Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session B46: 4d/5d Transition Metal Systems -- Ruthenates and RuCl3Focus
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Sponsoring Units: DMP GMAG Chair: Rongying Jin, Louisiana State University Room: BCEC 212 |
Monday, March 4, 2019 11:15AM - 11:51AM |
B46.00001: Exchange Interactions in Double Perovskite and Related Transition Metal Oxides Invited Speaker: Andy Christianson The double perovskite structure type is extremely flexible and accommodates a large fraction of the elements in the periodic table. Of particular interest are double perovskites containing magnetic 4d or 5d transition metal elements. Such materials exhibit novel phenomena including high ferrimagnetic transition temperatures in conjunction with half metallic or insulating behavior. One of the key remaining challenges is to accurately determine effective spin Hamiltonians to achieve a deeper understanding of this class of materials. This talk will focus on our efforts to determine the effective spin Hamiltonians with inelastic neutron scatting in materials including Sr2ScOsO6, Sr2FeOsO6, Sr2MgOsO6, Ca3LiOsO6, Ca3LiRuO6, and Ba2LaRuO6. Interestingly, all of the Osmates in the above list exhibit significant gaps in the magnetic excitation spectrum, despite being nominally in the 5d3 electronic configuration. This provides an indication of strong spin-orbit effects that would not normally be expected for a 5d3 half-filled t2g multiplet. We will also discuss what can be learned about the nature of the exchange interactions from inelastic neutron scatting on polycrystalline samples and how such experimental studies can be used to constrain models for effective spin Hamiltonians in double perovskites and related transition metal oxides. |
Monday, March 4, 2019 11:51AM - 12:03PM |
B46.00002: Metal Insulator Transitions, Strain and Electron-Lattice Coupling in Calcium Ruthenates Qiang Han, Rafael M Fernandes, Andrew Millis A general Ginzburg-Landau free energy is proposed for the metal-insulator transition (MIT) in correlated oxides, which incorporates magnetism, octahedral distortions, strain as well as the electronic transition. The theory is used to elucidate important experimental features observed across thermal-induced and current induced MIT in 2-1-4 and Ti-doped 3-2-7 calcium ruthenate compounds, including the coexistence of metallic and insulating domains, occurrence, orientation and lengths of stripes at the domain boundaries, as well as the impact of uniaxial and biaxial strain on the transition temperatures and elasto-resistance. Generalzation to MIT in other systems is presented. |
Monday, March 4, 2019 12:03PM - 12:15PM |
B46.00003: Resonant X-ray Scattering Study of Epitaxial Ca2RuO4 Thin Films Christopher Dietl, Joel Bertinshaw, Shyam Kanta Sinha, Georg Cristiani, Gennady Logvenov, Yury Khaydukov, Thomas Keller, Katrin Fürsich, Gideok Kim, Daniel Putzky, Laurence Bouchenoire, Joerg Strempfer, Sonia Francoual, Yongseong Choi, Peter Wochner, Shyjumon Ibrahimkutty, Peter van Aken, Bumjoon Kim, Bernhard Keimer We report a comprehensive study of epitaxial Ca2RuO4 thin films using resonant X-ray scattering at the Ru-L2 and L3 absorption edges, which directly probe the Ru 4d valence states. The strong modification of the electronic properties by biaxial strain is readily seen in transport measurements, which reveal a tuning from an insulator (on NdCaAlO4(110) substrates) to a metal (on LaSrAlO4(001)). Using magnetometry and resonant X-ray scattering, we can identify ferromagnetic phases in films on LaSrAlO4(001), LaSrAlO4(110) and LaAlO3(100) substrates and antiferromagnetic phases in films on NdCaAlO4(110), LaSrAlO4(110) and LaAlO3(100). The antiferromagnetic phases are most compatible with the B-Type magnetic structure found in the pressurized bulk system exhibiting a TN≈150 K. While the magnetic moment direction is typically along (010) in bulk Ca2RuO4, a polarization analysis of magnetic reflections of the film on NCAO(110) shows an unusual magnetic moment direction towards (-102). |
