Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session C54: IridatesFocus Live
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Sponsoring Units: DMP Chair: Weiwei Xie, Rutgers, The State University of New Jersey |
Monday, March 15, 2021 3:00PM - 3:12PM Live |
C54.00001: Freestanding Sr2IrO4 nanomembranes: structural and optical properties Sujan Shrestha, Matthew Coile, Menglin Zhu, Maryam Souri, Jiwoong Kim, Rina Pandey, Joe Brill, Jinwoo Hwang, Jong Woo Kim, Ambrose Seo We report the structural and optical properties of nanoscale freestanding Sr2IrO4 thin film fabricated using a sacrificial water-soluble Sr3Al2O6 layer. The coherent lattice structure, phonon modes, two-magnon Raman scattering, and optical absorption spectra of the freestanding Sr2IrO4 nanomembrane are analogous to those of the layered iridate epitaxial thin-films and single crystals. Remarkably, the 3-unit-cell-thick SrIrO3 interfacial layers alleviate the formation of antiphase boundaries at the Sr2IrO4/Sr3Al2O6 interface, resulting in structurally-robust freestanding thin-film. Our experimental results show that this freestanding thin-film approach of layered oxides can provide techniques for tuning or realizing unprecedented states beyond conventional thin film methods, suggesting a pathway in achieving two-dimensional layered oxides electronics. |
Monday, March 15, 2021 3:12PM - 3:24PM Live |
C54.00002: Magnetic field dependence of second-harmonic generation in Sr2IrO4 Kyle Seyler, Alberto De La Torre, Zach Porter, Eli A Zoghlin, Robert Polski, Mai Nguyen, Stevan Nadj-Perge, Stephen D Wilson, David Hsieh An anomalous optical second-harmonic generation (SHG) signal was previously reported in Sr2IrO4 and attributed to a hidden odd-parity bulk magnetic state. We investigated the SHG signal using magnetic-field-dependent SHG rotational anisotropy and wide-field SHG imaging combined with atomic force microscopy. We observe a two-fold rotational symmetry of the anomalous SHG signal as a function of in-plane magnetic field orientation that is associated with a crystallographic distortion. We also show a change in SHG signal across step edges that tracks the bulk antiferromagnetic stacking pattern. We will discuss the implications of these results for the origin of the anomalous SHG signal. |
Monday, March 15, 2021 3:24PM - 3:36PM Live |
C54.00003: Reinvestigation of the low temperature phase of the pyrochlore iridate Eu2Ir2O7 Danilo Puggioni, Peter Kissin, Xiaoran Liu, Jak Chakhalian, Richard Averitt, James M Rondinelli Magnetic pyrochlore iridates are a class of compounds where the competition between spin-orbit coupling and electronic correlation results in intriguing physical properties, such as metal-insulator transition and topological phases. Among them, Eu2Ir2O7 has been predicted to be a Weyl semimetal in its low temperature all-in-all-out magnetic phase; however, the experimental results are controversial. While transport experiments suggest an antiferromagnetic insulator, optical response reveals a Weyl semimetallic electronic structure. |
Monday, March 15, 2021 3:36PM - 3:48PM Live |
C54.00004: Decoupling of magnetic and transport properties in single-crystal Sr2Ir1-xFexO4 Bing Hu, Hengdi Zhao, Yu Zhang, Feng Ye, Gang Cao Sr2IrO4 is a spin-orbit-coupled insulator with a Neel temperature TN=240 K. Our investigation of structural, magnetic, transport and thermal properties of Sr2Ir1-xFexO4 with 0<x<0.34 reveals that substituting 3d Fe4+ (3d4) ions for 5d Ir4+ (5d5) ions (or hole doping) in Sr2IrO4 retains the native crystal structure but alters the physical properties in an unexpected manner. In particular, for light Fe doping (0 ≤x ≤ 0.14), the Neel temperature remains essentially unchanged but the electrical resistivity drops by five orders of magnitude, exhibiting a metallic behavior above 100 K. However, when the Fe doping level approaches 34% or x ~ 0.34 the magnetic order is eventually suppressed and the resistivity rises slightly but the insulating state is never recovered. Such unparalleled changes in magnetic and transport properties observed here indicate an unconventional correlation between spin and charge, raising questions of the role the antiferromagnetism plays in the iridates. The results will be discussed along with comparison drawn with Sr2Ir1-xCoxO4, in which both antiferromagnetic and insulating states readily diminish upon slight Co doping. |
Monday, March 15, 2021 3:48PM - 4:00PM Live |
C54.00005: Laser-Induced Transient Magnons in Sr3Ir2O7 Throughout the Brillouin Zone Daniel Mazzone, Derek J Meyers, Yue Cao, James. G. Vale, Cameron Dashwood, Youguo Shi, Andrew J. A. James, Neil J Robinson, Jiaqi Lin, Vivek Thampy, Yoshikazu Tanaka, Allan Johnson, Hu Miao, Ruitang Wang, Tadesse Assefa, Jung Ho Kim, Diego M Casa, Roman Mankowsky, Diling Zhu, Roberto Alonso-Mor, Sanghoon Song, Hasan Yavas, Tetsuo Katayama, Makina Yabashi, Yuya Kubota Although ultrafast manipulation of magnetism holds great promise for new physical phenomena and applications, targeting specific states is held back by our limited understanding of how magnetic correlations evolve on ultrafast timescales. Using ultrafast resonant inelastic x-ray scattering [1-3] we demonstrate that femtosecond laser pulses can excite transient magnons at large wavevectors in the gapped antiferromagnet Sr3Ir2O7, and that they persist for several picoseconds which is opposite to what is observed in the nearly gapless magnet Sr2IrO4 [1]. Our work suggests that materials with isotropic magnetic interactions are preferred to achieve rapid manipulation of magnetism. |
