Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E40: Magnetic Excitations in OxidesFocus
|
Hide Abstracts |
Sponsoring Units: GMAG DMP Chair: Sachith Dissanayake, Duke University Room: BCEC 208 |
Tuesday, March 5, 2019 8:00AM - 8:36AM |
E40.00001: Optical signatures of a 3D electronic liquid crystal in Cd2Re2O7 Invited Speaker: David Hsieh In the presence of strong interactions, the fluid of mobile electrons in a metal can spontaneously break the point group symmetries of its underlying host lattice, forming an electronic analogue of a classical liquid crystal. The experimental discovery of 2D electronic liquid crystals (ELCs) was first made nearly 20 years ago in semiconductor heterostructures and has since been reported in many other systems including the copper- and iron-based high-temperature superconductors. However whether or not a 3D version of an ELC can exist has remained unclear. In this talk, I will present signatures of a 3D ELC in the strongly spin-orbit coupled metallic pyrochore Cd2Re2O7 detected using ultrafast coherent phonon spectroscopy and a recently developed spatially-resolved nonlinear optical polarimetry technique. |
Tuesday, March 5, 2019 8:36AM - 8:48AM |
E40.00002: Nature of magnetic excitations in the spin-1/2 triangular antiferromagnet Ba3CoSb2O9 in applied magnetic field Luwei Ge, Qing Huang, Tao Hong, Haidong Zhou, Jie Ma, Martin Mourigal Ba3CoSb2O9 is one of the very few experimental realizations of the spin-1/2 triangular antiferromagnets. Despite the model being extensively studied, a unified understanding of the compound’s zero-field magnetic excitations has not yet been achieved. Spin-wave theory up to 1/S correction clearly failed to describe the whole picture. However, whether this is indeed due to the intrinsic nature of the spin Hamiltonian remains debatable. Seeking more experimental evidence, we investigated the system’s field-induced states with inelastic neutron scattering, particularly in the low-field regime. While revealing some yet unexplained features, our results show some strong damping of the excitation branch around K point, consistent with the field-induced magnon decay scenario. Our results are expected to help obtain a better understanding the system. |
Tuesday, March 5, 2019 8:48AM - 9:00AM |
E40.00003: Optical properties, lattice dynamics, and structural phase transition in polar magnets Fe2Mo3O8 and Mn2Mo3O8 T.N. Stanislavchuk, Andrei Sirenko, A. P. Litvinchuk, Zhenxian Liu, Yazhong Wang, G.L. Pascut, Valery Kiryukhin, Sang-Wook Cheong Optical properties and lattice dynamics of hexagonal M2Mo3O8 (M = Fe, Mn) single crystals are studied in a wide temperature range by means of infrared (IR) reflectivity and Raman scattering at the temperatures above and below the magnetic transitions. Experimental data for optical phonons are compared to group theoretical mode analysis and complimentary DFT and DMFT lattice dynamics calculations. At temperatures below TN(Fe)=60 K several additional IR- and Raman-active modes are detected in experimental spectra of Fe2Mo3O8. We also found several IR-active modes in the 2500 – 3500 cm-1 range in Fe2Mo3O8 at low temperatures. We attribute them to optical transitions from the ground state to the split levels of the 5T2 state of Fe2+ ions in the tetrahedral coordination. |
Tuesday, March 5, 2019 9:00AM - 9:12AM |
E40.00004: Non-Reciprocal Directional Dichroism of THz Radiation in Multiferroic Sr2CoSi2O7 Johan Viirok, Urmas Nagel, Toomas Room, Dániel Gergely Farkas, Peter Balla, Dávid Szaller, Vilmos Kocsis, Yusuke Tokunaga, Yasujiro Taguchi, Yoshinori Tokura, Bence Bernáth, Dmytro Kamenskyi, Istvan Kezsmarki, Sandor Bordacs, Karlo Penc Directional dichroism (DD) is the effect when material absorbs light beams travelling in opposite direction differently. At THz frequencies DD has been found in multiferroics with magnetic and charge order. In these materials the spin waves are coupled to the oscillations of electric polarization. A spin wave acquires electric dipole activity due to optical magnetoelectric (ME) coupling and therefore interacts with the electric component of the THz radiation in addition to magnetic component. |
Tuesday, March 5, 2019 9:12AM - 9:24AM |
