Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session C18: Iridates IFocus

Hide Abstracts 
Sponsoring Units: GMAG DMP Chair: Deepak Singh, Universityof Missouri Room: 317 
Monday, March 14, 2016 2:30PM  3:06PM 
C18.00001: Topological and unconventional magnetic states in transition metal oxides Invited Speaker: Gregory Fiete In this talk I describe some recent work on unusual correlated phases that may be found in bulk transition metal oxides with strong spinorbit coupling. I will focus on model Hamiltonian studies that are motivated by the pyrocholore iridates, though the correlated topological phases described may appear in a much broader class of materials. I will describe a variety of fractionalized topological phases protected by timereversal and crystalline symmetries: The weak topological Mott insulator (WTMI), the TI* phase, and the topological crystalline Mott insulator (TCMI). If time permits, I will also discuss closely related heterostructures of pyrochlore iridates in a bilayer and trilayer film geometry. These quasitwo dimensional systems may exhibit a number of interesting topological and magnetic phases. [Preview Abstract] 
Monday, March 14, 2016 3:06PM  3:18PM 
C18.00002: Multipolar effects in Eu2Ir2O7 Yilin Wang, Xi Dai We use the density functional theory plus the rotationally invariant HartreeFock meanfield method to study the magnetic properties of the pyrochlore iridate material Eu$_2$Ir$_2$O$_7$ (5d$^5$), where the crystal field splitting $\Delta$, spinorbit coupling (SOC) $\lambda$ and Coulomb interaction $U$ of Ir atoms are all playing significant roles. We have constructed a $t_{2g}$ Wannier tightbinding Hamiltonian and calculated the $U$$\lambda$ phase diagram, from which we find a very stable allin/allout antiferromagnetic ground state for moderate SOC (0.20.5 eV). In this magnetic state, except for the dipole moments, we also find considerable multipolar moments (octupole) and large nonlinear magnetic susceptibility. With strong enough SOC, the system reduces to a $j_{\text{eff}}=\frac{1}{2}$ single band Hubbard model, and the ground state changes to another antiferromagnetic configuration without multipolar moments. Our results indicate that the coexisting multipolar order is crucial to stabilize the allin/allout state and contributes a lot to the nonlinear magnetic susceptibility. [Preview Abstract] 
Monday, March 14, 2016 3:18PM  3:54PM 
C18.00003: Resonant Xray scattering studies of magnetic order and excitations in pyrochlore iridates. Invited Speaker: Desmond McMorrow The rareearth pyrochlore iridates (R$_{\mathrm{2}}$Ir$_{\mathrm{2}}$O$_{\mathrm{7}}$, R$=$rare earth) have been proposed to host a number of exotic electronic states as a consequence of the existence of strong spinorbit coupling of the Ir$^{\mathrm{4+}}$ ion in the presence of significant electron correlations. Of crucial importance to understanding whether any of these states can be realized in practice is to determine the effective lowenergy Hamiltonian describing the system. Here we report a comprehensive series of resonant Xray experiments, both elastic (REXS) and inelastic (RIXS), which reveal the nature of the magnetic order and excitations in single crystals of Sm$_{\mathrm{2}}$Ir$_{\mathrm{2}}$O$_{\mathrm{7\thinspace }}$and Nd$_{\mathrm{2}}$Ir$_{\mathrm{2}}$O$_{\mathrm{7}}$. [Preview Abstract] 

C18.00004: ABSTRACT WITHDRAWN 
Monday, March 14, 2016 4:06PM  4:18PM 
C18.00005: The interplay of ferromagnetic and antiferromagnetic exchanges in the the 3d5d transition metal oxides Sr2BIrO6 (B=Ni, Cu, Zn) Katharina Rolfs, Ekaterina Pomjakushina, Sandor Toth, Vladimir Pomjakushin, Kazimierz Conder In the field of strongly correlated electron systems significant attention has been drawn towards the study of compounds based on magnetic 4d and 5d transition metal (TM) oxides. The spin orbit coupling (SOC) within these systems becomes nonnegligible compared to the crystal field energies and leads to new exotic ground states, such as the Mott insulating state in Sr2IrO4. In order to understand the influence of the SOC on the electronic ground state the focus also turned to mixed 3d5d systems, which gives the possibility to disentangle SOC effects from common chargespinorbital physics, as it is present in pure 3d TMOs and could also introduce new properties. One group within these candidates is the group of Irbased double perovskites A2BIrO6 (B=3d TM). While in a large number of insulating 3d TMOs, the superexchange interactions between magnetic ions being nearest neighbour is adequate to determine the magnetic order, the SOC of 5d elements can change the exchange topology. This is possibly the case for Sr2NiIrO6, Sr2CuIrO6 and Sr2ZnIrO6. All compounds are high oxygen pressure compounds, which we successfully synthesised. The influence of the 3d metal on the magnetic properties will be discussed based on bulk magnetisation, transport measurements and neutron diffraction. [Preview Abstract] 
Monday, March 14, 2016 4:18PM  4:30PM 
C18.00006: Magnetic Orders Proximal to the Kitaev Limit in Frustrated Triangular Systems: Application to Ba$_3$IrTi$_2$O$_9$ Andrei Catuneanu, Jeffrey Rau, HeungSik Kim, HaeYoung Kee Frustrated transition metal compounds in which spinorbit coupling (SOC) and electron correlation work together have attracted much attention recently. In the case of 5$d$ transition metals, where SOC is large, $j_\text{eff}=1/2$ bands near the Fermi level are thought to encompass the essential physics of the material, potentially leading to a concrete realization of exotic magnetic phases such as the Kitaev spin liquid. We derive a spin model on a triangular lattice based on $j_\text{eff} = 1/2$ pseudospins that interact via antiferromagnetic Heisenberg ($J$) and Kitaev ($K$) exchanges, and crucially, an anisotropic $(\Gamma)$ exchange. Our classical analysis of the spin model reveals that, in addition to small regions of 120$^\circ$, $\mathbb{Z}_2$ / dual$\mathbb{Z}_2$ vortex crystal and nematic phases, the stripy and ferromagnetic phases dominate the $J$$K$$\Gamma$ phase diagram. We apply our model to the 5$d$ transition metal compound, Ba$_3$IrTi$_2$O$_9$, in which the Ir$^{4+}$ ions form layered twodimensional triangular lattices. By combining our abinitio and classical analyses, we predict that Ba$_3$IrTi$_2$O$_9$ has a stripy ordered magnetic ground state. [Preview Abstract] 
