Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session V46: 4d/5d Transition Metal Systems  New Phases 
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Sponsoring Units: DMP GMAG Chair: Jasminka Terzic, National High Magnetic Field Laboratory Room: BCEC 212 
Thursday, March 7, 2019 2:30PM  2:42PM 
V46.00001: Magnetic interactions and possible quantum paraelectricity in spin liquid candidate H_{3}LiIr_{2}O_{6} Shuai Wang, Long Zhang, Fa Wang H_{3}LiIr2O_{6} was recently synthesized and found to be potentially a quantum spin liquid. We studied the crystal structure and magnetic interactions of this material by first principles calculations, and further studied the resulting phase of the obtained pseudospin model by exact diagonalizations. We found that the dominant magnetic interaction of this material is ferromagnetic Kitaev interaction, but residue (further neighbor) Heisenberg interactions would still produce a zigzag magnetic order. We then studied the quantum effect of the hydrogen ions(protons), and found that the electric dipoles of OHO "hydrogen bonds" are disordered by strong quantum fluctuations. The electric dipole fluctuations can renormalize the magnetic interactions and potentially lead to a Kitaev spin liquid state in this material. We thus propose that H_{3}LiIr_{2}O_{6} is a quantum spin liquid promoted by quantum paraelectricity. 
Thursday, March 7, 2019 2:42PM  2:54PM 
V46.00002: RIXS studies of the lowenergy magnetic excitations in double perovskite iridates La_{2}BIrO_{6} (B=Co, Ni, Zn) Wentao Jin, Sae Hwan Chun, Jungho Kim, Diego M Casa, Choongjae Won, Kyungdong Lee, Namjung Hur, YoungJune Kim Ordered double perovskite (DP) materials [13], A_{2}BB'O_{6}, where B is a 3d and B' is a 4d or 5d transition metal ion, respectively, provide a rare opportunity to study the interaction between the intriguing magnetic behaviors of 5d systems and the better understood 3d magnetism, which is important for developing potential applications of these novel magnetic systems. Using resonant inelastic xray scattering (RIXS) measurements at Ir L_{3} edge, we have investigated the lowenergy magnetic excitations in a series of La_{2}BIrO_{6} single crystals, where B is Co, Ni and Zn, respectively. In La_{2}CoIrO_{6 }and La_{2}NiIrO_{6}, clear magnetic excitations with a large magnon gap ~ 40 meV were revealed, indicating an extremely large magnetic anisotropy in the magnetic interaction in these two compounds containing magnetic 3d ions. In contrast, the low energy magnon mode was absent in La_{2}ZnIrO_{6} in which the 3d ions are nonmagnetic, suggesting the importance of 3d5d hybridization in the magnetic properties of DP iridates. 
Thursday, March 7, 2019 2:54PM  3:06PM 
V46.00003: Effect of charge doping in Osbased double perovskites with strong spinorbit coupling Erick Garcia, Rong Cong, Phuong Tran, Patrick Woodward, Vesna F Mitrovic, Samuele Sanna The combined effects of strong electronic correlations and spinorbit coupling (SOC) leads to a plethora of emergent novel quantum states. However, predicting such emergent properties is complicated by the fact that spin is not a good quantum number in the presence of SOC. Therefore, experimental studies by local probes are highly sought to guide theoretical descriptions of this new physics. Double perovskite structures are particularly interesting cases of materials with such novel quantum states. Here, we investigate the effects of charge doping via the Na^{+}/Ca^{++} partial substitution on the magnetic ground state of Ba_{2}NaOsO_{6}, a double perovskite with strong SOC. Ba_{2}NaOsO_{6} is a 5d^{1} Mott insulator that displays an exotic canted twosublattice ferromagnetic state believed to be driven by the staggered quadrupolar order [L. Lu et al. Nature Comm. 2017], while Ba_{2}CaOsO_{6} is a 5d^{2} compound which displays an antiferromagnetic phase [C.M. Thompson et al. J. Phys. Cond. Matter 2014]. We present zero field μSR measurements on powder samples of the compound Ba_{2}Na_{1x}Ca_{x}OsO_{6} for 0 < x < 1 to investigate the interplay between spin, orbital, and charge degrees of freedom, which are believed to govern novel quantum states of compounds with strong SOC. 