E40.00005: Resonant inelastic x-ray scattering study the evolution of spin and charge excitations in La2-xCexCuO4 combi-films Jiaqi Lin, Jie Yuan, Schmitt Thorsten, Kejin Zhou, kui jin, Xuerong Liu We present resonant inelastic x-ray scattering (RIXS) study of spin and charge excitations in La2-xCexCuO4 combi-films. The doping level of the film changes continuously from one tip to the other, nominally x=0.10 to x=0.19. Doping dependence is accomplished by simply translating the film in a fine step along the doping gradient direction. We explored the evolution of spin and charge excitations from an optimal doped superconductivity at x=0.11 to an overdoped fermi liquid at x=0.18. As doping, the energy of both spin and charge excitations is hardening. For the width, the spin excitation is broadening, and the charge excitation becomes sharpening. In addition, we performed L and incident energy dependence measurements to examine the characteristics of two excitations. Spin excitation does not have L dependence nor incident energy dependence, while charge excitation has L dependence and slightly incident energy dependence. This indicates spin and charge excitations are not the two faces of the coin. Instead, spin and charge excitations are derived from short-range correlation and long-range Coulomb interaction, respectively. |
Tuesday, March 5, 2019 9:24AM - 9:36AM |
E40.00006: Dimensional Reduction in BaCuSi2O6 Investigated by Neutron Scattering Stephan Allenspach, Alun M Biffin, Uwe Stuhr, Gregory Tucker, Seiko Ohira-Kawamura, Maiko Kofu, David J. Voneshen, Nicolas Laflorencie, Frederic Mila, Christian Rueegg Quasi low-dimensional systems tipically display a dimensional crossover into 3D behavior either because of a diverging correlation length close to a critical point or due to vanishing thermal fluctuations when approaching zero temperature. Contrary to this, the quantum magnet BaCuSi2O6, which consists of stacked 2D layers hosting spin dimers, undergoes a dimensional reduction from 3D to 2D in close vicinity to the quantum critical point to its Bose Einstein Condensate phase [1]. Mechanisms for this dimensional reduction were proposed based on frustration of the interlayer exchange resulting from an assumed antiferromagnetic intralayer exchange. However, density-functional theory calculations suggest a ferromagnetic intralayer exchange which would render such a frustration impossible [2]. We have performed high-resolution neutron spectroscopy experiments and calculated the excitation spectrum for various dimer models. Our results suggest that the intralayer exchange is ferromagnetic, while there exist at least three different dimer types in BaCuSi2O6. We conclude that the existence of different dimer types might lead to 2D behavior in close vicinity to the quantum critical point. |
Tuesday, March 5, 2019 9:36AM - 9:48AM |
E40.00007: Hysteresis of THz dielectric permittivity below TNeel in CaFe2O4 Daniel Heligman, Thuc Mai, Lunyong Zhang, Jae Wook Kim, Sang-Wook Cheong, Rolando Valdes Aguilar CaFe2O4 is a quantum antiferromagnet that exhibits an interplay between two different magnetic phases below TNeel ~ 200 K. We have analyzed the terahertz (THz) response of CaFe2O4 for the polarization configuration hω||c and eω||b and observed a significant change in the spectrum between 80 K and 120 K for frequencies above 900 GHz. The THz dielectric permittivity shows hysteresis between 80 K and 120 K that does not occur for any other orientations. In addition, we have observed a magnon with a frequency of 840 GHz at 10 K that red shifts with increasing temperature until 70 K. At which point, its spectral weight decreases rapidly, while at the same time a lower frequency magnon gains intensity. This behavior is only observed for hω||c irrespective of the direction of the electric field of the THz pulse. These behaviors seem to be associated with the decrease in the population of the B magnetic phase and simultaneous increase in the population of the A phase around 100 K. |
Tuesday, March 5, 2019 9:48AM - 10:00AM |
E40.00008: H-ErMnO3 electrodynamics from far-infrared emission, reflectivity, and absorption in the ferroelectric and paraelectric phases Nestor Massa, Leire del Campo, Karstern Holldack, Vinh Ta Phuoc, Patrick Etchegut, Paula Kayser, José Antonio Alonso We report on the temperature evolution of ambient non-centrosymmetric hexagonal H-ErMnO3 -P63cm-(Z=6) from 2 K to decomposition as seen in absorption, near normal reflectivity, and emission spectra in the THz to mid-infrared spectral range. While up to 300 K our measurements are in agreement with known spectra, in the ferroelectric phase below TC~833 K, there is a strong continuous change in phonon profiles involving the two non-equivalent Er sites and