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 H3LiIr2O6 Shuai Wang, Long Zhang, Fa Wang H3LiIr2O6 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 O-H-O "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 H3LiIr2O6 is a quantum spin liquid promoted by quantum paraelectricity. |
Thursday, March 7, 2019 2:42PM - 2:54PM |
V46.00002: RIXS studies of the low-energy magnetic excitations in double perovskite iridates La2BIrO6 (B=Co, Ni, Zn) Wentao Jin, Sae Hwan Chun, Jungho Kim, Diego M Casa, Choongjae Won, Kyungdong Lee, Namjung Hur, Young-June Kim Ordered double perovskite (DP) materials [1-3], A2BB'O6, 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 x-ray scattering (RIXS) measurements at Ir L3 edge, we have investigated the low-energy magnetic excitations in a series of La2BIrO6 single crystals, where B is Co, Ni and Zn, respectively. In La2CoIrO6 and La2NiIrO6, 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 La2ZnIrO6 in which the 3d ions are non-magnetic, suggesting the importance of 3d-5d hybridization in the magnetic properties of DP iridates. |
Thursday, March 7, 2019 2:54PM - 3:06PM |
V46.00003: Effect of charge doping in Os-based double perovskites with strong spin-orbit coupling Erick Garcia, Rong Cong, Phuong Tran, Patrick Woodward, Vesna F Mitrovic, Samuele Sanna The combined effects of strong electronic correlations and spin-orbit 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 Ba2NaOsO6, a double perovskite with strong SOC. Ba2NaOsO6 is a 5d1 Mott insulator that displays an exotic canted two-sublattice ferromagnetic state believed to be driven by the staggered quadrupolar order [L. Lu et al. Nature Comm. 2017], while Ba2CaOsO6 is a 5d2 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 Ba2Na1-xCaxOsO6 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 x-ray 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 x-ray 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 Ba5AlIr2O11 based on a two site Ir-Ir model and it directly confirms the existence of dimer orbital in this material. Second, we simulate the measured RIXS spectrum in Ba2YOsO6 based on an Anderson impurity model from a DFT+DMFT calculation, and based on this simulation we found that the energy scale of spin-orbit coupling (SOC) and Hund's coupling is comparable and the effective SOC effects in this 5d3 compound is still significant so that it cannot be described by a pure spin-3/2 state. |
Thursday, March 7, 2019 3:18PM - 3:30PM |
V46.00005: Interplay of novel magnetism and structural symmetry in Ba2NaOsO6 as a function of magnetic field and temperature revealed via resonant and non-resonant x-ray scattering Zahirul Islam, Kristin Willa, Ulrich Welp, Jacob P.C. Ruff, Zhu Diao, Andreas Rydh, Ritesh K. Das, Wai-Kwong Kwok, Ian R Fisher We studied correlation of lattice symmetry and magnetism in Ba2NaOsO6 (BNOO) showing that it was tetragonal (T) even at 300K, with a transition into an orthorhombic (O) phase near a "ferromagnetic" transition at Tc~6.9K . Fluctuations of O-phase seem to appear well above Tc, and calorimetric data, concurrently recorded with scattering, indicates a T-to-O transition at T>Tc. At T<Tc, 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 q-satellite along with its angular, polarization, and azimuthal properties of resonant scattering is indicative of a novel orbital-ordered phase with quantization (or principal) axis confined to the orthorhombic bc-plane. |
Thursday, March 7, 2019 3:30PM - 3:42PM |
V46.00006: Spin-orbit entanglement and j=1/2 state in CuAl2O4 Sergey Streltsov, Sergey Nikolaev, Igor Solovyev, Andrey Ignatenko, Santu Baidya, Valentin Irkhin, Daniel Khomskii, Je-Guen Park Spin-orbit (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 bond-dependent exchange interactions, as manifested in 4d and 5d systems. We show that a very similar situation can be realized in cuprates, when the Cu2+ ions reside in a tetrahedral environment. A special attention will be paid to CuAl2O4, which was experimentally found to retain cubic structure and does not show any long-range magnetic order down to T=0.5 K. These are the strong Coulomb correlations and the spin-orbit coupling, which conspire to suppress the Jahn-Teller distortions in CuAl2O4. The spin-orbit-entangled jeff=1/2 state is then naturally realizes in the situation of t2g5 configuration and degenerate t2g subshell. This in turn explains unusual magnetic properties of CuAl2O4. Using first-principles calculations, we construct a realistic spin model and show that the magnetic properties of this compound are largely controlled by anisotropic compass-type exchange interactions that dramatically modify the magnetic ground state by lifting the spiral spin-liquid degeneracy and stabilizing a commensurate single-q spiral. |
Thursday, March 7, 2019 3:42PM - 3:54PM |
V46.00007: Dirac Nodal Lines and Density-Functional Prediction of a Large Spin Hall Effect in 6H-perovskite Iridate Ba3TiIr2O9 Sayantika Bhowal, Sashi Sekhar Satpathy
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Thursday, March 7, 2019 3:54PM - 4:06PM |
