Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session H23: Excitations in Magnetic Oxides (Bulk)Focus
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Sponsoring Units: GMAG DMP DCOMP Chair: Huibo Cao, Oak Ridge National Lab Room: LACC 402B |
Tuesday, March 6, 2018 2:30PM - 2:42PM |
H23.00001: Magnetic excitations of the frustrated ferromagnetic chain LiCuSbO4 Luwei Ge, Martin Mourigal J1 - J2 one-dimensional frustrated spin-1/2 chains with ferromagnetic J1 are believed to host novel states such as vector chiral orders, spin nematic states and spin density wave states. Especially the competition between spin nematic states and spin density wave states in external magnetic field has been drawing much attention. With a feasible saturation field Hsat ~ 12 T, LiCuSbO4 serves as a good experimental candidate. Recent NMR and μSR studies have found evidence for a multipolar nematic phase at certain field range. In our work, we measured detailed ineslatic neutron scattering spectra on powder sample at low temperature in various magnetic fields. The results, along with recent theoretical studies, help us narrow down the detailed Hamiltonian and explore the possible phases in the system, in particular, in light of possible dimerization of the J1 exchange. |
Tuesday, March 6, 2018 2:42PM - 2:54PM |
H23.00002: Collective Excitations in the Frustrated Classical Spin Liquid MgCr2O4 XIAOJIAN BAI, Eliot Kapit, Joseph Paddison, Jiajia Wen, Seyed Koohpayeh, Garrett Granroth, Alexander Kolesnikov, Tyrel McQueen, John Chalker, Collin Broholm, Martin Mourigal Frustrated magnetic materials are of fundamental interest because they show exotic properties that arise from competing constraints; e.g., suppression of conventional magnetic order and sensitivity of the ground state to perturbations. The spinel MgCr2O4 is a canonical example of a highly-frustrated antiferromagnet in which Heisenberg spins occupy a pyrochlore lattice of corner-sharing tetrahedra. Magnetic frustration is demonstrated by the suppression of the magnetic ordering temperature compared to the Weiss constant and broad magnetic excitations resembling emergent hexagonal spin-loops. We present a comprehensive single crystal inelastic neutron scattering study of this material in the spin liquid regime based on a classical Heisenberg model. The dynamical structure factor is simulated in the framework of spin-wave theory and shows excellent agreement with the experimental data. |
Tuesday, March 6, 2018 2:54PM - 3:06PM |
H23.00003: Observation of spin and charge stripe correlations in La2-x-yEuySrxCuO4 Alexander Zakrzewski, Thomas Johnson, Alexandra Cote, Sangjun Lee, Gilberto De La Pena, Derick Gonzalez-Acevedo, Songxue Chi, Peter Abbamonte, Greg MacDougall The role of co-existing spin and charge (‘stripe’) orders in the La-based 214 cuprate superconductors has been a topic of enduring interest, and one with renewed relevance. Often presented as a prototypical stripe material, the family La2-x-yEuySrxCuO4 (LESCO) has been explored far less than other stripe candidates, with spin correlations almost completely unstudied to date. In this talk, we will present the results of our recent neutron and soft x-ray scattering studies of single crystals of LESCO grown at Illinois. These data imply the existence of parallel stripe order near 1/8 Sr-doping below critical temperatures TSO = 40K and TCO = 80K for spin and charge correlations, respectively. We will further discuss the measured temperature and Sr-doping dependence, as well as recent bulk magnetization measurements which reveal a strongly anisotropic Meissner response consistent with the decoupling of superconductivity between CuO2 planes. The collective results will be discussed in the context of pair-density-wave theories and the coupling between superconductivity and alternate orders in the cuprates. |
Tuesday, March 6, 2018 3:06PM - 3:18PM |