Monday, March 14, 2016 4:30PM  4:42PM 
C18.00007: SpinOrbit Induced Emergent Magnetic Phases in Iridium Based Oxides Indra Dasgupta We shall present our results on the electronic structure of 6H perovskite type quaternary iridates Ba$_{3}$MIr$_{2}$O$_{9}$, where Ir ions form structural dimers and non magnetic M provides a knob to tailor the valence of Ir. We shall first consider the d$^{4.5}$ insulator Ba$_{3}$YIr$_{2}$O$_{9}$ and explain the origin of the pressure induced magnetic transition to a spinorbital liquid (SOL) state in this system. As a next example [2], we shall consider a pentavalent (d$^{4}$) 6H perovskite iridate Ba$_{3}$ZnIr$_{2}$O$_{9}$ and argue that the ground state of this system is a realization of novel SOL state. Our results reveal that such a system provides a very close realization of the elusive J=0 state where Ir local moments are generated due to the comparable energy scales of the singlettriplet splitting driven by spinorbit coupling (SOC) and the superexchange interaction mediated by strong intradimer hopping, however substantial frustrated interdimer exchange interactions induce quantum fluctuations favoring SOL phase at low enough temperature. [1] S.K. Panda, S. Bhowal, Ying Li, S. Ganguly, Roser Valenti, L. Nordstrom, and I. Dasgupta Physical Review B (Rapid Communication), 2015 (Accepted for Publication), [2] A. Nag et. al. arXiv:1506.04312 [condmat.strel] [Preview Abstract] 
Monday, March 14, 2016 4:42PM  4:54PM 
C18.00008: Orbitalselective singlet dimer formation and suppression of double exchange in 4d and 5d systems Sergey Streltsov, Gang Cao, Daniel Khomskii One of the main mechanisms of ferromagnetic ordering in conducting materials is the double exchange (DE). It is usually supposed in DE model that the Hundâ€™s coupling $J_H$ is much larger than electron hopping $t$; in this case one stabilizes the state with maximum spin per pair of ions, which finally leads to ferromagnetism in bulk systems. We show that in the dimerized $4d/5d$ transition metal oxides for which $J_H$ is reduced and $t$ is in contrast enhanced, another situation is possible, when formation of the spinsinglets on delocalized orbitals is more favorable. This leads to suppression of the DE and to a strong decrease of the total spin. The model calculations using the dynamical meanfield theory show that this effect survives even in the extended systems, not only for dimers. Such a situation is realized, e.g., in Y$_5$Mo$_2$O$_{12}$, CrO$_2$ under pressure and in many other $4d/5d$ based materials. Another mechanism, which may suppress DE and which is also typical for $4d/5d$ compounds is the spinorbit coupling (SOC). We show on the example of Ba$_5$AlIr$_2$O$_{11}$, that in this system it is the combination of molecularorbital formation and SOC that strongly decreases magnetic moment on Ir. [Preview Abstract] 
Monday, March 14, 2016 4:54PM  5:06PM 
C18.00009: Investigation of frustrated antiferromagnet on the honeycomb lattice with an applied field Shenxiu Liu, Hongchen Jiang, Tom Devereaux Quantum spin1/2 honeycomb XY antiferromagnet, or the equivalent hardcore boson system, with both nearestneighbor J1 and nextnearestneighbor J2 interactions is a representative frustrated system possibly hosting new phases of matter. Recent theoretical study suggests that this system may exhibit a series of incompressible states, which host fermionic elementary excitations rather than bosonic excitations, at small fixed filling factors or equivalent magnetic field strength. In this work, we will examine the theoretical prediction by directly studying the frustrated honeycomb J1J2 XY model, using unbiased grand canonical densitymatrix renormalization group technique. By searching for magnetization plateaus with an applied magnetic field, we will ultimately determine the presence of these incompressible states as well as their properties. For a more comprehensive study, different variants of this model, including the honeycomb J1J2 Heisenberg antiferromagnet, will also be investigated. [Preview Abstract] 
Monday, March 14, 2016 5:06PM  5:18PM 
C18.00010: Topological magnon bands in pyrochlore iridate thin films Pontus Laurell, Gregory A Fiete Thin films of pyrochlore iridates (A$_2$Ir$_2$O$_7$) have previously been studied using weakcoupling techniques such as DFT and DMFT. Here we approach the systems from the strong coupling limit. Since the pyrochlore iridates most likely reside in the difficult to access intermediate coupling regime, a strong coupling study should offer a complementary viewpoint to existing studies. We carry out a variational mean field calculation of the magnetic ground state configurations. We show that the allin/allout state, known as the bulk ground state, is generically present in the triangularKagometriangular trilayers. This state can also be found in bilayer films, in specific parameter regimes. A linear spinwave analysis of the magnetic excitations is also carried out. It shows that when the magnetic order is in (or close to) the allin/allout state, the lowest magnon band acquires a nonzero Chern number, leading to the prediction that pyrochlore iridate thin films can host the magnon Hall effect. [Preview Abstract] 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2019 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700