Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session F39: 5d/4d Transition Metal Systems IFocus
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Sponsoring Units: DMP Chair: Matthew Brahlek, Oak Ridge National Laboratory Room: Room 231 |
Tuesday, March 7, 2023 8:00AM - 8:36AM |
F39.00001: Antiferromagnetic excitonic insulator state in Sr3Ir2O7 Invited Speaker: Mark P Dean Excitonic insulators are usually considered to form via the condensation of a soft charge mode of bound electron-hole pairs. This, however, presumes that the soft exciton is of spinsinglet character. Early theoretical considerations have also predicted a very distinct scenario, in which the condensation of magnetic excitons results in an antiferromagnetic excitonic insulator state. Here we report resonant inelastic x-ray scattering (RIXS) measurements of Sr3Ir2O7. By isolating the longitudinal component of the spectra, we identify a magnetic mode that is well-defined at the magnetic and structural Brillouin zone centers, but which merges with the electronic continuum in between these high symmetry points and which decays upon heating concurrent with a decrease in the material’s resistivity. We show that a bilayer Hubbard model, in which electron-hole pairs are bound by exchange interactions, consistently explains all the electronic and magnetic properties of Sr3Ir2O7 indicating that this material is a realization of the long-predicted antiferromagnetic excitonic insulator phase. |
Tuesday, March 7, 2023 8:36AM - 8:48AM |
F39.00002: Light-induced insulator-metal transition in Sr2IrO4 reveals the nature of the insulating ground state Dongsung Choi, Doron Azoury, Changming Yue, Jiyu Chen, Francesco Petocchi, Zachary Porter, Edoardo Baldini, Baiqing Lyu, Masataka Mogi, Yifan Su, Stephen D Wilson, Martin Eckstein, Philipp Werner, Nuh Gedik Proposed as a Jeff = 1/2 Mott insulator induced by strong spin-orbit coupling (SOC), Sr2IrO4 has been considered as an alternative material platform to explore the mechanism of high-Tc superconductivity, due to its structural and electronic similarities to high-Tc superconducting cuprates. While the Jeff = 1/2 ground state and the important role of SOC in the opening of the charge gap are experimentally confirmed, the Mott nature of the low-temperature insulating phase in Sr2IrO4 has not been firmly established. A Slater mechanism for the opening of the gap has been proposed in previous studies, but a general consensus has not been reached due to several counter evidences. Resolving this issue is however essential for understanding the similarities and differences between the cuprates and Sr2IrO4 and the fact that (high-Tc) superconductivity has not been observed in doped Sr2IrO4. Here, we report the observation of a gap-closing and the formation of weakly-renormalized electronic bands in the gap region as a result of a light-induced insulator-metal transition in Sr2IrO4, measured via time- and angle-resolved photoemission spectroscopy. Considering the typical temperature and doping evolution of Mott-gaps and Hubbard bands, we argue that these observations provide a clear evidence of the non-Mott nature of the insulating state. For the origin of the charge gap, we instead consider a correlated band insulator picture, where anti-ferromagnetic correlations play a key role in the opening of the gap. |
Tuesday, March 7, 2023 8:48AM - 9:00AM |
F39.00003: Strain-induced superconductivity in Sr2IrO4 Lena Engström, Chia-Chuan Liu, William Witczak-Krempa, Tami Pereg-Barnea The iridates offer a unique environment of strong interactions and spin-orbit coupling. Sr2IrO4 is a spin-orbit coupled antiferromagnet. Under electron doping it is predicted to have a, yet unconfirmed, superconducting order. However, the magnetism remains strong for chemical doping. We model compressive strain as an additional knob to tune correlations in this multi-orbital compound. The magnetism in Sr2IrO4 has been shown to be sensitive to the lattice geometry. As the lattice is modified by a compressive strain, magnetism is suppressed and the Fermi surface topology changes. By modelling a strain-dependent effective interaction via the random phase approximation, the found phase diagram under doping and strain has superconducting regions. A cuprate-like d-wave superconductivity is favored under strain. In addition, several multi-band orders can be favored when tuning the interaction parameters and band structure. Both an s+--wave and an odd parity order can be present. As the strain is increased the spin-orbit coupled nature of the compound comes into question as correlations in spin and pseudospin channels can compete. We discuss regimes where strain and doping are more likely to result in superconductivity. |