Monday, March 4, 2019 12:15PM - 12:27PM |
B46.00004: Investigation on the Itinerant/Local Magnetic Nature in SrRuO3 by ARPES Ji Seop Oh, Se Young Park, Wonshik Kyung, Naoki Kikugawa, Yoshiyuki Yoshida, Junyoung Kwon, Simon K Moser, Roland Koch, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, Changyoung Kim, Tae Won Noh SrRuO3 (SRO), one of the most famous perovskite metallic ferromagnets, has been the center of various research perspectives. One of the key issue with a long-time standing debate is the origin of ferromagnetism with metallicity. We studied the three-dimensional electronic structure of SRO single crystals by angle-resolved photoemission spectroscopy. We determined the inner potential of SRO single crystals for the first time. We also measured band dispersions on high symmetry planes and opened a way to cross-check theoretical electronic structures of SRO, which has not been accomplished during last 20 years. We also obtained temperature dependence of the ferromagnetic exchange splitting. These results implied the existence of short-range magnetic order above the Curie temperature and supported the dual nature of itinerant/local magnetism in SRO. Detailed experimental results and analyses will be presented and discussed. |
Monday, March 4, 2019 12:27PM - 12:39PM |
B46.00005: Magnetic susceptibility in the Hund's metal Sr2RuO4 from the dynamical two-particle vertex Hugo Strand, Manuel Zingl, Nils Wentzell, Olivier Parcollet, Antoine Georges Strontium Ruthenate (Sr2RuO4) is a strongly correlated complex oxide for which crystals with exquisite purity can be prepared, allowing for a wealth of experimental studies. It displays unconventional superconductivity, Hund's metal physics, and an incommensurate anti-ferromagnetic spin response. |
Monday, March 4, 2019 12:39PM - 12:51PM |
B46.00006: Hall number sign changes in Sr2RuO4 reveal coherent-to-incoherent and elastic-to-inelastic crossovers Manuel Zingl, Jernej Mravlje, Markus Aichhorn, Olivier Parcollet, Antoine Georges The 4d transition metal oxide Sr2RuO4 exhibits an unusual temperature dependence of its Hall number with two sign reversals: it is negative at low temperature below 30K (Fermi liquid temperature), turns positive, reaches a maximum and turns negative again at ~120K. We show that this non-monotonic behavior is due to the strong temperature-dependence of the ratio of inelastic scattering rates between the xy and xz/yz orbitals. This ratio becomes remarkably large upon cooling into the Fermi liquid regime, but is overshadowed at lower temperatures by impurity scattering. Another pivotal factor to account for the full temperature dependence is the spin-orbit coupling, as it impacts the topography of the Fermi surface sheets and strongly mixes their orbital character. By considering all these effects, we are able to reveal the significance of both sign changes: the one at 30K is a direct consequence of the crossover from elastic to inelastic scattering, while the higher-T one is associated with the coherence-to-incoherence crossover due to electronic correlations. These qualitative conclusions are supported by quantitative calculations using a Boltzmann transport theory in combination with dynamical mean-field theory, taking into account the electronic structure of the material. |
Monday, March 4, 2019 12:51PM - 1:03PM |
