Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session P23: Magnetic Phenomena in Bulk Oxides: TheoryFocus
|
Hide Abstracts |
Sponsoring Units: GMAG DMP DCOMP Chair: Hyowon Park, University of Illinois at Urbana–Champaign Room: LACC 402B |
Wednesday, March 7, 2018 2:30PM - 2:42PM |
P23.00001: Percolation of frustrated polarons in doped cobaltite La1-xSrxCoO3-δ (LSCO) Peter Orth, Daniel Phelan, Chris Leighton, Rafael Fernandes Due to fascinating phenomena such as magneto-electronic phase separation and Co ion spin-state transitions, the archetypal cobaltite La1-xSrxCoO3-δ (LSCO) remains of high interest. Replacing La by Sr in the diamagnetic and insulating parent compound LaCoO3-δ introduces holes and magnetic moments. As Co undergoes spin-state transitions, 7-site spin polarons form at small x with a spin-per-Sr of S=12.5. Further doping leads to a glassy magnetic state and finally to a ferromagnetic (FM) metal at x=0.18. As simple statistical considerations predict a percolation of polarons already at x=0.05, the question arises what suppresses the formation of a macroscopic FM cluster. |
Wednesday, March 7, 2018 2:42PM - 2:54PM |
P23.00002: Why rare-earth ferromagnets are so rare: insights from the p-wave Kondo model Onur Erten, Shadab Ahamed, Roderich Moessner Magnetic exchange in Kondo lattice systems is of the Ruderman-Kittel-Kasuya-Yosida type, whose sign depends on the Fermi wave vector, kF. In the simplest setting, for small kF , the interaction is predominately ferromagnetic, whereas it turns more antiferromagnetic with growing kF. It is remarkable that even though kF varies vastly among the rare-earth systems, an overwhelming majority of lanthanide magnets are in fact antiferromagnets. To address this puzzle, we investigate the effects of a p-wave form factor for the Kondo coupling pertinent to nearly all rare-earth intermetallics. We show that this leads to interference effects which for small kF are destructive, greatly reducing the size of the RKKY interaction in the cases where ferromagnetism would otherwise be strongest. By contrast, for large kF, constructive interference can enhance antiferromagnetic exchange. Based on this, we propose a new route for designing ferromagnetic rare-earth magnets. |
Wednesday, March 7, 2018 2:54PM - 3:06PM |
P23.00003: Landau Theory of Multipolar Order in Pr(TM)2X20 Kondo materials SungBin Lee, Frederic Freyer, Jan Attig, Arun Paramekanti, Simon Trebst, Yong-Baek Kim A series of Pr(TM)2X20 (with TM=Ti,V,Rh,Ir and X=Al,Zn) Kondo materials exhibits exotic behavior such as quadrupolar order, superconductivity and non-Fermi liquid behavior. In particular, non-Kramers Pr3+ 4f2 moments show interesting magnetic field dependence with multipolar orderings. |
Wednesday, March 7, 2018 3:06PM - 3:18PM |
P23.00004: Ferromagnetism of local uranium moments in UBeGe Andreas Leithe-Jasper, Roman Gumeniuk, Walter Schnelle, Michael Nicklas, Alexander Yaresko, Kristina Kvashnina, Christoph Henning, Yuri Grin The new intermetallic uranium beryllium germanide UBeGe and its thorium reference compound ThBeGe crystallize with the hexagonal ZrBeSi type of structure. Studies of magnetic, thermal and transport properties reveal UBeGe to be a strongly uniaxial ferromagnet with two magnetic transitions at TC(1) =160 K and TC(2) =150 K. ThBeGe is a diamagnetic metallic system with low density of states at the Fermi level. The high magnetic moment, x-ray absorption near-edge spectroscopy as well as theoretical DFT calculations indicate localized U 5f2 states in UBeGe. |
Wednesday, March 7, 2018 3:18PM - 3:30PM |
P23.00005: Structural complexity and magnetic phase transformations: 4f electron-interplay Arjun Pathak, Y Mudryk, Vitalij Pecharsky Compounds that respond to varying magnetic field (H), pressure (p), temperature (T), or composition (x) by exhibiting structural or/and magnetic phase transformations are an intriguing subject matter for materials science, chemistry, and physics communities. Here we show that unlike the parent binaries – DyCo2 and ErCo2 – which exhibit lone distortions at their respective Curie temperatures, TC, a mixed pseudobinary Er0.75Dy0.25Co2 demonstrates two successive magnetostructural transitions: a first order at TC, followed by a second order below TC. Surprisingly, the ground state phase adopts Imma symmetry instead of the commonly observed Fddd. We show that the unusual sequence of structurally and magnetically distinct phases in Er1-xDyxCo2 can be judiciously controlled via 4f electrons, where Er and Dy – two next near neighbor lanthanides – each play a distinct role in defining phase stability (PRB 96, (2017) 064412). |
Wednesday, March 7, 2018 3:30PM - 3:42PM |
