Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session B70: IridatesFocus Recordings Available
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Sponsoring Units: DMP Chair: Woojin Kim, Stanford University Room: Hyatt Regency Hotel -Jackson Park B |
Monday, March 14, 2022 11:30AM - 12:06PM |
B70.00001: Tuning magnetism with pressure in honeycomb and square lattice Iridates Invited Speaker: Daniel Haskel The connection between quantum spin liquids and possible routes to high Tc superconductivity and topological quantum computing has led to a flurry of activity aimed at generating and detecting these unusual quantum states. Realizing this elusive state of matter in real materials is challenging as it requires fine tuning of exchange (magnetic) interactions to drive a frustrated, dynamically disordered, magnetic state. Unlike chemical doping, applied pressure has the ability to tune interatomic distances and bond angles without adding structural disorder hence providing a unique pathway to balancing exchange interactions and stabilizing exotic magnetic states. Iridates with honeycomb- and square-lattice structures are potential candidates to host quantum spin liquid states, a result of strong spin-orbit coupling and/or large spatial extent of 5d orbitals. We summarize progress and challenges in our efforts to stabilize spin liquid states in honeycomb Li2IrO3 and square-lattice Sr2IrO4 under the application of external pressure. |
Monday, March 14, 2022 12:06PM - 12:18PM |
B70.00002: Complex phase diagram of the honeycomb iridate Cu2IrO3 Gilberto F Fabbris, Aidan Thorn, Wenli Bi, Mykola Abramchuk, Faranak Bahrami, Jungho Kim, Eduardo H Poldi, Mary Upton, Toru Shinmei, Tetsuo Irifune, Fazel Tafti, Aleksey Kolmogorov, Daniel Haskel The recently synthesized family of intercalated Jeff = 1/2 honeycomb iridates feature promising evidence for hosting the Kitaev quantum spin liquid state. Here, we explore the high-pressure phase diagram of the intercalated honeycomb Cu2IrO3 at room temperature and 15 K using x-ray scattering and spectroscopy, as well as ab initio evolutionary structure search1. Compression below 10 GPa drives a structural phase transition marked by the formation of Ir-Ir dimers that destroy the Jeff orbitals. A discontinuous reduction in interplanar distance occurs around 15 GPa and 30 GPa at room and low temperatures, respectively, but the resulting high-pressure diffraction patterns are markedly different. More importantly, the low temperature phase features a dramatic Cu to Ir electron transfer not seen at room temperature. The potential origins of such large electronic structure temperature dependence and the implications to other honeycomb iridates will be discussed. |
Monday, March 14, 2022 12:18PM - 12:30PM |
B70.00003: Response of local structure to electron doping and external magnetic field in CuIr2S4 Emil S Bozin, Robert Koch, Hechang Lei, Milinda Abeykoon, Cedomir Petrovic Thiospinel CuIr2S4 possessing partially filled iridium 5d t2g manifolds exhibits a metal to insulator transition around 230 K accompanied by orbital and charge order and spin singlet dimerization [1]. Local fluctuating orbital degeneracy lifting (ODL) state, a precursor to the transition, was recently discovered in its high temperature metallic regime [2]. By utilizing high energy X-ray total scattering measurements at National Synchrotron Light Source II, we explore temperature evolution of the dimerized and ODL states from the local structure perspective upon their perturbation by external stimuli. Specifically, we will discuss the effects of electron doping, achieved via Zn/Cu substitution of up to 70% including superconducting compositions [3], and application of magnetic field of up to 5 T, and the implications for the properties. |
Monday, March 14, 2022 12:30PM - 12:42PM |
B70.00004: Magnetic excitations in the highly frustrated fcc iridate K2IrCl6 Qiaochu Wang, Kemp Plumb Magnetic materials with a high degree of geometrical frustration are prime candidates to realize exotic ground states governed by quantum fluctuations. K2IrCl6 is a model antiferromagnet with Ir4+ on a face-centered cubic lattice which is an exciting compound to explore Heisenberg-Kitaev exchange physics. The combination of crystal field and spin-orbit coupling renders a half-filled band of Jeff=1/2 character, which is localized by even moderate electronic correlations.[1] This Jeff=1/2 state and 90° Ir-O-Ir superexchange pathway favor both Heisenberg and Kitaev exchange interactions. In this talk, I will discuss inelastic neutron scattering measurements on K2IrCl6 and quantify the magnetic excitation spectra with a model including nearest and next-nearest neighbor Heisenberg interactions, Kitaev exchange and off-diagonal anisotropy. These measurements are essential to determine the Hamiltonian and thus where the material lies on the J-K-Γ phase diagram. |
