Magnetic Field Laboratory, which is supported by the National Science Foundation Cooperative Agreement DMR-1157490, the State of Florida, and the U.S. Department of Energy. [Preview Abstract] |
Friday, March 17, 2017 12:51PM - 1:03PM |
Y43.00009: Exchange Splitting above the Curie Temperature in EuO Timm Gerber, Markus Eschbach, Tristan Heider, Ewa Mlynczak, Patrick Loemker, Pika Gospodaric, Mathias Gehlmann, Moritz Ploetzing, Okan Koeksal, Rossitza Pentcheva, Lukasz Plucinski, Claus M. Schneider, Martina Mueller The ferromagnetic semiconductor europium monoxide (EuO) is an attractive material for fundamental research in the field of spintronics [1,2]. The magnetism in EuO is usually explained in the Heisenberg model of localized spins and their exchange interactions. While the material is known since decades, the actual exchange mechanisms are still debated [3]. Here, the electronic structure of EuO is investigated by means of spin- and angle-resolved photoemission spectroscopy (spinARPES). Our spin-resolved data reveals a complex temperature dependence of the occupied density of states which could not be accessed by previous spin-integrated measurements [4]. We find that the exchange splitting of the O 2p band is present also above the Curie temperature. Our findings are explained by the presence of co-called ’spin-blocks’ (i.e. large clusters of spontaneously magnetized material) that are present at the Curie temperature, and even above. [1] M. Mueller et. al., J. Appl. Phys. 105, 07C917 (2009) [2] A. Schmehl et. al., Nat. Mater. 6, 882 (2007) [3] X. Wan et. al., Phys. Rev. B, 83, 205201 (2011) [4] H. Miyazaki et. al., Phys. Rev. Lett. 102, 227203 (2009) [Preview Abstract] |
Friday, March 17, 2017 1:03PM - 1:15PM |
Y43.00010: Quantum Monte Carlo study of a K-doped NiO Mott insulator Anouar Benali, Hyeondeok Shin, Ye Luo, Jaron Krogel, Panchapakesan Ganesh, Janakiraman Balachandran, Paul Kent, Olle Heinonen Doped Mott insulators are of particular interest in thin film magnetic heterostructures and high temperature superconductivity. Due to the strong contribution of electronic correlations in such systems, traditional electronic structure methods fail to predict or even just reproduce their properties. Since the late 40s, NiO was intensively studied as a prototypical Mott insulator. However, most of the theoretical studies depending on Density Functional Theory failed to reproduce all of NiO properties and were unable to predict the properties of the system in the presence of defects. Quantum Monte Carlo (QMC) is a many-body quantum theory solving explicitly the electronic correlations, allowing reproducing and predicting materials’ properties with a limited number of controlled approximations. In this study, we investigate the energetics and properties of a pure bulk phase NiO and K-doped NiO semiconductor using QMC. Our results are then compared to a wide range of DFT approximations including SIC-DFT, DFT+U, hybrid-DFT. [Preview Abstract] |
Friday, March 17, 2017 1:15PM - 1:27PM |
Y43.00011: DFT with larger supercells explains the band gap formation in the antiferromagnetic and paramagnetic phases of the Mott insulators MnO, FeO, CoO, and NiO Alex Zunger, Giancarlo Trimarchi The existence of large band gaps both in the antiferromagnetic (AFM) and the paramagnetic (PM) phases of the classic Mott insulators MnO, FeO, CoO, and NiO has traditionally been discussed in terms of theoretical methods requiring both (i) simple (often primitive) unit cells and (ii) correlated-electron methodologies. We show that if condition (i) is avoided (by using supercells, such as PM special quasi-random structures, in which chemically identical atoms can have different local environments), then even without condition (ii) one can describe the gaps and moments within a single-determinant DFT band structure approach. In this approach gapping is caused by basic structure, magnetism, and bonding effects underlying DFT, not via dynamic correlation (absent from DFT). As long as correlation is simplistically considered as ``anything that DFT does not get right'', gap formation in the AFM and PM phases is not due to correlation. This result defines the minimal theoretical methods needed to explain gapping and points to the possibility that some transition-metal oxides generally considered to have localized electrons detrimental to transport, could, in fact, rejoin the family of electronic semiconductors, to the benefit of a carrier transport technologies. [Preview Abstract] |
Friday, March 17, 2017 1:27PM - 1:39PM |
Y43.00012: Ultrafast electron dynamics in MnO: a non-adiabatic TDDFT+DMFT study Shree Ram Acharya, Volodymyr Turkowski, Talat S. Rahman We have examined the ultrafast electron dynamics in the insulating antiferromagnet MnO when perturbed by a laser pulse. To take properly into account the effects of electron correlations, we have used our newly proposed ab initio approach in which we combine the benefits of Time-Dependent Density-Functional Theory and Dynamical Mean-Field Theory (TDDFT+DMFT) [1]: the TDDFT equations are solved by using the exchange correlation potential obtained from the DMFT solution of an effective Hubbard model. Consequent analysis of the excitation spectrum of the system demonstrates the existence of bound excitonic states with rather strong binding energy of order 100meV. Furthermore, details of the ultrafast charge dynamics allowed us to identify the main channels of the charge response, dominated by the inter-orbital d-electron transitions. We find that strong time-resolved electron-electron interactions play an important role in the response of MnO to a short laser pulse. Good agreement of our result with available experimental data [2] attests to the validity of this TDDFT+DMFT method for understanding electron relaxation dynamics in strongly correlated systems such as MnO. [1] S.R. Acharya et al., Computation 4, 34 (2016); [2] J. Nishitani et al., Phys. Stat. Sol. C 13, 113 (2016). [Preview Abstract] |
Friday, March 17, 2017 1:39PM - 1:51PM |
Y43.00013: Determination of the Magnetic Structure of Complex \textit{anti-}Perovskite Fluorides by Neutron Diffraction Justin Felder, Jeongho Yeon, Hans-Conrad zur Loye An unusual family of anti-perovskite fluorides consisting of complex ions as the A, B, and X building units has been synthesized as single crystals. This family of anti-perovskites provides a unique framework to probe the magnetic properties of transition metals. Presented here is the Fe endmember of the family: [Cu(H$_{\mathrm{2}}$O)$_{\mathrm{4}}$]$_{\mathrm{3}}$[FeF$_{\mathrm{6}}$]$_{\mathrm{2}}$. The iron member exhibits complex magnetic behavior at low temperatures, which has been probed by magnetometry and neutron diffraction experiments. Presented here are the results from the anisotropic magnetometry study as well as the magnetic spin structure as determined by neutron diffraction experiments. The materials presented here represent an interesting class of perovskites that are as-yet unexplored. Given the wide range of properties possible in perovskites and related structures, it is reasonable to expect that further exploration of these materials will reveal many interesting attributes; both chemical and physical. [Preview Abstract] |
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