Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P61: Spin-orbit coupled systemsFocus
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Sponsoring Units: DMP DCMP Chair: Matthias Vojta Room: Mile High Ballroom 4B |
Wednesday, March 4, 2020 2:30PM - 2:42PM |
P61.00001: Valence bond glass state in the 4d1 Mo5+ fcc antiferromagnet Ba2LuMoO6 Otto Mustonen, Heather Mutch, Peter Baker, Helen Walker, Charlotte Pughe, Fiona Coomer, Cheng Liu, Sian E Dutton, Edmund J Cussen Ba2LuMoO6 is a 4d1 Mo5+ fcc antiferromagnet in the double perovskite structure. Here we show that it is a valence bond glass; similar to the well known isostructural Ba2YMoO6 compound. Muon spin rotation and relaxation measurements on Ba2LuMoO6 revealed the lack of magnetic order or spin freezing down to 60 mK, in contrast to Ba2YMoO6 where spin freezing occurs at 1 K. Inelastic neutron scattering measurements revealed a singlet-triplet gap of 28 meV similar to Ba2YMoO6. These results are interpeted as the formation of a valence bond glass, where spin singlets form in a disorganized manner. Some orphan spin do not form singlets and remain paramagnetic even at 60 mK. |
Wednesday, March 4, 2020 2:42PM - 2:54PM |
P61.00002: Tuning electron correlation strength by charge doping of 5d1 double perovskites Erick Garcia, Paola Caterina Forino, Rong Cong, Charles Snider, Phuong Tran, Patrick Woodward, Vesna F Mitrovic, Samuele Sanna Competing interactions between spin-orbit coupling (SOC) and strong electron correlations have recently led to widespread studies of various emergent novel quantum phases. Double perovskites, particularly those containing 5d transition metal ions, present a useful opportunity to study such interactions since they display comparable magnitudes of electron correlations, crystal field, and SOC. Here, we present a systematic study of the electron doped powder Mott insulator Ba2Na1-xCaxOsO6 through the Na/Ca partial substitution using 23Na nuclear magnetic resonance at various doping concentrations. These results complement our previous muon spin relaxation (μSR) and superconducting quantum interference device (SQUID) measurements. Ba2Na1-xCaxOsO6 displays a crossover from an exotic canted ferromagnetic state driven by multipolar ordering at x = 0 to an antiferromagnetic state at x = 1. Moreover, the magnetic transition increases monotonically from 5 K to 40 K with increasing Ca concentration. The experimental results will be compared to theoretical work and their implications will be discussed. |
Wednesday, March 4, 2020 2:54PM - 3:06PM |
P61.00003: NMR study on single crystal Ba2LiOsO6 Charles Snider, Rong Cong, Erick Garcia, Samuele Sanna, Sanath Ramakrishna, Arneil P Reyes, Jiaqiang Yan, Vesna F Mitrovic Nuclear magnetic resonance (NMR) measurements on single crystals of Ba2LiOsO6 were carried out to test the universality of theoretical models based on anisotropic exchange interactions [1]. The results are compared with NMR findings on its isostructural and isovalent compound Ba2NaOsO6. Ba2LiOsO6 displays significant line broadening at low temperature, but no well-defined line splitting like its Na counterpart [2]. In addition, the spin-lattice relaxation and linewidth of its spectrum undergoes an abrupt change at 6 T. The implications of these findings will be discussed. |
Wednesday, March 4, 2020 3:06PM - 3:18PM |
