Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session A50: Antiferromagnetic Order and Instabilities |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Md Mofazzel Hosen Room: Mile High Ballroom 1C |
Monday, March 2, 2020 8:00AM - 8:12AM |
A50.00001: First single crystals of a new itinerant antiferromagnet without magnetic elements Jaime Moya, Alannah Hallas, Emilia Morosan, Vaideesh Loganathan, Andriy Nevidomskyy, Franziska Weickert, James W Beare, Yipeng Cai, Graeme Luke, Chien-Lung Huang Magnetism exists on a spectrum spanning the local to itinerant limit. Theory in the local moment extreme is experimentally confirmed in many magnetic insulators where the magnetism originates from unfilled electronic shells. However, in the itinerant limit, where magnetism stems from band effects, experiment lags theory as there are only three known purely itinerant magnets: ZrZn_{2} and Sc_{3.1}In, both FM, and TiAu an AFM. While ZrZn_{2} has been made in single crystal form, no single crystals have been made of a purely itinerant AFM, until now. We present the results on single crystals of a new itinerant AFM with no magnetic constituent elements which orders at T_{N}= 11 K. The paramagnetic moment is large, 1.0 μ_{B}/FU, compared to the saturated moment of 0.25 μ_{B}/FU, leading to a Rhodes-Wohlfarth ratio of 4. The entropy release is small, just 0.7%Rln2, yet muon spin relaxation measurements confirm the order is intrinsic. DFT calculations confirm the small moment and conclude a Fermi surface nesting mechanism is responsible for the magnetic order. Having the first purely itinerant AFM crystal paves the way for advance experiments that will allow a fundamental understanding of this class of materials for the first time. |
Monday, March 2, 2020 8:12AM - 8:24AM |
A50.00002: Magnetochiral dichroism in a collinear antiferromagnet MnTiO_{3} with zero magnetization Tatsuki Sato, Nobuyuki Abe, Shojiro Kimura, Yusuke Tokunaga, Taka-hisa Arima Symmetry breaking induces specific optical effects. Magnetochiral dichroism (MChD) - nonreciprocal directional asymmetry in the propagation of unpolarized light - has been found to be induced by simultaneous breaking of the space-inversion and time reversal symmetries. After the first discovery [1], it has been established that net magnetization along with the light path causes MChD in various chiral magnets. In contrast, MChD in antiferromagnets without magnetization is less explored. |
Monday, March 2, 2020 8:24AM - 8:36AM |
A50.00003: Highly nonlinear magnetoelectric effect in antiferromagnetic Co_{4}Ta_{2}O_{9} single crystals Donggun Oh, Nara Lee, Sungkyun Choi, Jae Young Moon, Jong Hyuk Kim, Hyun Jun Shin, Hwan Young Choi, Son Kwanghyo, Matthias J Gutmann, Gideok Kim, Valery Kiryukhin, Jurgen Nuss, Young Jai Choi A class of antiferromagnetic honeycomb lattices compounds, A_{4}B_{2}O_{9} (A = Co, Fe, Mn; B = Nb, Ta), have been explored owing to the occurrence of linear magnetoelectricity. We observe a highly nonlinear magnetoelectric effect on single crystals of Co_{4}Ta_{2}O_{9} (CTO), distinctive from the linear behavior in the isostructural Co_{4}Nb_{2}O_{9}. Ferroelectricity emerges primarily along the [110] direction under magnetic fields, with the onset of antiferromagnetic order at T_{N} = 20.5 K. For in-plane magnetic field, a spin-flop occurs at H_{C} ≈ 0.3 T, above which the ferroelectric polarization gradually becomes negative and reaches a broad minimum. Upon increasing magnetic field further, the polarization crosses zero and increases continuously to ~60 μC/m^{2} at 9 T. In contrast, the polarization for a magnetic field perpendicular to the hexagonal plane increases monotonously and reaches ~80 μC/m^{2} at 9 T. This observation of a strongly nonlinear magnetoelectricity suggests that two types of inequivalent Co^{2+} sublattices generate magnetic field-dependent ferroelectric polarization with opposite signs. These results motivate fundamental and applied research on the intriguing magnetoelectric characteristics of these honeycomb lattice materials. |
