Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session A46: 4d/5d Transition Metal Systems -- Perovskite and Honeycomb IridatesFocus
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Sponsoring Units: DMP GMAG Chair: Feng Ye, Oak Ridge National Laboratory Room: BCEC 212 |
Monday, March 4, 2019 8:00AM - 8:36AM |
A46.00001: Anisotropic spin-orbit torque generation in epitaxial SrIrO3by symmetry design Invited Speaker: Tianxiang Nan Selected by Focus Topic Organizer (Gang Car and Jan Musfeldt) |
Monday, March 4, 2019 8:36AM - 8:48AM |
A46.00002: Electric Field Tuning of the Anomalous Hall Effect at the Oxide Interfaces: SrIrO3/SrMnO3 Sashi Sekhar Satpathy, Sayantika Bhowal
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Monday, March 4, 2019 8:48AM - 9:00AM |
A46.00003: Role of non-local correlations for spectral properties of Sr2IrO4 Benjamin Lenz, Cyril Martins, Silke Biermann The spin-orbit Mott insulator Sr2IrO4 has raised tremendous interest recently due to striking similarities to high-Tc superconducting copper oxides both in the pure and in electron-doped compounds. |
Monday, March 4, 2019 9:00AM - 9:12AM |
A46.00004: Broken in-plane rotational symmetry in the hidden order phase of Sr2Ir1-xRhxO4 Shigeru Kasahara, Ryo Kurihara, Hinako Murayama, Yuki Sato, Yuichi Kasahara, Yuji Matsuda, David Hsieh, Gang Cao The layered 5d transition metal oxide Sr2IrO4 hosts a Jeff =1/2 antiferromagnetic Mott insulating state, which strikingly resembles to the parent state of high-Tc cuprate superconductors. Recently, great interest has been aroused in the series of Sr2Ir1-xRhxO4, especially on the proposed hidden order phase above the antiferromagnetic ordering, which has been highlighted by optical second-harmonic generation and polarized neutron diffraction experiments [1, 2]. Here, by using exceptionally precise in-plane torque magnetometry [3-5], we provide thermodynamic evidence that nematicity, a spontaneous breaking of rotational symmetry of the underlying lattice, develops well above the antiferromagnetic transition in pure and doped Sr2Ir1-xRhxO4. Our highly sensitive magnetic anisotropy measurements under in-plane field rotation reveal the growth of two-fold oscillations, which onsets at the hidden order temperature T*. The present results demonstrate striking similarities between the hidden order phase in Sr2Ir1-xRhxO4 and the pseudogap phase in high-Tc cuprates. |
Monday, March 4, 2019 9:12AM - 9:24AM |
A46.00005: Ultrafast control of antiferromagnetism in a Mott insulator by photo-doping Alberto De la Torre, Gufeng Zhang, Michael Buchhold, Yuval Baum, Nicholas Laurita, John W Harter, Liuyan Zhao, Xiang Chen, Richard Douglas Averitt, Stephen Wilson, Gang Cao, Gil Refael, David Hsieh Ultrafast photo-doping provides a possible route to control antiferromagnetic order in Mott-Hubbard insulators out-of-equilibrium [1]. However, AFM order is notoriously challenging to probe by optical techniques [2]. Here, we demonstrate time-resolved nonlinear optical rotational anisotropy as a method to detect ultrafast transient changes of magnetic symmetry group. We leverage this technique to uncover the mechanisms by which photo-carriers suppress long range AFM order in the Mott insulator Sr2IrO4 and by which the AFM order is temporally restored. |
Monday, March 4, 2019 9:24AM - 9:36AM |
A46.00006: A time- and wavelength-resolved optical pump-probe reflectivity study of the Mott insulator Sr2IrO4 Isabelle Phinney, Alberto De la Torre, Xiang Chen, Stephen Wilson, David Hsieh Photo-induced charge excitations in the copper oxide based antiferromagnetic Mott insulators are able to decay on extremely fast timescales owing to strong spin-charge coupling effects [1]. In recent years, the photo-carrier dynamics of the antiferromagnetic Mott insulator Sr2IrO4 has also become a subject of intensive study [2-4] owing to its similarity to the cuprates in terms of structural, electronic and magnetic properties. Here we examine how the photo-carrier relaxation dynamics of Sr2IrO4 vary with different excitation densities and excitation wavelengths, which access different inter-band transitions, using time-resolved optical reflectivity measurements. We will discuss our results in comparison to the cuprates. |
Monday, March 4, 2019 9:36AM - 9:48AM |
A46.00007: ABSTRACT WITHDRAWN
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Monday, March 4, 2019 9:48AM - 10:00AM |
A46.00008: Symmetry-based analysis on Raman spectroscopy of two-magnon excitations in a spin-orbit coupled bilayer magnet Sr3Ir2O7 Siwen Li, Wencan Jin, Roberto D Merlin, Kai Sun, Zach Porter, Stephen Wilson, Liuyan Zhao Layered perovskite iridates have been shown to realize a rare Jeff= ½ Mott insulating antiferromagnetic ground state. While the magnetic excitation dispersion of the single layer perovskite iridate Sr2IrO4 can be well explained by a classical spin wave modelof an isotropic Heisenberg magnet, the bilayer counterpart Sr3Ir2O7 exhibits a giant magnetic excitation gap, ~90 meV, in the resonant inelastic X-ray scattering (RIXS) spectra whose origin is highly debated in literature. In this talk, we present our recent polarized Raman spectroscopy studies on magnetic excitations in Sr3Ir2O7. Two continuums associated with magnetic excitations are observed, one centering around 170 meV and the other around 100 meV that is close to the magnetic gap reported in RIXS spectra. Through Raman selection rule measurements, we observe that the ~100 meV feature only shows up in the symmetric A1g channel, while the ~170 meV one is present in both A1g and B2g channels. We show that both features originate from two-magnon excitations, by performing symmetry analysis on the spin waves of a bilayer magnet. Our result provides a new insight to the origin of “the giant magnetic gap” in RIXS spectra. |