Thursday, March 7, 2019 3:06PM  3:18PM 
V46.00004: EDRIXS: an open source toolkit for simulating resonant inelastic xray scattering spectrum based on exact diagonalization Yilin Wang, Xuerong Liu, Mark Dean, Gabriel Kotliar In this work, we present an open source toolkit called "EDRIXS" to simulate the resonant inelastic xray scattering (RIXS) spectrum based on exact diagonalization (ED) of a model Hamiltonian. It can deal with single atom, cluster models with the parameters being obtained by DFT+Wannier90 calculation, and Anderson impurity models obtained from a converged DFT+DMFT calculation. A very efficient parallel ED solver based on arpack library is implemented and RIXS spectrum is calculated by Krylov subspace technique. These key components are written by Fortran90 and a Python interface is designed to prepare the inputs and setup the calculations. We apply this toolkit to study two 5d materials. First, we perfectly reproduce the dimer excitations observed in the experimental RIXS spectrum of Ba_{5}AlIr_{2}O_{11} based on a two site IrIr model and it directly confirms the existence of dimer orbital in this material. Second, we simulate the measured RIXS spectrum in Ba_{2}YOsO_{6} based on an Anderson impurity model from a DFT+DMFT calculation, and based on this simulation we found that the energy scale of spinorbit coupling (SOC) and Hund's coupling is comparable and the effective SOC effects in this 5d^{3} compound is still significant so that it cannot be described by a pure spin3/2 state. 
Thursday, March 7, 2019 3:18PM  3:30PM 
V46.00005: Interplay of novel magnetism and structural symmetry in Ba_{2}NaOsO_{6} as a function of magnetic field and temperature revealed via resonant and nonresonant xray scattering Zahirul Islam, Kristin Willa, Ulrich Welp, Jacob P.C. Ruff, Zhu Diao, Andreas Rydh, Ritesh K. Das, WaiKwong Kwok, Ian R Fisher We studied correlation of lattice symmetry and magnetism in Ba_{2}NaOsO_{6} (BNOO) showing that it was tetragonal (T) even at 300K, with a transition into an orthorhombic (O) phase near a "ferromagnetic" transition at T_{c}~6.9K . Fluctuations of Ophase seem to appear well above T_{c}, and calorimetric data, concurrently recorded with scattering, indicates a TtoO transition at T>T_{c}. At T<T_{c}, a commensurate order at q=(1,0,0) (a is the shortest axis of O phase) is observed. In a magnetic field normal to q, this staggered order saturates, indicating a coherent rotation of ordered magnetic domains to align with field direction as well as revealing some qualitative differences with bulk M(H) data. Due to structural twins, bulk measurements are susceptible to effects of field applied along all three directions simultaneously, while scattering uniquely probes magnetic order within individual twins. This field evolution of qsatellite along with its angular, polarization, and azimuthal properties of resonant scattering is indicative of a novel orbitalordered phase with quantization (or principal) axis confined to the orthorhombic bcplane. 
Thursday, March 7, 2019 3:30PM  3:42PM 
V46.00006: Spinorbit entanglement and j=1/2 state in CuAl_{2}O_{4} Sergey Streltsov, Sergey Nikolaev, Igor Solovyev, Andrey Ignatenko, Santu Baidya, Valentin Irkhin, Daniel Khomskii, JeGuen Park Spinorbit (SO) Mott insulators are regarded as a new paradigm of magnetic materials, whose properties are largely influenced by the SO coupling and featured by highly anisotropic bonddependent exchange interactions, as manifested in 4d and 5d systems. We show that a very similar situation can be realized in cuprates, when the Cu^{2+} ions reside in a tetrahedral environment. A special attention will be paid to CuAl_{2}O_{4}, which was experimentally found to retain cubic structure and does not show any longrange magnetic order down to T=0.5 K. These are the strong Coulomb correlations and the spinorbit coupling, which conspire to suppress the JahnTeller distortions in CuAl_{2}O_{4}. The spinorbitentangled j_{eff}=1/2 state is then naturally realizes in the situation of t_{2g}^{5} configuration and degenerate t_{2g} subshell. This in turn explains unusual magnetic properties of CuAl_{2}O_{4}. Using firstprinciples calculations, we construct a realistic spin model and show that the magnetic properties of this compound are largely controlled by anisotropic compasstype exchange interactions that dramatically modify the magnetic ground state by lifting the spiral spinliquid degeneracy and stabilizing a commensurate singleq spiral. 