Monday, March 2, 2020 8:36AM - 8:48AM |
A50.00004: Gapless antiferromagnetic behavior in newly synthesized marcasite-phase CoAsSe Yiyao Chen, George Yumnam, Ashutosh Dahal, Jose Rodriguez-Rivera, Guangyong Xu, Thomas Heitmann, Deepak K Singh CoAsSe belongs to the CoXY chalcogenide family and is reported to crystalize in different phases depending on the synthesizing temperature and pressure, including a half metallic phase according to DFT calculations. For the first time, we have synthesized marcasite-phase CoAsSe in large amount to perform neutron scattering measurements. Elastic neutron scattering measurements revealed weak magnetic peaks below T ~ 38 K at momentum transfer positions of (0, 0.5, 0) and (1, 0, 0) in reciprocal lattice units. Detailed inelastic measurements in low temperature revealed a broad excitation spectrum in the energy transfer-momentum transfer map. We will present the magnetic structures of the newly synthesized marcasite phase CoAsSe and discuss its relationship to electrical measurement results. |
Monday, March 2, 2020 8:48AM - 9:00AM |
A50.00005: Microscopic insights to ARPES spectra of doped quantum anti-ferromagnets Fabian Grusdt, Annabelle Bohrdt, Frank Pollmann, Michael Knap The phase diagram of cuprates, often modeled by the 2D Fermi Hubbard or $t-J$ model, remains poorly understood at low doping. Here we present new theoretical insights to the ARPES spectrum of quantum anti-ferromagnets at low doping: We argue that, at strong coupling $t \gg J$, the spectrum directly reflects the spectral function of a spinon which forms a universal bound state with the chargon created in the measurement. Our result is relevant to cuprates in the pseudogap regime: we interpret the the observed Fermi-arcs in a fractionalized Fermi liquid (FL*) picture and argue that the strongly suppressed spectral weight on the back-side of the hole pocket is a signature for the Dirac-fermion nature of the underlying spinons. We present DMRG calculations of the one-hole spectrum, which support the existence of the universal spinon-chargon bound state we assume at strong couplings. Our results are also relevant for the search of Dirac spinons in a larger class of frustrated quantum magnets. |
Monday, March 2, 2020 9:00AM - 9:12AM |
A50.00006: Optical conductivity of CrAs across the paramagnetic to antiferromagnetic transition Alexandre Zimmers, Ricardo Lobo, Amir-Abbas Haghighirad, Matthieu Le Tacon We report the optical spectroscopy of monopnictide crystal CrAs. This system exhibits a PM to AF transition at T_N~265K. This AF phase gradually disappears under pressure with the emergence of 2.2K superconductivity at 0.7GPa. To understand this rich phase diagram, various technics have investigated similarities of this material with the parent iron-pnictide superconductors. Here we studied the PM to AF transition by measuring the reflectivity from 300K to 5K at ambient pressure from 17meV to 3eV. As a function of incident photon energy, the reflectivity shows a gradual decay for all temperatures. The optical conductivity was extracted using Kramers–Kronig. Below 50meV, a Drude peak is clearly found only for temperatures below T_N. Extrapolation to zero frequencies of the conductivity is in agreement with previous reported DC transport measurements. In the mid-infrared range, the optical response of the AF order (T=250K) shows a rounded gap features with respect to the PM phase (T=300K): suppression in the low frequency optical conductivity, alongside a spectral weight transfer from low to high frequencies. The spectral weight transfer dip-hump structure will be compared to previous SDW gaps found in iron-based superconductors and electron doped cuprates. |
Monday, March 2, 2020 9:12AM - 9:24AM |