B46.00007: Electric field driven octahedral rotation in Sr2RuO4 and its underlying mechanism Wonshik Kyung, Choong Hyun Kim, Yeong Kwan Kim, Beomyoung Kim, Chul Kim, Woobin Jung, Junyoung Kwon, Minsoo Kim, Aaron Bostwick, Jonathan Denlinger, Yoshiyuki Yoshida, Changyoung Kim One of the key goals in the research of perovskite transition metal oxides (TMOs) is to design and control their physical properties, for which MO6 (M=transition metal) octahedron rotation (OR) is considered to be one of the key control parameters. We show, through a combined study of angle resolved photoemission, low energy electron diffraction and first-principles calculations, that OR can be induced and thus be tuned with electric field in Sr2RuO4. Originally rotated octahedra in the surface layer of Sr2RuO4 are restored to the bulk structure upon K dosing on the surface. Our theoretical investigation shows that OR in Sr2RuO4 originates from surface electric field which can be controlled via the screening effect of the overlaid K layer and that the variation of Sr-Sr vertical distance is responsible for the coupling between OR and electric field. Our finding raises a possibility for electric field control of physical properties through the variation of the OR angle even for non-piezoelectric materials. |
Monday, March 4, 2019 1:03PM - 1:15PM |
B46.00008: Quantum continuum fluctuations in glassy perovskite Ca(Co0.15Ru0.85)O3 Deepak K Singh, Yiyao Chen, Ashutosh Dahal, Jose A Rodriguez, Guangyong Xu, Thomas Heitmann, Vitalii Dugaev, Arthur Ernst The quantum spin continuum and classical spin freezing, associated with a glassy state, represent two opposite extremes of a correlated electronic material. Here, we report the coexistence of a quantum spin continuum with a weak spin glass order in Co-doped CaRuO3 perovskite near the chemical doping dependent metal-insulator transition boundary. Inelastic neutron measurements on Ca(Co0.15Ru0.85)O3 at low temperature, T = 1.5 K, reveal a continuum spectrum in the Q-E space due to uncorrelated spin fluctuations. This persists across the glass transition at TG~23 K. Furthermore, scaling of the dynamic susceptibility yields a very small scaling coefficient α~ 0.1, suggesting extreme locality of the dynamic properties. The experimental results indicate the realization of a narrow regime where the distinction between continuum dynamic behavior and glass-like regimes is reduced. |
Monday, March 4, 2019 1:15PM - 1:27PM |
B46.00009: Direct evidence of orbital-selective confinement effect of Ru 4d orbitals in SrRuO3 ultrathin film Soonmin Kang, Yi Tseng, Beom Hyun Kim, Seokhwan Yun, Byungmin Sohn, Bongju Kim, Daniel McNally, Eugenio Paris, Choong Hyun Kim, Changyoung Kim, Tae Won Noh, Sumio Ishihara, Schmitt Thorsten, Je-Guen Park The electronic structure of SrRuO3 thin film with the thickness from 50 to 1 unit cell (u.c.) is investigated via the resonant inelastic x-ray scattering (RIXS) technique at the O K-edge to unravel the intriguing interplay of orbital and charge degrees of freedom. We found that orbital-selective quantum confinement effect (QCE) induces the splitting of peaks in RIXS spectra of thin films, which corresponds to the charge transfer from O 2p to Ru 4d orbitals. At the same time, we observed a spectral weight transfer from electron-hole continuum to intersite d-d excitation across the metal-to-insulator transition (MIT) occurring between 5 and 4 u.c. samples. From these two clear observations, we conclude that QCE gives rise to a Mott insulating phase in ultrathin SrRuO3 films. Our interpretation of the RIXS spectra is supported by configuration interaction calculations of RuO6 cluster models. |
Monday, March 4, 2019 1:27PM - 1:39PM |
B46.00010: Substitution of 4d magnetic ions of a Kitaev-Heisenberg magnet by 3d magnetic ions: the case of Ru1-xCrxCl3 Gaël Bastien, Maria Roslova, Mohammad Hossein Haghighi, Kavita Mehlawat, Konstantin Nenkov, Jens Hunger, Anna Isaeva, Matthias Vojta, Thomas Doert, Anja Wolter, Bernd Büchner The Jeff=1/2 Mott insulator alpha-RuCl3 is a promising candidate for the realization of the Kitaev-Heisenberg model. It harbors an antiferromagnetic ground state below TN=7K, however, this ordered state can be suppressed by a magnetic field through a quantum critical point toward a possible quantum spin liquid [1]. In this study, the Ru3+ ions with Jeff=1/2 moments