H23.00004: Terahertz excitation of magnon modes in CaFe$_2$O$_4$ Thuc Mai, Lunyong Zhang, Sang-Wook Cheong, Rolando Valdes Aguilar We report on the q=0 magnetic excitations in the orthorhombic antiferromagnet CaFe$_2$O$_4$, using time-domain terahertz spectroscopy. Multiple excitations were observed, with different selection rules. The temperature dependence of these excitations reveals their magnetic origin. Interestingly, we find that the gap excitation is split into two of slightly different energies for two different THz polarizations. This suggests that there are two easy-plane single ion anisotropy energies that split the gap at the magnetic zone center. We can explain the different excitation energies and their selection rules using classical spin wave theory. |
Tuesday, March 6, 2018 3:18PM - 3:30PM |
H23.00005: Magnetic excitations in bulk multiferroic two-dimensional triangular lattice antiferromagnet (Lu,Sc)FeO3 Jonathan Leiner, Taehun Kim, Kisoo Park, Joosung Oh, Toby Perring, Helen Walker, Xianghan Xu, Sang-Wook Cheong, Je-Guen Park Non-collinear two-dimensional triangular antiferromagnets (2D TLAF) are currently an area of much active research due to their unique magnetic properties, which lead to non-trivial quantum effects that experimentally manifest themselves in the spin excitation spectra. Recent examples of such insulating 2D TLAF include (Y,Lu)MnO3 and CuCrO2. LuFeO3 is a recently discovered multiferroic material, which is isostructural to LuMnO3 and contains one more electron in the eg manifold. Characterization of the AFM ground state (TN = 155 K) in LuFeO3 thin films with magnetometry and neutron diffraction has been previously reported. We present the first report of the spin dynamics in a bulk single crystal of (Lu0.6Sc0.4)FeO3 measured via time-of-flight inelastic neutron scattering, and compare and contrast these results with those found in LuMnO3. |
Tuesday, March 6, 2018 3:30PM - 3:42PM |
H23.00006: Solitary magnons and orphaned spins in the S=5/2 antiferromagnet CaFe2O4 Chris Stock, Efrain Rodriguez, Franz Demmel, Russell Ewings, Ch. Niedermayer, Yixi Su, Jose Rodriguez, Sang-Wook Cheong, K. Nemkovski, Mark Laver CaFe2O4 is a S=5/2 anisotropic antiferromagnet based on zig-zag chains having two competing magnetic structures (denoted as the A and B phases) which differ by the c-axis stacking of ferromagnetic stripes [1]. We apply neutron scattering to demonstrate that the competing orders result in magnetic antiphase boundaries separating these two order parameters at low temperatures. Neutron diffraction and bulk susceptibility find that the spins near these boundaries are weakly correlated and carry an uncompensated moment. Using high resolution neutron spectroscopy, we find that these boundaries are confining and measure a series of 9 quantized spin wave levels at low temperatures [2]. The competing anisotropic order parameters affords both localization of spin waves and also orphan spins in a classical magnet. |
Tuesday, March 6, 2018 3:42PM - 3:54PM |
H23.00007: THz Absorption Spectroscopy Study of Spin Waves in Orthoferrite YFeO3 Kirill Amelin, Toomas Room, Urmas Nagel, Randy Fishman, Je-Guen Park, Hasung Sim, Kisoo Park, Yoshiyuki Yoshida YFeO3 has an orthorhombic distorted perovskite structure of Pnma symmetry group. Below Néel temperature of about 655 K, the Fe spins S=5/2 arrange in an antiferromagnetic (AFM) state Γ4(Ga,Fc,Ab) with canted spins and a weak ferromagnetic component along the c axis. This complex spin structure is described by a combination of AFM nearest-neighbor couplings, Dzyaloshinsky-Moriya (DM) interactions and single-ion anisotropies. |
Tuesday, March 6, 2018 3:54PM - 4:06PM |