A50.00007: Gapless spin liquid state of the spin-1/2 honeycomb antiferromagnetic Gamma model Xiaoqun Wang, Qiang Luo, Jize Zhao We propose a choreographed model by introducing a bond-modulated Heisenberg interaction J in addition to the Gamma term. With varying an angular parameter of vartheta= atan}(Gamma/J)in[0,pi], the ground state is shown to change from a zigzag magnetic order to a stripy magnetic order through a mixed phase as well as a noncoplanar phase based on a parallel tempering Monte Carlo simulation. In the quantum case where we resort to large scale density matrix renormalization group calculations, two classical intermediate phases merge into one which is gapless and nonmagnetic, signaling a quantum spin liquid (QSL), in a wide range of 0.50\leq vartheta/pi\leq 0.66(1) for the thermodynamic limit. It turns out that the ground state of HCGammaA is affirmed to be the gapless QSL since it corresponds to vartheta=\pi/2 in the phase diagram. Our findings are further verified with scanning the variable parameter vartheta on a long cylinder. |
Monday, March 2, 2020 9:24AM - 9:36AM |
A50.00008: Evidence for a Field-Induced Quantum Phase Transition in Ising-like D-Er_{2}Si_{2}O_{7} Gavin Hester, Tim DeLazzer, Danielle Yahne, Colin Sarkis, Kate Ross Exploring the magnetic properties of the rare-earth pyrosilicate (RE_{2}Si_{2}O_{7}) family of compounds is of interest due to their variety of crystal structures and anisotropic pseudo-spin ½ moments. D-Er_{2}Si_{2}O_{7} (space group P2_{1}/b) was previously found to have a large g-tensor anisotropy (g_{xx} = 2.6, g_{yy} = 3.4, g_{zz} = 13.4) and magnetization consistent with Ising exchange [1]. In this work we have performed specific heat, magnetometry, and inelastic neutron scattering (INS) on a polycrystalline sample to further characterize the magnetism of D-Er_{2}Si_{2}O_{7}. The zero-field specific heat and magnetometry data corroborate previous measurements indicating antiferromagnetic ordering at 1.9 K. The INS data shows a gapped excitation at 0.6 meV in zero field, consistent with Ising exchange. This gap closes with the application of a magnetic field of ~1 T, consistent with a quantum critical point. Magnetization measurements on single crystal samples suggest that the mode softening is due to the field acting on the direction perpendicular to the Ising moments. Our data suggests that D-Er_{2}Si_{2}O_{7} could be a new experimental system in which to study the quantum Ising model. |
Monday, March 2, 2020 9:36AM - 9:48AM |
A50.00009: Nonthermal interacting-magnon dynamics in an optically driven 2D Heisenberg antiferromagnet Mona Kalthoff, Dante Kennes, Andrew Millis, Michael Sentef Recent theory results demonstrate a dynamical phase transition involving nonthermal magnon populations in the antiferromagnetic phase of the 2D Hubbard model upon laser driving [Walldorf et al., Phys. Rev. B 100, 121110(R) (2019)]. These results were obtained in a one loop non-interacting magnon theory. Here we present first steps towards a full interacting theory of this dynamical phase transition using a Dyson Maleev large Spin expansion and a Boltzmann formalism to investigate the effects of magnon-magnon interactions on the dynamical phase transition. The dynamical phase transition will be more completely characterized and implications for pump-probe experiments and ultrafast materials design of strongly correlated magnetism will be discussed. |
Monday, March 2, 2020 9:48AM - 10:00AM |
A50.00010: Coherently driven phonons coupled to antiferromagnetic order Valentin Kasper, Sergi Julia, Ravindra Chhajlany, Maciej A Lewenstein The possibility to coherently drive single phonon modes in strongly correlated materials opens the possibility to analyze and manipulate quantum matter via the electron-phonon coupling. In this work we study the effect of a single coherent phonon mode coupled to antiferromagnetic order. In particular, we calculate the dynamic spin structure factor and discuss the possibility of an emergent quasiparticle due to the coupling between phonons and magnons. Further, we explore the possibility to observe self-similar behavior in the occupation number of magnons. |
Monday, March 2, 2020 10:00AM - 10:12AM |