Monday, March 15, 2021 4:00PM - 4:36PM Live |
C54.00006: Capturing and controlling antiferromagnetic fluctuations of pseudospin-half square lattice in artificial layered iridate. Invited Speaker: Jian Liu Increasing attention has been paid to 5d transitional metal compounds due to the intriguing impacts of spin-orbit coupling (SOC) and the possibilities of obtaining unique emergent properties. However, as one of the most important systems, the square-lattice iridates that can be described by a pseudospin-half Hubbard model show remarkable similarities to the parent compound of weakly spin-orbit-coupled high-Tc cuprates. The hidden role of strong SOC for correlated pseudospin-half electrons remains elusive, partly because of the limited available compounds with the Ruddlesden-Popper structure. This material bottleneck can be overcome by synthesizing and tailoring pseudospin-half square lattices in artificial layered structures. I will discuss our recent investigation on artificial crystal Srn+mIrnTimO3n+3m synthesized as perovskite (SrIrO3)n/(SrTiO3)m superlattices, which not only replicate the magnetic state and excitations but also afford remarkable tunabilities beyond the Ruddlesden-Popper phases, demonstrating the extraordinary sensitivity of the pseudospin-half electron to the structural modulations implemented by design. In virtue of this structural control, we are able to realize toy-model systems where the SOC is utilized to capture the two-dimensional fluctuations predicted by the Mermin-Wagner theorem as a giant enhancement of the antiferromagnetic ordering temperature under uniform magnetic field. Emergent longitudinal spin fluctuations characteristics of the Slater-Mott crossover are also observed as positive anomalous magnetoresistance above the ordering temperature. The results showcase that the SOC of 5d electrons provides potent pathways to capture the physics underlying correlated systems. |
Monday, March 15, 2021 4:36PM - 4:48PM Live |
C54.00007: Theoretical study of strain and superconductivity in Sr2IrO4 Lena Engström, Tami Pereg-Barnea, William Witczak-Krempa Several parallels can be drawn between the perovskite iridate Sr2IrO4, and the high Tc cuprates. Although the low energy spectrum of Sr2IrO4 includes the three t2g bands, strong spin-orbit coupling splits the bands such that one can write an effective one-orbital J=1/2 model, in analogy with the single orbital of the cuprates. This has led to predictions of d-wave superconductivity in Sr2IrO4 upon doping. A three-orbital Hubbard model finds that the pairing is dependent on the interorbital interactions, therefore, an effective one orbital model may be insufficient in describing the superconducting state. In this work we investigate the multiorbital properties of Sr2IrO4, both with and without doping, under compressive epitaxial strain. Strain modifies lattice constants and bond orientations. It is modeled by modifying the orbital dependent hopping amplitudes and can therefore tune the orbital content of bands. By applying a multiple order parameter, self-consistent mean-field approach we study the magnetic structure and pairing symmetry of Sr2IrO4 under strain and carrier doping. We comment on ways to increase the chance of superconductivity. |
Monday, March 15, 2021 4:48PM - 5:00PM Live |
C54.00008: Bond directional anapole state in a spin-orbit coupled Mott insulator Sr2(Ir1−xRhx)O4 Hinako Murayama, Kousuke Ishida, Ryo Kurihara, takahiro ono, Yuki Sato, Yuichi Kasahara, Hikaru Watanabe, Youichi Yanase, Gang Cao, Yuta Mizukami, Takasada Shibauchi, Yuji Matsuda, Shigeru Kasahara In a spin-orbit coupled Mott insulator Sr2(Ir1−xRhx)O4, a possible hidden order phase has been reported distinctly above the Néel order phase, accompanying both inversion and time-reversal symmetry breakings. However, the nature of this mysterious phase remains largely elusive. We provide a detailed study of the hidden order phase through the combined study of in-plane magnetic torque and the nematic susceptibility measurements [1]. Our torque magnetometry provides thermodynamic evidence for an electronic nematic transition, breaking C4 rotational symmetry of the underlying lattice. However, in contrast to ordinal even-parity nematic orders, the nematic susceptibility exhibits no divergent behavior towards the onset of the hidden order. These results imply that the nematicity is not a primary order parameter but a secondary one of an odd-parity order parameter. Moreover, our results demonstrate that the hidden order phase is consistent with a bond directional anapole order, in which the intra-unit-cell loop current flows along only one of the diagonal directions in the IrO4 square. |