P61.00004: On the charge transfer energy in iridates: a hard x-ray photoelectron spectroscopy study Daisuke Takegami, Deepa Kasinathan, Klaus Wolff, Simone G Altendorf, Chun-Fu Chang, Katharina Hoefer, Anna Meléndez-Sans, Yuki Utsumi, Federico Meneghin, Thai Duy Ha, Chien-Han Yen, Kai Chen, Chang-Yang Kuo, Y. F. Liao, Ku-Ding Tsuei, Ryan Morrow, Sabine Wurmehl, B.E. Prasad, Martin Jansen, Alexander Komarek, Philipp Hansmann, Liu Hao Tjeng We have investigated the electronic structure of iridates in the double perovskite crystal structure containing either Ir4+ or Ir5+ using hard x-ray photoelectron spectroscopy (HAXPES). The experimental valence band spectra can be well reproduced using tight binding calculations including only the Ir 5d, O 2p and O 2s orbitals with parameters based on the down-folding of the density-functional band structure results. We found that regardless the A and B cations, the A2BIrO6 iridates have essentially zero O 2p to Ir 5d charge transfer energies. They are extremely covalent systems with the consequence is that the magnetic exchange interactions become very long-ranged, thereby hampering the materialization of the Kitaev model. Nevertheless, it still would be possible to realize a spin-liquid system using the iridates with a proper tuning of the various competing exchange interactions . |
Wednesday, March 4, 2020 3:18PM - 3:30PM |
P61.00005: Monte Carlo simulation of a strong SOC model for d1 double perovskite Rong Cong, John Bradley Marston, Vesna F Mitrovic Recent NMR experiments have revealed exotic quantum phases in the magnetic Mott insulator with strong spin orbit coupling (SOC) Ba2NaOsO6[1]. To investigate the possible spin and orbital order patterns consistent with the NMR observations, we performed Monte Carlo simulations of a microscopic model for d1 double perovskites magnetic Mott insulators with multipolar spin interactions[2] . We obtained the low temperature phase diagram involving both spin and orbital degrees of freedom by magnetic annealing. We found that the zero temperature phase diagram consists of a fluctuating xyAFM, a canted FM[100] and a magnetic quadrupolar state each with distinct corresponding orbital ordering pattern. Furthermore, the xyAFM and the quadrupolar state are also found at intermediate temperatures as a result of enhanced thermal fluctuations. We demonstrate that the ground state evolves from the canted FM[100] state to the quadrupolar state as electric quadrupole-quadrupole interaction increases. |
Wednesday, March 4, 2020 3:30PM - 3:42PM |
P61.00006: Ground state in the novel dimer iridate Ba13Ir6O30 with Ir6+(5d3) Ions Hengdi Zhao, Feng Ye, Hao Zheng, Bing Hu, Yifei Ni, Yu Zhang, Itamar Kimchi, Gang Cao We have synthesized and studied a new iridate, Ba13Ir6O30, with unusual Ir oxidation states: 2/3 Ir6+(5d3) ions and 1/3 Ir5+(5d4) ions. Its crystal structure features dimers of face-sharing IrO6 octahedra, and IrO6 monomers, that are linked via long, zigzag Ir-O-Ba-O-Ir pathways. Nevertheless, Ba13Ir6O30 exhibits two transitions at TN1 = 4.7 K and TN2 = 1.6 K. This magnetic order is accompanied by a huge Sommerfeld coefficient 200 mJ/mole K below TN2, signaling a coexisting frustrated/disordered state persisting down to at least 0.05 K. This iridate hosts unusually large Jeff=3/2 degrees of freedom, which is enabled by strong spin-orbit interactions (SOI) in the monomers with Ir6+ ions and a joint effect of molecular orbitals and SOI in the dimers occupied by Ir5+ and Ir6+ ions. Features displayed by the magnetization and heat capacity suggest that the combination of covalency, SOI and large effective spins leads to highly frustrated ferrimagnetic ordering, a novelty of this new high-spin iridate. |
Wednesday, March 4, 2020 3:42PM - 4:18PM |
P61.00007: Spin-orbital-entangled quantum magnet on a honeycomb lattice Invited Speaker: Tomohiro Takayama In heavy transition-metal compounds containing 4d or 5d elements, strong spin-orbit coupling often yields spin-orbital-entangled Jeff-states for d-electrons. The magnetic interactions between such states may give rise to an exotic ground state due to their bond-sensitive character. In particular, quantum liquid state of spin-orbital-entangled objects have been expected to emerge in a simple honeycomb lattice. |
Wednesday, March 4, 2020 4:18PM - 4:30PM |