A50.00011: Refinement of exchange parameters and magnetic form factor of Mn_{3}Ir from neutron spectroscopy measurements. Martin D LeBlanc, Adam Aczel, Garrett E Granroth, Byron W Southern, Stephen E Nagler, Jiaqiang Yan, John P. Whitehead, Martin Plumer Inelastic neutron scattering measurements of the fcc kagome antiferromagnet Mn_{3}Ir were performed using the SEQUOIA spectrometer at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). Comparison of the observed magnetic excitations to calculated spin waves, using exchange parameters derived from Density Functional Theory (DFT) calculations^{1}, confirms that 4 exchange parameters are needed to describe the spectra. However the values from DFT underestimate the bandwidth of the excitations. Using these values as initial parameters, fits to the model modified the 2 largest exchange parameters to match the bandwidth. A spin orbit correction to the the magnetic form factor was also provided by the fit. These results are consistent with effective spin orbit coupling mentioned in^{2}. Physically this means the magnetic moment is more extended than the free ion value. |
Monday, March 2, 2020 10:12AM - 10:24AM |
A50.00012: Orbital magnetization in magnetic neutron scattering Hua Chen Magnetic neutron scattering has been a powerful tool to reveal the microscopic magnetic structures of ordered and disordered magnetic systems. For magnetically ordered crystalline systems it has been a common practice to fit the elastic neutron cross-section to models of periodically arranged localized magnetic moments. However, it is unclear how the orbital magnetization which has an itinerant nature manifests in neutron scattering. The question is relevant to, e.g., metallic antiferromagnets and 4d/5d transition metal materials. We show that magnetic neutron scattering in general maps out the equilibrium electric current distribution inside the material but leaves the magnetization density unfixed because of a gauge freedom. We discuss the connection between the equilibrium current density and the modern theory of orbital magnetization, and provide examples on calculating the orbital contribution to elastic neutron cross-section using models and first-principles methods. |
Monday, March 2, 2020 10:24AM - 10:36AM |
A50.00013: Numerical evidence for a continuous phase transition between Neel and valence bond solid phases on a spin-ladder system Takuhiro Ogino, Ryui Kaneko, Satoshi Morita, Naoki Kawashima We investigate the possibility of deconfined quantum criticality in the J-Q-like model in one spatial dimension. |
Monday, March 2, 2020 10:36AM - 10:48AM |
A50.00014: Monte Carlo study of microscopic models for Néel-to-plaquette VBS transition on 2D square lattice Jun Takahashi, Anders W Sandvik The theory of deconfined quantum criticality (DQC) predicts an interesting connection between the Néel and the valence-bond solid (VBS) states, resulting in critical quantum phase transitions beyond the Ginzburg-Landau paradigm with emergent higher symmetry [1]. |
Monday, March 2, 2020 10:48AM - 11:00AM |
A50.00015: Terahertz 2D coherent spectroscopy of transverse field quantum Ising model with further neighbor interactions Yihua Qiang, Yuriy Sizyuk, Thais Victa Trevisan, Peter Orth Recent advances in optical experimental methods in the terahertz range made terahertz 2D coherent spectroscopy (2DCS) possible. It has been a successful tool to probe interactions in various systems ranging from biexcitons in semiconductors to magnons in magnetic insulators. Here, we report results for the nonlinear 2DCS susceptibilities in the transverse field quantum Ising model including further neighbor interactions. Using a Jordan-Wigner transformation the model can be mapped to interacting fermions, for which we compute the 2DCS spectrum in a field-theoretical Keldysh approach. Information contained in the 2DCS can be used to identify interactions among the fermions, corresponding to next-nearest neighbor spin exchange couplings in the magnetic system. |
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