Thursday, March 7, 2019 3:42PM  3:54PM 
V46.00007: Dirac Nodal Lines and DensityFunctional Prediction of a Large Spin Hall Effect in 6Hperovskite Iridate Ba_{3}TiIr_{2}O_{9} Sayantika Bhowal, Sashi Sekhar Satpathy

Thursday, March 7, 2019 3:54PM  4:06PM 
V46.00008: Covalencydriven collapse of strong spinorbit coupling in facesharing iridium octahedra Mai Ye, Heung Sik Kim, JaeWook Kim, ChoongJae Won, Kristjan Haule, David Vanderbilt, SangWook Cheong, Girsh E Blumberg We report abinitio density functional theory calculation and Raman scattering results to explore the electronic structure of Ba_{5}CuIr_{3}O_{12} single crystals. This insulating iridate, consisting of facesharing IrO_{6} octahedra forming quasionedimensional chains, cannot be described by the local j_{eff }= 1/2 moment picture commonly adopted for discussing electronic and magnetic properties of iridate compounds with IrO_{6} octahedra. The shorter IrIr distance in the facesharing geometry, compared to corner or edgesharing structures, leads to strong covalency between neighboring Ir. Then this strong covalency results in the formation of molecular orbitals (MO) at each Ir trimers as the lowenergy electronic degree of freedom. The theoretically predicted threepeak structure in the joint density of states, a distinct indication of deviation from thej_{eff }= 1/2 picture, is verified by observing the threepeak structure in the electronic excitation spectrum by Raman scattering. 
Thursday, March 7, 2019 4:06PM  4:18PM 
V46.00009: Spinorbit coupled ground state of mixed valence iridate Ba_{5}AlIr_{2}O_{9} Vamshi Mohan Katukuri, Xingye Lu, Thorsten Schmitt, Oleg Yazyev Interplay of electronic correlations and spinorbit interactions in Ir^{4+} and Ir^{5+} oxides results in insulating J_{eff} = 1/2 and J_{eff} = 0 ground states, respectively. By now, this has been well understood theoretically and established experimentally. However, in compounds where the dimerisation of Ir^{4+} and Ir^{5+} ions is structurally more favourable, the microscopic understanding of the local electronic structure is lacking. For example, a direct overlap of the Ir dorbitals within the dimers may lead to significant bondingantibonding splittings, which diminishes the role of spinorbit mixing, considerably modifying the local electronic picture. With Ba_{5}AlIr_{2}O_{11} as an example, we show that the direct dd hybridisation effects are relatively weak, while electronic correlations (configuration mixing) and spinorbit coupling play a dominant role. Using a combination of ab initio manybody wave function quantum chemistry calculations and resonant inelastic Xray scattering experiments, we elucidate the electronic structure of Ba_{5}AlIr_{2}O_{11}. Our investigation shows that the two Ir ions (Ir^{4+} and Ir^{5+}) in Ir_{2}O_{9} dimer units preserve their local J_{eff} ground states close to 1/2 and 0, respectively. 
Thursday, March 7, 2019 4:18PM  4:30PM 
V46.00010: Magnetic field tuning of nonreciprocal and achiral spin waves in antiferromagnetic Ba_{3}NbFe_{3}Si_{2}O_{14} Chris Stock, Manila Songvilay, Jose A Rodriguez, Paolo G. Radaelli, Laurent Chapon, SangWook Cheong Reciprocity, in the context of optics and scattering, is defined as invariance when a source and detector are swapped indicating that the motion of an object in one direction being the same as that in the opposite. We investigate the magnetic field tuning of nonreciprocal spin waves in antiferromagnetic langasite Ba_{3}NbFe_{3}Si_{2}O_{14} using neutron spectroscopy. Applying a time reversal symmetry breaking magnetic field that also breaks a twofold symmetry of the underlying structure, different spin wave energies are observed when the sign is reversed for either the total momentum +/ Q=+/(G +/ q) or applied magnetic field +/ μ_{0}H. We discuss the scaling of this effect with field and suggest it microscopically originates from spinorbit coupling mediated through antisymmetric exchange. 