P23.00006: New Theoretical Characterizations for Half-Metallic Ferromagnets Pastor Chura, Kevin Bedell In the current literature Half-Metallic Ferromagnets (HMFs) have been theoretically characterized mainly by using the Band Theory approach. As a matter of fact, a first standard characterization of HMFs states that a HMF is a ferromagnet in which spin-up electrons have metallic band structure whereas spin-down electrons have insulating or semiconducting band structure. A second standard characterization says that a HMF is a ferromagnet in which at T=0K the density of states for the spin-down component at the Fermi level is zero whereas the density of states for the spin-up component at the Fermi level is different from zero. In this work, we propose new ways of theoretically characterizing HMFs by using an approach based on Fermi Liquid Theory for Spin Polarized Systems and the concept of exchange splitting, These new characterizations have proved to be useful in describing the thermodynamics and spin dynamics of HMFs in a way consistent with experiment. |
Wednesday, March 7, 2018 3:42PM - 3:54PM |
P23.00007: Magnetic and orbital order in 2D electron gases at (111) oxide surfaces and interfaces Nazim Boudjada, Gideon Wachtel, Arun Paramekanti Recent experiments have explored two-dimensional electron gases (2DEGs) at oxide (111) surfaces and interfaces. We discuss many-body instabilities of such (111) 2DEGs, incorporating multiorbital interactions in the t2g manifold which can induce diverse magnetic and orbital orders. Such broken symmetries may lead to electronic nematicity in transport, which could cooperate or compete with phonon mechanisms. We present an effective field theory for the interplay of magnetism and nematic charge order, and discuss implications of the nematicity for transport in (111) 2DEGs. |
Wednesday, March 7, 2018 3:54PM - 4:06PM |
P23.00008: Quantum Phase Transitions in a Multi-orbital Hubbard Model with Spin-Orbit Coupling Nitin Kaushal, Jacek Herbrych, Alberto Nocera, Gonzalo Alvarez, Adriana Moreo, Fernando Reboredo, Elbio Dagotto We used the density matrix renormalization group technique to perform a detailed study of the effect of spin-orbit coupling on a three-orbital Hubbard model in one dimension [1]. Fixing the Hund coupling to a robust value compatible with some multiorbital materials, we present the phase diagram varying the Hubbard U and spin-orbit coupling λ, at zero temperature for n=4 [2]. We also present the doping and spin-orbit coupling λ phase diagram, for intermediate and strong Hubbard U [3]. Among many results, we observe an interesting transition from an orbital-selective Mott phase to an excitonic insulator with increasing λ at intermediate U. In the strong U coupling limit, we find a nonmagnetic insulator with an effective angular momentum〈(Jeff)2〉≠0 near the excitonic phase, smoothly connected to the 〈(Jeff)2〉= 0 regime. In the same model we also found a novel and robust excitonic insulator phase with Block spin ordering, at various dopings and in both the intermediate and strong coupling region. |
Wednesday, March 7, 2018 4:06PM - 4:18PM |
P23.00009: Ultrafast optically induced magnetic phase transition in GdTiO3 from first-principles Guru Bahadur Khalsa, Nicole Benedek Recent development of intense ultrashort mid and far infrared laser sources has created an opportunity for functional materials based on direct excitation of infrared active phonons. Strong excitation of infrared active phonons can produce large unidirectional distortions of the crystal structure through special non-linear coupling1-4. Complex oxides provide an important test-ground for this experimental approach due to their diversity, strong coupling to optical fields, and demonstrated connection between subtle structural changes and fundamental properties. Early experiments in complex oxides are intriguing - suggesting that this mechanism can transiently induce insulator-metal phase transitions1 and enhance superconductivity2. Hidden A-type antiferromagnetism (A-AFM) has been predicted in rare-earth titanates (between SmTiO3 and GdTiO3) but not found using static techniques like solid solution or strain. We show how optical excitation of infrared phonons gives dynamical access to the A-AFM phase in GdTiO3 through Jahn-Teller and Gd distortions that are challenging to access with static techniques. |
Wednesday, March 7, 2018 4:18PM - 4:30PM |