V46.00008: Covalency-driven collapse of strong spin-orbit coupling in face-sharing iridium octahedra Mai Ye, Heung Sik Kim, Jae-Wook Kim, Choong-Jae Won, Kristjan Haule, David Vanderbilt, Sang-Wook Cheong, Girsh E Blumberg We report ab-initio density functional theory calculation and Raman scattering results to explore the electronic structure of Ba5CuIr3O12 single crystals. This insulating iridate, consisting of face-sharing IrO6 octahedra forming quasi-one-dimensional chains, cannot be described by the local jeff = 1/2 moment picture commonly adopted for discussing electronic and magnetic properties of iridate compounds with IrO6 octahedra. The shorter Ir-Ir distance in the face-sharing geometry, compared to corner- or edge-sharing 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 low-energy electronic degree of freedom. The theoretically predicted three-peak structure in the joint density of states, a distinct indication of deviation from thejeff = 1/2 picture, is verified by observing the three-peak structure in the electronic excitation spectrum by Raman scattering. |
Thursday, March 7, 2019 4:06PM - 4:18PM |
V46.00009: Spin-orbit coupled ground state of mixed valence iridate Ba5AlIr2O9 Vamshi Mohan Katukuri, Xingye Lu, Thorsten Schmitt, Oleg Yazyev Interplay of electronic correlations and spin-orbit interactions in Ir4+ and Ir5+ oxides results in insulating Jeff = 1/2 and Jeff = 0 ground states, respectively. By now, this has been well understood theoretically and established experimentally. However, in compounds where the dimerisation of Ir4+ and Ir5+ ions is structurally more favourable, the microscopic understanding of the local electronic structure is lacking. For example, a direct overlap of the Ir d-orbitals within the dimers may lead to significant bonding-antibonding splittings, which diminishes the role of spin-orbit mixing, considerably modifying the local electronic picture. With Ba5AlIr2O11 as an example, we show that the direct d-d hybridisation effects are relatively weak, while electronic correlations (configuration mixing) and spin-orbit coupling play a dominant role. Using a combination of ab initio many-body wave function quantum chemistry calculations and resonant inelastic X-ray scattering experiments, we elucidate the electronic structure of Ba5AlIr2O11. Our investigation shows that the two Ir ions (Ir4+ and Ir5+) in Ir2O9 dimer units preserve their local Jeff ground states close to 1/2 and 0, respectively. |
Thursday, March 7, 2019 4:18PM - 4:30PM |
V46.00010: Magnetic field tuning of non-reciprocal and achiral spin waves in antiferromagnetic Ba3NbFe3Si2O14 Chris Stock, Manila Songvilay, Jose A Rodriguez, Paolo G. Radaelli, Laurent Chapon, Sang-Wook 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 non-reciprocal spin waves in antiferromagnetic langasite Ba3NbFe3Si2O14 using neutron spectroscopy. Applying a time reversal symmetry breaking magnetic field that also breaks a two-fold 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 +/- μ0H. We discuss the scaling of this effect with field and suggest it microscopically originates from spin-orbit coupling mediated through antisymmetric exchange. |
Thursday, March 7, 2019 4:30PM - 4:42PM |
V46.00011: New insight into the low temperature phase of Ca3Ru2O7 Danilo Puggioni, James M Rondinelli Despite the countless theoretical studies on the Ruddlesden-Popper ruthenate Ca3Ru2O7, 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, spin-orbit interaction, and structural degrees of freedom are necessary to understand the properties of the low temperature phase of Ca3Ru2O7. |
Thursday, March 7, 2019 4:42PM - 4:54PM |
V46.00012: Electric Field-Tuned Electronic Structure Revealed by Time- and Angle-Resolved 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 angle-resolved photoemission spectroscopy (ARPES) experiment because the electric field will deflect the photoelectrons. Here I will present our experimental results on electric field-tunable electronic structure by using a new strategy which can obtain the transient electronic structure under a tunable electric field, based on time- and angle-resolved photoemission spectroscopy (TrARPES). |
Thursday, March 7, 2019 4:54PM - 5:06PM |
V46.00013: Low temperature thermal conductivity measurement of magnetic delafossite PdCrO2 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 PdCoO2 [2] but never in the magnetic partner compound PdCrO2. Here, we present such a study, down to sub-Kelvin 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 Sr1-xBaxMn1-yTiyO3 Kamal Chapagain, Bogdan Dabrowski, Omar Chmaissem, Stanislaw Kolesnik, Haumod Somali, Dennis Brown The structural and magnetic properties of unique single-ion manganese-based multiferroic perovskites Sr1-xBaxMn1-yTiyO3 (SBMTO) were investigated by XRD. For compounds near x = 0.45–0.65 and y = 0–0.1, a cubic to non-centrosymmetric 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 BaTiO3 have been observed with maximum estimated polarization of ~ 29 μC/cm2 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 spin-orbital entanglement in d8 Mott insulators: the case of a diamond lattice antiferromagnet Fei-Ye Li, Gang Chen Motivated by the recent activities on the Ni-based diamond lattice antiferromagnet NiRh2O4, we theoretically explore on a general ground the unique spin and orbital physics for the Ni2+ ions with a 3d8 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 Ni2+ ion with a partially filled upper t2g level and a fully filled lower eg level, the atomic spin-orbit coupling becomes active at the linear order and would favor a spin-orbital-entangled singlet with quenched local moments in the single-ion limit. Thus, the spin-orbital entanglement competes with the superexchange and could drive the system to a quantum critical point that separates the spin-orbital singlet and the magnetic order. We further explore the effects of magnetic field and uniaxial pressure. The non-trivial response to the magnetic field is intimately tied to the underlying spin-orbital 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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