were partially substituted by Cr3+ ions with S=3/2. The effect of this substitution on the magnetic interactions, the magnetic ground state and the field-induced quantum spin liquid were studied by means of magnetization, ac susceptibility and specific heat measurements. The ground state of Ru1-xCrxCl3 was found to be a spin glass on a broad Cr concentration range with a maximum of the freezing temperature around x=0.5. Moreover, the evolution of the magnetic anisotropy with the substitution reveals a rather complex nature of the magnetic interaction between the Ru and Cr magnetic moments. |
Monday, March 4, 2019 1:39PM - 1:51PM |
B46.00011: Lattice symmetry breaking effects on the Raman phonon spectra of Kitaev magnet α-RuCl3 Thuc Mai, Amber McCreary, Paige Lampen-Kelley, Jeffrey Simpson, Stephen Nagler, David Mandrus, Angela Hight Walker, Rolando Valdes Aguilar The honeycomb lattice of α-RuCl3 is a potential candidate to study the Kitaev model. The predicted ground state for such a model is a Quantum Spin Liquid. There is significant interest in studying the Kitaev interaction in α-RuCl3, which orders antiferromagnetically below 6 K. Within a single layer, the honeycomb lattice exhibits a small distortion in the b direction, causing the symmetry to be reduced from hexagonal to orthorhombic. The possible effects of this broken in-plane honeycomb symmetry on the Kitaev interactions are not well understood. To this end, we utilize Raman spectroscopy to study the distortion by identifying splittings of the phonon modes. The polarization-resolved phonon spectra of α-RuCl3 as a function of the crystal orientation, both with the polarization parallel and perpendicular to the quasi-honeycomb plane will be described. Subtle shifts in the phonon peak frequencies were observed as a function of the orientation angle that can be explained by the distortion. A combination of group theory analysis and Laue X-ray diffraction were performed to determine the symmetry of each phonon mode. This methodology uniquely confirms that the point group of α-RuCl3 is 2/m. |
Monday, March 4, 2019 1:51PM - 2:03PM |
B46.00012: An effective spin Hamiltonian for α-RuCl3 and finite temperature properties Pontus Laurell, Casey Eichstaedt, Yi Zhang, Tom Berlijn, Adolfo German Eguiluz, Youhei Yamaji, Satoshi Okamoto We study the magnetic interactions in the Kitaev spin-liquid candidate α-RuCl3 using ab initio, exact diagonalization, and thermal pure quantum state methods. First we derive a new effective Hamiltonian, using an ab initio downfolding scheme based on a density functional theory calculation for the monoclinic crystal structure (space group C2/m). The calculation includes local crystal field splitting, and local and non-local spin-orbit coupling. Both local and nonlocal Coulomb interactions are computed using the constrained RPA method, and the interaction parameters for the effective spin Hamiltonian are determined using second order perturbation theory. We report both zero and finite temperature properties for this and previously proposed models, including dynamical spin structure factors and the specific heat. Our results highlight the importance of further range anisotropic spin-spin interactions, both for producing the zigzag magnetic order and for predictions beyond static properties at zero temperature. |
Monday, March 4, 2019 2:03PM - 2:15PM |
B46.00013: Electronic transport in thin crystals of transition metal oxides with Heisenberg-Kitaev physics Josue Rodriguez, Amirari Diego, Nicholas Breznay, Robert Kealhofer, Gilbert Lopez, David Rosser, Francisco Ramirez, Naomy Marrufo, Samantha Crouch, James G. Analytis, Claudia Ojeda-Aristizabal Josue Rodriguez, Amirari Diego, Gilbert Lopez, Nicholas P. Breznay, Robert Kealhofer, David Rosser, Francisco Ramirez, Naomy Marrufo, Samantha Crouch, James G. Analytis and Claudia Ojeda-Aristizabal |
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