Thursday, March 7, 2019 4:30PM  4:42PM 
V46.00011: New insight into the low temperature phase of Ca_{3}Ru_{2}O_{7} Danilo Puggioni, James M Rondinelli Despite the countless theoretical studies on the RuddlesdenPopper ruthenate Ca_{3}Ru_{2}O_{7},_{ }the structure and physics of its low temperature phase (T < 48 K) remains unclear. Here, using first principle calculations, we shed light on this phase, reconciling several disparate experimental results with a model based on band theory and static correlations. Our results suggest that an accurate description of the strong interplay among electronic correlation, magnetic ordering, spinorbit interaction, and structural degrees of freedom are necessary to understand the properties of the low temperature phase of Ca_{3}Ru_{2}O_{7.} 
Thursday, March 7, 2019 4:42PM  4:54PM 
V46.00012: Electric FieldTuned Electronic Structure Revealed by Time and AngleResolved Photoemission Spectroscopy Shaohua Zhou, Changhua Bao, Yang Wu, Shuyun Zhou External electric field can easily modify the electronic structure of materials and create novel or useful quantum states. Such electric field tunable electronic structure is difficult to be probed by angleresolved photoemission spectroscopy (ARPES) experiment because the electric field will deflect the photoelectrons. Here I will present our experimental results on electric fieldtunable electronic structure by using a new strategy which can obtain the transient electronic structure under a tunable electric field, based on time and angleresolved photoemission spectroscopy (TrARPES). 
Thursday, March 7, 2019 4:54PM  5:06PM 
V46.00013: Low temperature thermal conductivity measurement of magnetic delafossite PdCrO_{2} Seita Onishi, Seunghyun Khim, Andrew Mackenzie, Elena Hassinger Ultrapure delafossite metals are remarkably distinct from conventional metal oxides with their high electrical conductivity (some even exceeding that of noble metals) [1]. Thermal conductivity has previously been studied in PdCoO_{2} [2] but never in the magnetic partner compound PdCrO_{2}. Here, we present such a study, down to subKelvin temperatures. The high conductivities of delafossites necessitate samples with high aspect ratios to reach low temperatures with a reliable temperature gradient and minimal sample heating. I will discuss how this was achieved in our experiments. 
Thursday, March 7, 2019 5:06PM  5:18PM 
V46.00014: Structural Study of the Multiferroics Perovskite Sr_{1x}Ba_{x}Mn_{1y}Ti_{y}O_{3} Kamal Chapagain, Bogdan Dabrowski, Omar Chmaissem, Stanislaw Kolesnik, Haumod Somali, Dennis Brown The structural and magnetic properties of unique singleion manganesebased multiferroic perovskites Sr_{1x}Ba_{x}Mn_{1y}Ti_{y}O_{3} (SBMTO) were investigated by XRD. For compounds near x = 0.45–0.65 and y = 0–0.1, a cubic to noncentrosymmetric tetragonal transition takes place below ~ 430 K on heating and at ~ 60 K lower temperature on cooling. Ferroelectric (FE) distortions c/a that are larger than the P4mm distortions of nonmagnetic BaTiO_{3} have been observed with maximum estimated polarization of ~ 29 μC/cm^{2} at ~ 220 K. At lower temperatures, the polarization is suppressed by ~ 40 % due to development of antiferromagnetic (AFM) phase, indicating very strong coupling between FE and AFM. The FE phase is rapidly suppressed by hydrostatic pressure. 
Thursday, March 7, 2019 5:18PM  5:30PM 
V46.00015: Emergent quantum criticality from spinorbital entanglement in d^{8} Mott insulators: the case of a diamond lattice antiferromagnet FeiYe Li, Gang Chen Motivated by the recent activities on the Nibased diamond lattice antiferromagnet NiRh_{2}O_{4}, we theoretically explore on a general ground the unique spin and orbital physics for the Ni^{2+} ions with a 3d^{8} electron configuration in the tetrahedral crystal field environment and on a diamond lattice Mott insulator. The superexchange interaction between the local moments usually favors magnetic orders. Due to the particular electron configuration of the Ni^{2+} ion with a partially filled upper t_{2g} level and a fully filled lower e_{g} level, the atomic spinorbit coupling becomes active at the linear order and would favor a spinorbitalentangled singlet with quenched local moments in the singleion limit. Thus, the spinorbital entanglement competes with the superexchange and could drive the system to a quantum critical point that separates the spinorbital singlet and the magnetic order. We further explore the effects of magnetic field and uniaxial pressure. The nontrivial response to the magnetic field is intimately tied to the underlying spinorbital structure of the local moments. We discuss the future experiments such as doping and pressure, and point out the general correspondence between different electron configurations under tetrahedral and octahedral crystal field environments. 
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