Monday, March 15, 2021 5:00PM - 5:12PM Live |
C54.00009: Quest for Quantum States via Field-Altering Technology Gang Cao, Hengdi Zhao, Bing Hu, Nick Pellatz, Dmitry Reznik, Pedro Schlottmann, Itamar Kimchi We report quantum phenomena in spin-orbit-coupled single crystals that are synthesized using an innovative technology that “field-alters” crystal via application of magnetic field during crystal growth. This work addresses a major challenge facing the research community today: A great deal of theoretical work predicting exotic states for strongly spin-orbit-coupled, correlated materials has thus far met very limited experimental confirmation. These conspicuous discrepancies are due chiefly to the extreme sensitivity of these materials to inherently existent structural distortions. The results presented in this talk demonstrate that the “field-altered” materials not only are much less distorted but also exhibit phenomena absent in their “non-altered” counterparts. The field-altered materials include an array of 4d and 5d transition metal oxides, and three representative materials presented in this talk are Ba4Ir3O10, Ca2RuO4, and Sr2IrO4. This study provides an entirely new paradigm for discovery of new quantum states and materials otherwise unavailable [1]. |
Monday, March 15, 2021 5:12PM - 5:24PM Live |
C54.00010: Thermal Conductivity and Thermoelectric Properties of the Spin-Orbit-Coupled Sr2IrO4 Yu Zhang, Ian Leahy, Hengdi Zhao, Bing Hu, Yifei Ni, Minhyea Lee, Gang Cao We report results of our recent study onpresent a comprehensive study on in-plane thermal conductivity and thermoelectric properties in high quality single crystals Sr2IrO4 with a Neel temperature at 240 K. We observe that the temperature dependence of thermal conductivity κ displays a sharp peak at around 10 K with its max value as high as 400 W/Km, yet little magnetic field dependence up to 14 T in all temperature from room temperature down to 4 K. This is in contrast to the Seebeck coefficient Sxx of which magnetic field dependence closely tracks that of the magnetization until its magnitude quenches to zero abruptly as temperature is lower below approximately 50 K. The new results of the thermal properties provide more insight into the physics of the iridate, especially spin degrees of freedom and phonons, which will be discussed along with other physical properties. |
Monday, March 15, 2021 5:24PM - 5:36PM Live |
C54.00011: Magnetic evolution in perovskite iridate Sr2IrO4 revealed by Raman scattering under pressure Xiang Li, Scott Cooper, Anjana Krishnadas, Alberto De La Torre, Felix Baumberger, Robin Perry, David Hsieh, Daniel Marc Silevitch, Thomas F Rosenbaum, Yejun Feng At ambient pressure, the spin-orbit coupling induced Mott insulator Sr2IrO4 shows canted antiferromagnetic (AFM) ordering with a Néel temperature of 240 K. The evolution of the magnetic structure with tuning parameters such as chemical doping and engineered strain has been well studied, but the behavior under hydrostatic pressure remains unsettled. Here, we present optical Raman measurements of low frequency magnons on Sr2IrO4 single crystals to investigate the complex magnetic evolution under high pressure. While at ambient pressure the Jeff=1/2 magnetic moments are mostly projected within the a-b plane, the spin correlation along the c-axis increases under pressure between layers. Starting approximately at 3 GPa, the AFM experience a spin-flop transition of first-order nature similar to the behavior in magnetic fields and of Sr3Ir2O7. The phase coexistence region extends to 11 GPa, before spins are fully rearranged from ordering in the basal plane to along the c-axis. Above 20 GPa, quasielastic Raman scattering arising from spin fluctuations appear, suggesting the onset of a disordered magnetic phase. |
Monday, March 15, 2021 5:36PM - 5:48PM Live |
C54.00012: Raman scattering and transport properties of vanadium-doped iridium dioxide nanowires grown via chemical vapor deposition Amanda Coughlin, Thomas Ruch, Xun Zhan, Tian Tong, Isaac Delgass, Brock Lehman, Hanyu Zhu, Jiming Bao, Shixiong Zhang Spin-orbit coupling (SOC) and electron interactions are two key ingredients for novel quantum phenomena and exotic topological states in condensed matter. 5d transition metal oxides (TMOs), such as the topological semimetal IrO2, possess strong SOC but relatively weak electron interaction. On the other hand, 3d TMOs, such as VO2, are strongly correlated systems in which SOC plays a negligible role. Integrating 3d and 5d transition metal elements into the same oxide compounds may offer a new platform to study the interplay of SOC and strong electron correlations. In this talk, we report on the synthesis of vanadium-doped IrO2 nanowires over a broad range of dopant concentrations grown via chemical vapor deposition. We will discuss how the electrical transport and structural properties of IrO2 vary as a function of vanadium doping, as well as how they are influenced by strain. |
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