P61.00008: Jahn-Teller effect and spin-orbit coupling in t2g systems Sergey Streltsov, Daniel Khomskii In this talk we will discuss a very general problem of interplay between the Jahn-Teller (JT) effect and the spin-orbit coupling (SOC). It will be shown that the result of competition strongly depends on the specific situation: for some cases, such as d4 and d5, but also d2 configurations, strong SOC may sometimes reverse, but finally completely suppresses JT distortion, whereas in other cases, notably d3, SOC generates JT effect in the configuration which is usually considered as “orbitally dead”. |
Wednesday, March 4, 2020 4:30PM - 4:42PM |
P61.00009: Thermodynamics of Spin-Orbital Coupled Magnets: The Case of Dimers and Timers Stephen Winter, Ying Li, Roser Valenti Recently, there has been great interest in 4d and 5d magnetic insulators with strong spin-orbit coupling (SOC) - which have shown the potential to realise low-energy spin Hamiltonians featuring a variety of complex anisotropic couplings of fundamental interest. In this contribution, we focus on the theoretical description of recently reported spin-liquid candidate materials based on mixed valence M2O9 dimers [1] and M3O12 trimers [2,3]. The challenge of modelling these materials lies in their complex local electronic structures, which should manifest in e.g. complex spin-orbital ground states, instabilities towards charge order, and strong structural sensitivity of the magnetic response. We focus, in particular, on experimental signatures and consequences of various possible ground states as a function of SOC strength and electronic filling. Of particular experimental importance is the inapplicability of Curie-Weiss analysis due to the non-commutability of SOC with magnetic fields. |
Wednesday, March 4, 2020 4:42PM - 5:18PM |
P61.00010: Effect of disorder in Kitaev materials Invited Speaker: Natalia Perkins Recent years have seen remarkable progress in identifying candidate materials that can realize Kitaev quantum spin liquid [1]. In particular, a significant experimental and theoretical effort has been devoted to the study of magnetic properties of 4d and 5d systems, such as iridates and ruthenates, in which the interplay of strong spin-orbit coupling and electronic correlations gives rise to highly anisotropic and spatially dependent Ising-like interactions between effective moments J=1/2. Many of these materials show the presence of various forms of disorder, such as site disorder (magnetic or non-magnetic impurities), bond disorder and layer stacking faults. This is why these systems offer a remarkable playground for new phenomena that can be realized as a cooperative manifestation of disordered topological condensed matter systems. Recently we argued [2] that a minimal model of a bond disordered Kitaev quantum spin liquid can account for most of the salient experimental findings in H3LiIr2O6 [3]. However, other implications of disorder might be crucial to account for all observations in this material. Here we discuss how include vacancies in this consideration and consider combined effect of bond disorder and vacances at finite temperature properties of the Kitaev quantum spin liquid. |
Wednesday, March 4, 2020 5:18PM - 5:30PM |
P61.00011: Resonant elastic x-ray scattering on the molecular orbital in Li2RuO3 Seokhwan Yun, Beom Hyun Kim, Ki Hoon Lee, Dan G. Porter, Sergio Di Matteo, Soonmin Kang, Jaehong Jeong, alessandro bombardi, Je-Guen Park In solid, the d-orbital electrons of transition metal (TM) elements are generally described in the atomic orbital limit because an overlap between adjacent orbitals is much smaller than other perturbations like d-p hybridization or Coulomb U. However, when ionic radii increase with the rise of periodicity or adjacent ions are getting closer like ones in edge-sharing or face-sharing octahedra, the enhanced overlap of orbitals can lead the molecular behavior of orbital clusters. |
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