Tuesday, March 7, 2023 9:00AM - 9:12AM |
F39.00004: Proportionality between the magnetic exchange energy and Néel temperature in pyrochlore ruthenates Jae Hyuck Lee, Dirk Wulferding, Dongjoon Song, Junkyoung Kim, Seungryung Park, Changyoung Kim Pyrochlore oxides provide a rich platform for exploring diverse states of matter due to the unique crystal structure and chemical versatility. They are one of the most widely known systems to inherently host magnetic frustrations, setting the ground for exotic quantum states and diverse magnetic structures. Specifically, pyrochlore ruthenates, a family of strongly correlated 4d materials, houses a wide range of interaction between orbital, spin, and lattice degrees of freedom. Rare earth pyrochlore ruthenates are generally known to be spin-1 Mott insulators that display antiferromagnetic ordering of Ru ions below the Néel temperature (TN), with TN strongly depending on the size of the rare earth ions. Also, they have a linear relation between rare earth ionic radii, lattice constant, Ru-O-Ru bond angle, bond length, and Ru 4d t2g bandwidth which is believed to be the origin of the systematic metal to insulator transition shown throughout these compounds. |
Tuesday, March 7, 2023 9:12AM - 9:24AM |
F39.00005: Non-centrosymmetric Sr2IrO4 obtained under high pressure Haozhe Wang, Madalynn Marshall, Zhen Wang, Kemp Plumb, Martha Greenblatt, Yimei Zhu, David Walker, Weiwei Xie Sr2IrO4 with strong spin-orbit coupling (SOC) and Hubbard repulsion (U) hosts Mott insulating states. The similar crystal structure and electronic properties observed enhance its analogies to the high-Tc superconductive cuprates, La2CuO4 family. Here we report a non-centrosymmetric Sr2IrO4 phase (Sr2IrO4-HP) synthesized at 6 GPa and 1400 °C. Sr2IrO4-HP crystallizes into the tetragonal space group I4mm without an inversion center. The crystal structure and its non-centrosymmetric character were determined by single crystal X-ray diffraction (SCXRD) and high-resolution scanning transmission electron microscopy (HR-STEM). Our magnetic characterization indicates there is a significant suppression of Néel temperature to around 86 K, with a larger moment observed than ambient pressure Sr2IrO4. Moreover, the resistivity measurement suggests three-dimensional Mott variable-range hopping existed in the system. This non-centrosymmetric Sr2IrO4-HP appears to be a unique material to offer a further possible understanding of high-Tc superconductivity. |
Tuesday, March 7, 2023 9:24AM - 9:36AM |
F39.00006: Propagating Spin-Orbit Excitons in a Correlated Metal Valentin L Zimmermann, Lichen Wang, Arvind K Yogi, Huimei Liu, Deniz Wong, Christian Schulz, Maciej Bartkowiak, Klaus Habicht, Pascal Puphal, Masahiko Isobe, Matteo Minola, Giniyat Khaliullin, Bernhard Keimer, Matthias Hepting The presence of strong spin-orbit coupling (SOC) can lead to highly exotic phases of matter in quantum materials. While SOC is considered as a dominant energy scale in 5d compounds such as Sr2IrO4, its strength decreases for lighter elements and its significance in shaping the electronic structure of 4d materials is a topic of active debate. Here, we present a comprehensive study of the solid-solution Sr2Rh1-xIrxO4, which is situated between the 4d-electron metal Sr2RhO4 and the 5d-electron Mott insulator Sr2IrO4. We investigate the evolution of the low-energy electronic structure in the substitution series using resonant inelastic x-ray scattering and Raman spectroscopy. A focus of our study is Sr2RhO4, where we detect similar spin-orbit entangled excitations as previously observed in Sr2IrO4, albeit on a smaller energy scale and with an opposite dispersion, which we rationalize in terms of the distinct ground states of the two materials. Our findings shed new light on the role of SOC in 4d compounds and we comment on the prospects of using cation substitution as a platform to tune the effective spin-orbit interaction strength. |
Tuesday, March 7, 2023 9:36AM - 9:48AM |