bipyramids tilting. Three weak but sharp lowest frequency-lower temperature hybrid modes also melt into the background at about Tc. In emission spectra, toward the paraelectric centrosymmetric (P63 /mmc, Z=2) phase, an optical conductivity mid-infrared intraband becomes distinctive. It peaks at ~5000 cm-1 and has the energy and profile fingerprint of small polarons (bipolarons). Its intensity depends on electric dipole ordering. At 900 K, just above TC, this pronounce band starts a continuous weakening shifting to lower frequencies up to the temperature triggering hopping conduction onset of decomposition. We propose that oxygen polarizability (partially delocalized 2p-electrons) is a main dynamical constituent for bipolarons in cooperative driven MnO5 bipyramids and thus in spontaneous ferroelectric polarization. |
Tuesday, March 5, 2019 10:00AM - 10:12AM |
E40.00009: Managing magnon transport properties in bulk magnetic oxides within mesoscopic Boltzmann methods Yanxia Wang, Tao Liu, Wei Wang, YuHeng Li, Jianwei Zhang The bulk transport properties of magnon in magnetic oxides layers demand precise physical understanding of magnon diffusion,scattering and relaxation processes. In this work, we invent a novel magnon Boltzmann equation from full quantum magnon Hamiltonian. With changing thickness of magnetic oxide film(YIG), our numerical results on magnon accumulation and current shows there are two different processes in bulk magnon transport: diffusion region and relaxation region. Furthermore, we theoretically discover physical origin for decreasing of magnon diffusion length with increasing magnetic field H, it was olny observed in preivous experimental works. And since magnon relaxation closely related to many magnons scattering, a new spatial dependent draft field was introduced, similar to anisotropy, which was describing collective local motion of magnon. More importantly, our results show magnon current can be manipulated by varying of anisotropy in magnetic oxides, especially in strong anisotropic energy materials, such as NiFe2O4 or CoFe2O4. In this framework, we also provide the methods to adjust the magnon transport with applying gradient magnetic field and gradient T field. |
Tuesday, March 5, 2019 10:12AM - 10:24AM |
E40.00010: Spin Structure Models of YFeO3 from THz Spectroscopy Study Kirill Amelin, Urmas Nagel, Randy Fishman, Yoshiyuki Yoshida, Hasung Sim, Kisoo Park, Je-Guen Park, Toomas Room In YFeO3 iron spins S=5/2 arrange in an antiferromagnetic (AFM) canted state Γ4(Ga,Fc,Ab) well above room temperature. With four spins per unit cell, its spin structure is described by a combination of exchange interactions, Dzyaloshinskii-Moriya (DM) interactions, and single-ion anisotropies (SIA). Since only Fe ions have the non-zero magnetic moment, this compound is a perfect modelling system for spin interactions and a step towards understanding more complex materials, possibly those with multiferroic properties. |
Tuesday, March 5, 2019 10:24AM - 10:36AM |
E40.00011: Terahertz emission spectroscopy of YIG | topological insulator bilayers Evan Jasper, John S Jamison, Timothy Pillsbury, Anthony R. Richardella, Nitin Samarth, Roberto Myers, Rolando Valdes Aguilar Building on the demonstration of terahertz (THz) emission spectroscopy (TES) in metallic ferromagnet|normal metal heterostructures, recent works have now observed the THz emission from heterostructure bilayers of both yttrium iron garnet (YIG) | Pt and Co | Bi2Se3. We examine the energy dependence of the spin-charge conversion efficiency of THz emission in samples of a few quintuple layers of Bi2Se3 and (Bi.24Sb.76)2Te3 grown on YIG(100) and YIG(111) substrates. We excite the samples with ultrafast femtosecond light pulses of both 1.55 eV and 3.10 eV. At 1.55 eV, no electrons in YIG are excited above the band gap of 2.85 eV. When we double the photon energy to 3.10 eV, electrons in the YIG are excited into the conduction band. Since both photon energies emit THz radiation, we expect that in each case the mechanism of emission will be attributed to different effects. Specifically, with excitations of 1.55 eV, the spin current process should be predominately generated by the spin-Seebeck effect. With excitations of 3.10 eV, the generation of spin current should be dominated by the direct photoexcitation of spin-polarized charge carriers. |
Tuesday, March 5, 2019 10:36AM - 10:48AM |
E40.00012: WITHDRAWN ABSTRACT
|
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700