H23.00008: THz spectroscopy of spin waves in multiferroic LiFePO4 in high magnetic fields Laur Peedu, Toomas Room, Urmas Nagel, Sandor Bordäcs, Istvan Kezsmarki, Vilmos Kocsis, Yusuke Tokunaga, Yasujiro Taguchi, Yoshinori Tokura LiFePO4 belongs to the family of multiferroic lithium ortho phosphates compounds where the entanglement of magnetization and electric polarization leads to variety of magnon modes in the THz range that have dynamic electric and magnetic properties. Thus it is important to study THz absorption selection rules of magnons to understand the magneto electric properties of these materials. LiFePO4 orders antiferromagnetically below 50 K. We used THz absorption spectroscopy to measure magnon excitations in LiFePO4 single crystals below 5 K in zero and in magnetic fields up to 17 T. Several optically active magnons were observed. From the polarization dependence of absorbed THz radiation we found magnetic- and electric-dipole active magnons, and also a prototypical example of magneto-electric excitation. |
Tuesday, March 6, 2018 4:06PM - 4:18PM |
H23.00009: Non-reciprocal microwave response of antiferromagnetic magnons in a multiferroic Ba2MnGe2O7 Yusuke Iguchi, Yoichi Nii, Hiroshi Murakawa, Noriaki Hanasaki, Yoshinori Onose Simultaneously time-reversal and spatial-inversion symmetry breakings provide the non-reciprocal propagation of electromagnetic waves. The non-reciprocity means the difference of refractive indeces between oppositely propagating waves. This is called the non-reciprocal directional dichroism (NDD)[1]. The NDD has been observed in terahertz region by using the antiferromagnetic magnon excitation of multiferroics[2]. However the NDD owing to the antiferromagnetic magnon excitation has not been reported in microwave region, because almost antiferromagnets have large magnetic anisotropy and exchange interaction. Here, we show that the multiferroic Ba2MnGe2O7[3] has the two antiferromagnetic magnon modes in microwave region and that the magnon modes provide the NDD in microwave region. |
Tuesday, March 6, 2018 4:18PM - 4:30PM |
H23.00010: Surface acoustic wave on a multiferroic material CuB2O4 and magnon-phonon coupling. Ryo Sasaki, Yoichi Nii, Yoshinori Onose We successfully excited surface acoustic wave on a typical multiferroic material CuB2O4. |
Tuesday, March 6, 2018 4:30PM - 4:42PM |
H23.00011: Cooperative Density Waves and Superconductivity in La2CuO4+y Jiajia Wen, Wei He, Hoyoung Jang, Rebecca Smaha, Claudio Mazzoli, Stuart Wilkins, Jun-Sik Lee, Young Lee Cuprate high-temperature superconductors feature a complex phase diagram where various forms of symmetry breaking are found in close proximity to superconductivity (SC). Recent ubiquitous observations of charge density wave order (CDW) across families of cuprate superconductors suggest CDW a genuine instability of the doped CuO2 plane. Here we report resonant soft x-ray scattering (RSXS) study of CDW in La2CuO4+y, which features 3-dimensional ordering of oxygen dopants, and simultaneous onset of SC and spin density wave (SDW) at Tc ~ 42 K. Emerging first well above Tc, the CDW in La2CuO4+y is found to be dramatically enhanced below Tc. This contrast with previous observations in other cuprate superconductors where the CDW is suppressed by the onset of SC. Our results on La2CuO4+y provide evidence of cooperative relationship between CDW, SDW, and SC in a clean cuprate superconductor, and further corroborate the view point of "intertwined orders" to describe the complex electronic orderings in strongly correlated materials. |
Tuesday, March 6, 2018 4:42PM - 4:54PM |
H23.00012: Incommensurate Phonon Anomaly and the Nature of Charge Density Waves in Cuprates Hu Miao, Daisuke Ishigawa, rolf Heid, Matthieu le Tacon, Gilberto Fabbris, Derek Meyers, Genda Gu, Alfred Baron, Mark Dean While charge density wave (CDW) instabilities are ubiquitous to superconducting cuprates, the different ordering wavevectors in various cuprate families have hampered a unified description of the CDW formation mechanism. Here we investigate the temperature dependence of the low energy phonons in the canonical CDW ordered cuprate La1.875Ba0.125CuO4. We discover that the phonon softening wavevector associated with CDW correlations becomes temperature dependent in the high-temperature precursor phase and changes from a wavevector of 0.238 reciprocal space units (r.l.u.) below the ordering transition temperature up to 0.3 r.l.u. at 300 K. This high-temperature behavior shows that ``214''-type cuprates can host CDW correlations at a similar wavevector to previously reported CDW correlations in non-``214'' type cuprates such as YBa2Cu3O6+x. This indicates that cuprate CDWs may arise from the same underlying instability despite their apparently different low temperature ordering wavevectors. |