F39.00007: Localization and delocalization in the layered phosphide EuCd2P2 Christopher C Homes, G.Lawrence Carr, Z.-C. Wang, Kyle Fruhling, Fazel Tafti The temperature dependence of the optical properties of EuCd2P2 have been determined over a wide frequency range for light polarized in the a-b planes. At room temperature, the low-energy optical conductivity reveals two infrared-active lattice modes, one weak and one strong, superimposed on a weak electronic background, with σ1(ω→0) ~30 Ω-1cm-1. The conductivity can be reproduced reasonably well using a Drude-Lorentz model, yielding an estimate for the Drude plasma frequency ωp,D ~1100 cm-1 and scattering rate 1/τD ~800 cm-1. At about 18 K, well above the magnetic transition at TN ~11 K, the free carriers become localized [1], likely due to the formation of ferromagnetic domains that result in spin-polarized clusters due to spin-carrier coupling [2]; however, below TN metallic behavior is recovered. We have attempted to map out these domains using an infrared microscope coupled to a synchrotron light source by studying the interaction of the high-frequency infrared mode with the electronic background. |
Tuesday, March 7, 2023 9:48AM - 10:00AM |
F39.00008: Spiral electronic structure of chiral crystal NbSi2 Cheng Zhang Recently, so-called chirality induced spin selectivity effect has been observed in the chiral crystal NbSi2 through electrical conductivity measurement [1,2]. To investigate the electronic structure of NbSi2, we performed synchrotron-radiation angle resolved photoemission spectroscopy for both right-(P6222) and left-handed (P6422) samples. Since the NbSi2 crystal is difficult to cleave, the clean surface was obtained by mechanical polishing, Ar ion sputtering and annealing. We found not only the clear energy bands, but also spiral-shaped constant energy contours at specific binding energies. The fact that the helicity of this pattern is reversed in the crystal having opposite chirality indicates that the observed intriguing pattern has its origin in the structural chirality. This result demonstrates that a photoemission experiment can be a new way to distinguish the chirality of crystals. Furthermore, in the presentation we will also discuss the possible origin of the spiral pattern based on the results of DFT calculations. |
Tuesday, March 7, 2023 10:00AM - 10:12AM |
F39.00009: Non-local electrodynamics in ReO3 Timothy Branch, Graham Baker, Mohamed Oudah, James Day, Alannah Hallas, Douglas A Bonn The metallic oxide ReO3 is known for its remarkably low residual resistivity, being the most highly conducting of all oxide materials[1]. Such resistivity endows ReO3 with an extremely long low-temperature electronic mean free path (MFP), comparable to the ultrapure delafossites. Recent microwave spectroscopy measurements of one such delafossite—PdCoO2—have revealed a directional anomalous skin effect response that depends on the orientation of its hexagonally-faceted Fermi surface[2]. As with the conventional anomalous skin effect, this response indicates that ballistic (non-local) transport effects are dominant. Recent models for the anomalous skin effect response also predict anisotropic responses in materials with cubic Fermi surface facets[3]. ReO3 is an ideal candidate material for investigating this phenomenology as some of its Fermi surfaces have cubic facets. Here we present microwave spectroscopy measurements of high-purity ReO3 at low temperatures. We compare these results to conventional skin effect responses and discuss how a faceted Fermi surface might contribute to novel behaviours in high-purity metals. |
Tuesday, March 7, 2023 10:12AM - 10:24AM |
F39.00010: Synthesis of Cage-structured Compounds for Thermoelectricity Nusrat Yasmin, Md. Fahel Bin Noor, Sarah Longworth, Tiglet Besara The ability to directly convert between heat and electricity makes thermoelectric materials appealing. The main issue is that the physical parameters used to determine thermoelectric performance work against one another. For achieving the optimum performance, hindering lattice vibration by forming cage structures in which heavy atoms can rattle is a plausible way. Millimeter-sized single crystals of AB2Zn20 compounds (A and B are transition metals or rare earth elements and reside within Zn cages) have been successfully grown with the Zn self-flux technique, including previously unknown 5th- and 6th-period transition metal-containing phases. Structural studies have been performed with x-ray diffraction and Raman spectroscopy, followed by magnetization measurements and thermoelectric characterizations. |
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