Monday, March 4, 2019 10:00AM - 10:12AM |
A46.00009: Unusual magnetic fluctuations in the hidden order phase of Sr2(Ir,Rh)O4 Cheng Tan, Zhaofeng Ding, Jian Zhang, Lei Shu Recently, hidden order was obseved by L. Zhao et al. in Rhodium doped Sr2IrO4 at temperature TΩ. As in the pseudogap phase of high Tc cuprates, this order breaks rotational symmetry and time reversal symmetry, while preserving translational symmetry. Using muon spin relaxation (MuSR) measurement, we found two types of dynamic magnetic order with different fluctuation rates in the hidden order phase of Sr2(Ir,Rh)O4. We also found that the higher fluctuating magnetic field generated by the order setting in at the higher temperature slows its fluctuation rate on exiting the hidden order at TΩ. A bump appears in the relaxation rate around TΩ. The TΩ obtained by the MuSR measurements are condistent with those determined by second harmonic generation and polarized neutron scattering. |
Monday, March 4, 2019 10:12AM - 10:24AM |
A46.00010: Pseudospin-lattice coupling in the spin-orbit Mott insulator Sr2IrO4 Juan Porras, Joel Bertinshaw, Huimei Liu, Giniyat Khaliullin, Nakheon Sung, Jong-Woo Kim, Sonia Francoual, Paul Steffens, Guochu Deng, Marco Moretti Sala, Anna Efimenko, Ayman Said, Diego M Casa, Xian-Rong Huang, Thomas Gog, Jungho Kim, Bernhard Keimer, Bumjoon Kim Spin-orbit entangled magnetic dipoles, often referred to as pseudospins, provide a new avenue to explore novel magnetism inconceivable in the weak spin-orbit coupling limit, but the nature of their low-energy interactions remains to be understood. We present a comprehensive study of the static magnetism and low-energy pseudospin dynamics in the archetypal spin-orbit Mott insulator Sr2IrO4. We find that in order to understand even basic magnetization measurements, a formerly overlooked in-plane anisotropy is fundamental. In addition to magnetometry, we use neutron diffraction, inelastic neutron scattering and resonant elastic and inelastic x-ray scattering to identify and quantify the interactions that determine the global symmetry of the system and govern the linear responses of pseudospins to external magnetic fields and their low-energy dynamics. We find that a pseudospin-only Hamiltonian is insufficient for an accurate description of the magnetism in Sr2IrO4, and that pseudospin-lattice coupling is essential. This finding should be generally applicable to other pseudospin systems with sizable orbital moments sensitive to anisotropic crystalline environments. |
Monday, March 4, 2019 10:24AM - 10:36AM |
A46.00011: Bond ordering and phase transitions in Na2IrO3 under high pressure Zhimou Zhou, Kaige Hu, Yi-Wen Wei, Chao-Kai Li, Ji Feng The Kitaev model of spin-1/2 on a honeycomb lattice supports degenerate topological ground states and may be useful in topological quantum computation. Na2IrO3 with a honeycomb lattice of Ir ions has been extensively studied as a candidate for the realization of this model, due to the effective Jeff = 1/2 low-energy excitations produced by the spin-orbit and crystal-field effect. As the eventual realization of the Kitaev model has remained evasive, it is highly desirable and challenging to tune the candidate materials toward such an end. It is well known that external pressure often leads to dramatic changes in the geometric and electronic structure of materials. In this work, the high-pressure phase diagram of Na2IrO3 is examined by first-principles calculations. It is found that Na2IrO3 undergoes a sequence of structural and magnetic phase transitions, from a magnetically ordered phase with space group C2/m to two bond-ordered nonmagnetic phases. The low-energy excitations in these high-pressure phases can be well described by the Jeff = 1/2 states. |
Monday, March 4, 2019 10:36AM - 10:48AM |
A46.00012: Breakdown of magnetic order in the pressurized 3D Kitaev iridate β-Li2IrO3 Rudra Sekhar Manna, M Majumder, G. Simutis, Orain Jean Christophe, T. Dey, F. Freund, Anton Jesche, Rustem Khasanov, P. K. Biswas, E. Bykova, Natalia Dubrovinskaia, L. S. Dubrovinsky, R. Yadav, L. Hozoi, S. Nishimoto, Alexander Tsirlin, Philipp Gegenwart Novel electronic and magnetic properties are found in honeycomb lattice iridates, having dominant Kitaev interactions, due to the presence of strong spin-orbit coupling and electronic correlations. We present the measurements of magnetization, thermal expansion, magnetostriction, muon spin resonance, single crystal x-ray diffraction under hydrostatic pressure of 3D hyperhoneycomb β-Li2IrO3. These measurements are complemented by the ab initio calculations. The incommensurate magnetic order at 38 K initially increases as a function of hydrostatic pressure with a rate of 0.9 K/ GPa, consistent with the thermodynamic Ehrenfest relation. The partial polarization at 2.5 T decreases with increasing pressure signifies the instability of the magnetic order. The ordered state breaks down upon a first-order transition at around 1.4 GPa, giving way to a new ground state marked by the coexistence of dynamically correlated and frozen spins. This partial spin freezing may indicate the classical nature of the resulting pressure-induced spin-liquid, expected for large-Γ (nearest-neighbor off-diagonal exchange) limit [1]. |
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