P23.00010: SU(6) Symmetry in a Model of Lattice Electrons: The Case of NaTiSi2O6 Weiguo Yin, Alexei Tsvelik, Emil Bozin Dimerization of Ti3+ ions in NaTiSi2O6, a quasi-one-dimensional Mott insulator, has attracted considerable attention due to its possibility as a rare inorganic spin-Peierls material. Recently based on two-orbital models, it was suggested that this material has an orbital-assisted Peierls ground state [1]. Here we point out that in an ideal case, a remarkable property of NaTiSi2O6 is that its electronic band is exactly 3 times degenerate—with the lattice period of six Ti ions along the chain structure—despite the crystal field splitting of the three t2g orbitals into a local doublet and a higher energy singlet. We thus study NaTiSi2O6 in proximity to this case using density-functional theory and the SU(6)-symmetric Sutherland Hamiltonian. The perturbation from electron-lattice interactions breaks the SU(6) symmetry, leading to a spontaneous dimerization accompanied by a structural distortion having the characteristic length of about six Ti-Ti bonds. |
(Author Not Attending)
|
P23.00011: NMR in an electric field: a bulk probe of the hidden spin and orbital polarizations Ion Garate, Samuel Boutin, Jorge Ramirez-Ruiz Recent theoretical work has established the existence of hidden spin and orbital textures in non-magnetic materials with inversion symmetry. Here, we propose that these textures can be detected by nuclear magnetic resonance (NMR) measurements carried out in the presence of an electric field. In crystals with hidden polarizations, a uniform electric field produces a staggered magnetic field that points to opposite directions at atomic sites related by spatial inversion. As a result, the NMR resonance peak corresponding to inversion partner nuclei is split into two peaks. The magnitude of the splitting is proportional to the electric field and depends on the orientation of the electric field with respect to the crystallographic axes and the external magnetic field. As a case study, we will present the theory of electric-field-induced splitting of 209Bi peaks in Bi2Se3. We will also mention other potentially more promising candidate materials, whose crystal symmetry enables strategies to suppress the linewidth produced by the Oersted field. |
Wednesday, March 7, 2018 4:42PM - 4:54PM |
P23.00012: Phase transitions in the Hubbard model studied by a cluster slave spin method Wei-Cheng Lee, Ting-Kuo Lee The cluster slave-spin method is introduced to systematically investigate the solutions of the Hubbard model including the symmetry-broken phases. In this method, the electron operator is factorized into a fermionic spinon describing the physical spin and a slave-spin describing the charge fluctuations. We show that the self-consistent equations to explore various symmetry-broken density wave states can be constructed in general with a cluster of multiple slave-spin sites, and we employ this method to study the antiferromagnetic (AFM) state in the single band Hubbard model with the two- and four-site clusters of slave spins. We find that the cluster slave-spin method can capture correct behaviors in both weak- and strong- coupling limit within a unified framework. In addition, the holon-doublon correlator as functions of U and doping x is also computed, which exhibits a strong tendency toward the holon-doublon binding in the strong coupling regime. We further show that the results are progressively improved as the cluster is enlarged from a single site to four sites. Our results demonstrate that the cluster slave-spin method can be a powerful tool to systematically investigate the strongly correlated system. |
Wednesday, March 7, 2018 4:54PM - 5:06PM |
P23.00013: Shining Light on Spin-Orbital Separation Tamas Palmai, Andrew James, Robert Konik We consider shining light on a quasi-one-dimensional Mott insulator exhibiting spin-orbital separation. The low-energy sector of such a compound can be described by a spin chain with additional orbital degrees of freedom. Starting from an initial state with a highly polarized orbital sector, depending on the direction and polarization of the light, different orbitals can be activated or deactivated to take part in the time evolution. By employing a combination of Floquet theory and numerical methods, we find that orbital polarization can be controlled by a chirped laser. We discuss our results in connection to pump-probe experiments on the one dimensional spin-orbital chain compound Sr2CuO3. |
Wednesday, March 7, 2018 5:06PM - 5:18PM |
P23.00014: Z2 topological order near the Neel state of the square lattice antiferromagnet Shubhayu Chatterjee, Subir Sachdev, Mathias Scheurer We classify quantum states proximate to the Neel state of the spin S=1/2 square lattice antiferromagnet with two-spin near-neighbor and four-spin ring exchange interactions. Motivated by recent experiments on the cuprates and the iridates, we examine states with Z2 topological order, an order which is not present in the semiclassical limit. Some of the states break one or more of reflection, time-reversal, and lattice rotation symmetries, and can account for the observations. Such states can also be generalized to metals at finite doping, and may have implications for the pseudogap phase of the cuprates. |
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