Monday, March 14, 2022 12:42PM - 12:54PM |
B70.00005: Time reversal and lattice symmetry breaking in Nd2Ir2O7 observed by Raman scattering spectroscopy Yuanyuan Xu, Jérémie Teyssier, Yiming Qiu, Takumi Ohtsuki, Satoru Nakatsuji, Dirk Van Der Marel, Natalia Drichko Many intriguing phenomena such as anomalous Hall effect, metal-insulator transition, and quadratic band touching, has been discovered in pyrochlore iridate family thanks to the interplay of spin orbit coupling, electron correlations, and magnetic frustration. Among them, Nd2Ir2O7 was suggested to be a promising candidate to realize Weyl semimetal state upon breaking of the time-reversal symmetry (TRS) due to all-in-all-out order of Ir moments. In this work, we present a comprehensive low-temperature Raman scattering study of Nd2Ir2O7 single crystals. Our polarized Raman spectra reveals an abruptly opening of a partial gap of 24 meV in Raman susceptibility below TN = 33 K, possibly due to the splitting of the quadratic band touching. TRS breaking was evidenced by the appearance of the one magnon excitations at 15 meV below TN. This magnon excitation hardens and broadens upon further cooling down to 10 K, when the Nd moments show strong magnetic correlations. The occurrence of a new magnetic peak at 32 meV below 7 K indicates the accomplishment of the Nd long-range magnetic order, while subtle changes in phonons point on a lattice distortion. These results suggest a proximity of Nd2Ir2O7 to the Weyl semimetal state between 33 and 10 K. |
Monday, March 14, 2022 12:54PM - 1:06PM |
B70.00006: Experimental signatures of versatile Weyl semimetal in pyrochlore iridate with spin-ice like magnetic orders Kentaro Ueda, Hiroaki Ishizuka, Markus Kriener, Denis Maryenko, Minoru Kawamura, Masashi Kawasaki, Yoshinori Tokura We report experimental signatures of topological transitions among the Weyl semimetal states of pyrochlore $\pio $, where the Kondo coupling between the Ir topological electrons and the spin-ice like orders of Pr moments plays a decisive role. |
Monday, March 14, 2022 1:06PM - 1:18PM |
B70.00007: Spin fluctuations and possible superconductivity from canting in Sr2IrO4 Lena Engström, Chia-Chuan Liu, William Witczak-Krempa, Tami Pereg-Barnea The perovskite iridates share much of the phenomenology of high Tc superconducting cuprates. Close to the fermi surface, the bands structure of the iridate Sr2IrO4 is mainly of a pseudospin J=1/2 character. In analogy to the cuprates, models for these bands predict a possible d-wave superconductivity. However, it is possible that inter-band hybridization may be important for determining the type and magnitude of possible pairing functions. Therefore, multiorbital models are key to understanding how possible superconducting regimes could become more accessible. |
Monday, March 14, 2022 1:18PM - 1:30PM |
B70.00008: Interplay of magnetic and structural phase transitions in the Mott insulator Sr2IrO4 Xiang Li, Scott Cooper, Anjana Krishnadas, Alberto De la Torre, Robin Perry, Felix Baumberger, Daniel M Silevitch, David Hsieh, Thomas F Rosenbaum, Yejun Feng The single-layered Ruddlesden-Popper iridate Sr2IrO4 hosts a Jeff =1/2 state and an ab-plane canted antiferromagnetic structure, making it a promising candidate for hosting a range of exotic states. Pseudospins arising from the strong spin-orbit coupling (SOC) at the Ir sites have non-negligible coupling with the lattice and may be responsible for a series of finely-balanced magnetic transitions. In particular, we report a pressure-driven spin-flip transition to c-axis aligned antiferromagnetic order at ~10 GPa under hydrostatic conditions, using optical Raman scattering measurements to reveal a concurrent first-order structural transition. The phonon anomalies we observe through temperature- and polarization-dependent measurements indicate that the new phase embraces strong phonon anharmonicity and/or enhanced directional negative thermal expansion. The findings underscore the delicate interplay between the SOC and lattice in 5d materials and provide insights for potential functionalities. |
Monday, March 14, 2022 1:30PM - 1:42PM |