Tuesday, March 6, 2018 4:54PM - 5:06PM |
H23.00013: Visualizing How Electrons Delocalize and Couple to Bosons in a Doped Correlated Insulator Lorenzo Vistoli, Marius-Adrian Husanu, Anke Sander, Federico Bisti, Andrey Mishchenko, Vincent Garcia, Manuel Bibes, V. Strocov Most ABO3 transition metal perovskite oxides are insulating due to the strong Coulomb repulsion between electrons at the transition metal (B) and at the oxygen ions. As aliovalent A ions are introduced, the material usually transitions to a metallic state. However, the critical dopant concentration is often large and accompanied by structural changes, obscuring the study of band formation in these materials. In CaMnO3, minute doping induces a sharp transition to a metallic state. This compound thus appears as an ideal platform to explore the interplay between doping, correlations and disorder in perovskite oxides. Here, we use angle-resolved photoemission spectroscopy to determine the electronic structure of doped CaMnO3 thin films. We show that doping promotes the formation of several Fermi pockets with dispersive and non-dispersive bands, coexisting with polaronic signatures and quasiparticle mass renormalization signaling coupling to plasmonic excitations. These data shed light on the complex transport response of Ce-doped CaMnO3 and suggest strategies to engineer two-dimensional quantum matter from correlated oxides. |
Tuesday, March 6, 2018 5:06PM - 5:18PM |
H23.00014: Numerical study of photon spectroscopies for transition-metal oxides and complexes Chunjing Jia, Ilkyu Lee, Brian Moritz, Thomas Devereaux X-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) have become important techniques for understanding low-energy excitations in transition-metal oxides and electronic transitions transition-metal complexes. A theoretical understanding of these photon spectroscopies for such correlated systems has remained a challenge, especially for understanding momentum dependence and photon-polarization. Here we present the charge transfer full atom multiplet method using exact diagonalization technique for material-specific XAS and RIXS calculations with only minimum adjustable parameters. A few examples such as bulk NiO and molecular Ferrocyanide will be presented and compared with experiments. |
Tuesday, March 6, 2018 5:18PM - 5:30PM |
H23.00015: Search for a second frequency signal in magnetite (Fe3O4) in the TV –TW range:
a Maximum-Entropy μSR study C Morante, Carolus Boekema The local magnetism in Fe3O4 has been previously studied through muon-spin rotation (μSR) showing a single frequency signal. [1] Results indicate a transitionat TV (123 K) for the Verwey transition and a transition at TW (247 K) about twice TV . The transition at TW is not well understood, but suspected to be a precursor of the Verwey transition. [1] μSR time series of single crystals of magnetite indicate at a beat pattern, suggesting a second signal. By means of Maximum Entropy, we analyze transverse and zero field μSR single Xtal Fe3O4 data to search for a second signal in the T range above TV and below TW. [2]. The existence of this second signal of Fe3O4 in the TV -TW region could be related a phonon-assisted 3d-electron hopping in Fe3O4. [3] Thus, a second frequency signal or lack thereof in low fields may lead to a better understanding of the local magnetism, conduction mechanism, the Verwey transition and its precursors in the Fe3O4 Mott-Wigner glass. |
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