B70.00009: Orthorhombic-distortion induced distinct interlayer magnetic order in the 5d Mott insulator Sr2IrO4 Sujan Shrestha, Maximilian Kroutloher, Menglin Zhu, Jiwoong Kim, Jinwoo Hwang, Jung Ho Kim, Jong Woo Kim, Ambrose Seo We report a distinct interlayer antiferromagnetic stacking order in Sr2IrO4 thin films when substantially large orthorhombic distortion (> 1.5%) is applied via biaxial lattice strain in Sr2IrO4/Ca3Ru2O7 heterostructures. The anisotropic biaxial strain lowers the crystal symmetry of Sr2IrO4 from tetragonal to orthorhombic, stabilizing the Jeff = ½ pseudospin moment direction via magnetic anisotropy while evoking the competition between interlayer exchange and pseudo-dipolar interactions. Using resonant X-ray magnetic scattering, we observed La2CuO4-like interlayer antiferromagnetic order where the magnetic moment is parallel to the elongated b-axis and its stacking pattern is inverted from that of the tetragonal Sr2IrO4 crystal. This interlayer stacking order is explained by the competition between interlayer interactions such that the nearest interlayer exchange interaction exceeds the interlayer pseudo-dipolar interaction. Our result suggests that anisotropic strain-induced orthorhombic distortion provides a delicate knob for tuning the long-range magnetic order and enhancing the magnetic quantum fluctuations in quasi-two-dimensional systems. |
Monday, March 14, 2022 1:42PM - 1:54PM |
B70.00010: Single crystal growth of iridates without platinum impurities Jimin Kim, Jinkwang Kim, Hoon Kim, Hyun Woo Kim, Hyeong Woo Suh, Jun Sung Kim, BJ Kim Iridates have attracted much interest in the last decade for their novel magnetism emerging in the limit of strong spin-orbit coupling and possible unconventional superconductivity. A standard for growing single crystalline iridate has been the flux method using a platinum crucible. In this talk, we show that this widely used method compromises the sample quality by inclusion of platinum impurities. We find that single crystals of Sr2IrO4 grown in iridium crucibles show remarkable differences in characterizations using Raman spectroscopy, resonant inelastic X-ray scattering, and resistivity measurements. In particular, our Raman spectra are free of previously unidentified A1g peaks of sizable magnitudes, which point to their defect origin creating in-gap states. This interpretation is supported by the much larger activation energy extracted from our resistivity data. While the platinum inclusion went unnoticed in the stoichiometric insulating phase for a long time, its effects can be much more detrimental to transport properties of doping-induced metallic states. Therefore, our result suggests using growth methods that avoid platinum impurities for exploration of possible superconducting phases in iridates. |
Monday, March 14, 2022 1:54PM - 2:06PM |
B70.00011: High-field low-energy spin dynamics in the Kitaev QSL Candidate α-RuCl3 Kiranmayi Dixit, Colin Sarkis, Barry Winn, David G Mandrus, Stephen E Nagler, Christian Balz, Paula Lampen-Kelly, Arnab Banerjee The observation of the half-integer thermal quantum Hall effect in α-RuCl3 in its field-induced quantum spin liquid state, at a magnetic field of 8 T has led to the debate on the presence of a chiral spin gap in this phase. We investigate the magnetic excitations in this material using Neutron Scattering experiments to investigate if there is a spin gap and pay special attention to the overall nature of the low-energy excitations resolved in the 4D momentum, energy as a function of the magnetic field to 13.5 T |
Monday, March 14, 2022 2:06PM - 2:18PM |
B70.00012: Emergence of a new magnetic state in Sr2IrO4 tunable by in situ B2g strain Shashi K Pandey, Han Zhang, Junyi Yang, Joshua J Sanchez, Zhaoyu Liu, Andrew F May, Jiun-Haw Chu, Jong Woo Kim, Philip J Ryan, Haidong Zhou, Jian Liu Due to the unique combination of electron correlation and spin-orbit coupling, Iridates have attracted great attention in recent years. A prominent example is Sr2IrO4 which is a quasi-two-dimensional Jeff =1/2 canted antiferromagnetic (AF) Mott insulator with a layered structure similar to the parent phase of high-Tc cuprates. However, unlike the S=1/2 moments of Cu ions, an interesting feature of the Jeff = 1/2 moments is that they can form significant inter-site quadrupoles that are highly sensitive to lattice distortion. The resulting magnetoelastic coupling leads to spontaneous B1g anisotropy when the AF order breaks the tetragonality. In our experiment, we compared the magnetic responses to in-situ B1g and B2g strains, which represent two orthogonal symmetry configurations. While the B1g strain efficiently detwins the spontaneous AF domains, we observed a new state that breaks the translational symmetry along the c-axis. Our model analysis shows that such an emergent state is driven by an unusual quartic interaction, which is competing with the B1g anisotropy and can be in situ tuned by the applied strain. |
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