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 N56: Quantum Spin Liquid Materials III: Kitaev MaterialsFocus
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Sponsoring Units: GMAG Chair: Andrej Zorko, Jožef Stefan Institute Room: Room 304 |
Wednesday, March 8, 2023 11:30AM - 12:06PM |
N56.00001: A topological bosonic thermal Hall effect in Kitaev magnet α-RuCl3 Invited Speaker: Peter A Czajka α-RuCl3 is the most well-studied material candidate for realizing Kitaev’s honeycomb model. However, unlike the idealized model, the system has a complex magnetic phase diagram where a quantum spin liquid phase is thought to be realized at intermediate magnetic fields (7 < B < 12 T). Its thermal transport physics is similarly rich with various anomalous behaviors appearing in both the longitudinal (κxx) and Hall (κxy) conductivity channels. Our experiments have revealed magnetooscillations in κxx that are strikingly reminiscent of Shubnikov-de Haas oscillations in metals. This is highly unexpected as α-RuCl3 is strongly electrically insulating. We also observe a strongly temperature-dependent planar thermal Hall conductivity (κxy/T). The latter effect is well-described by topological bosonic excitations inherent to the high field spin-polarized phase rather than the Majorana fermions suggested by other groups. We quantitatively demonstrate that the excitations responsible for this planar thermal Hall effect are the same excitations studied in earlier spectroscopic measurements. The relation between this observation and the low temperature κxx oscillations and alleged half-integer quantized κxy/T will be discussed. |
Wednesday, March 8, 2023 12:06PM - 12:18PM Author not Attending |
N56.00002: Anisotropy in the low-energy excitations in α-RuCl3 with the applied field direction Kiranmayi Dixit, Stephen E Nagler, Barry Winn, Christian Balz, Colin Sarkis, Paula Lampen-Kelly, David G Mandrus, Jiaqiang Yan, Arnab Banerjee The in-plane direction of the applied magnetic field is expected to influence the low-energy excitations in the proximate Kitaev quantum spin liquid candidate α-RuCl3. We investigate these excitations using neutron scattering experiments to probe their overall nature resolved both in momentum and energy space and the topological spin gap expected in this material for two in-plane field directions. |
Wednesday, March 8, 2023 12:18PM - 12:30PM |
N56.00003: Field dependent specific heat measurements of the Kitaev quantum spin liquid candidate Na2Co2TeO6 shengjie fang, Kumpei Imamura, Ryuichi Namba, Kota Ishihara, Yuta Mizukami, Kenichiro Hashimoto, Takasada Shibauchi The Kitaev quantum spin liquid has attracted much attention because the ground state is exactly solvable, and its elementary excitations can be described by Majorana quasiparticles. The candidates have been recently suggested for honeycomb magnets with 3d electrons such as cobalt-based materials. Recent studies of the layered honeycomb magnet Na2Co2TeO6 with 3d electrons have shown that the antiferromagnetic phase is suppressed by an in-plane magnetic field application and changes to a spin-disorder phase above 7.5 T. Whether this field-induced spin-disorder phase is a Kitaev spin liquid or not is an unresolved issue in condensed-matter physics. |
Wednesday, March 8, 2023 12:30PM - 12:42PM |
N56.00004: Chemical tuning of a honeycomb magnet through a critical point Austin M Ferrenti, Maxime A Siegler, Shreenanda Ghosh, Hector Vivanco, Nina Kintop, Chris J Lygouras, Thomas J Halloran, Sebastian Klemenz, Collin L Broholm, Natalia Drichko, Tyrel M McQueen BaCo2(AsO4)2, or BCAO, has seen extensive study since its initial identification as a proximate Kitaev quantum spin liquid (KQSL) candidate. Although recent studies suggest its magnetic ground state is better described by the highly anisotropic XXZ-J1-J3 model, the ease with which magnetic order is suppressed with the application of a small in-plane magnetic field indicates proximity to a spin liquid phase. Upon chemical tuning via partial arsenic substitution with vanadium, BaCo2(AsO4)2-2x(VO4)2x, we show an initial suppression of long-range order in the BCAO system to T = 2.58 K, followed by the introduction of increased spin freezing at higher substitution levels. Between these two regions at x = 0.10, the system is shown via AC and DC susceptibility, Raman scattering spectroscopy, and heat capacity measurements to pass through a critical point where no phase transition is apparent down to T = 0.40 K. At this level of substitution, the competing nearest-neighbor J1 and third nearest-neighbor J3 interactions apparently become more balanced, producing a more complex magnetic ground state, likely stabilized by quantum fluctuations. This study shows how slight compositional change in magnetically-frustrated materials may be leveraged to enhance ground-state degeneracy and potentially realize a quantum spin liquid state. |
Wednesday, March 8, 2023 12:42PM - 12:54PM |
N56.00005: Resolving the origin of planar thermal Hall effect in the Kitaev magnet α-RuCl3 by field-angle-resolved specific heat measurements Kumpei Imamura, Yuta Mizukami, Yusei Yoshida, Kenichiro Hasshimoto, Nobuyuki Kurita, Hidekazu Tanaka, Satoshi Fujimoto, Masahiko G Yamada, Yuji Matsuda, Eun-Gook Moon, Takasada Shibauchi Recent experiments have shown that the layered honeycomb material α-RuCl3 exhibits several anomalous features that are consistent with expectations of the Kitaev quantum spin liquid (KQSL) when a magnetic field is applied in the honeycomb plane. Most remarkably, finite planar thermal Hall conductivity has been observed, whose magnitude is close to the half-integer quantization value expected for the chiral edge currents of Majorana fermions. However, there are attempts to offer a different explanation by the bosonic edge excitations due to topological magnons. A key to distinguishing between fermionic and bosonic origins of unusual features in the high-field state of α-RuCl3 is the difference in the field angle dependence of the excitation gap. The Majorana gap in the KQSL is expected to become zero for the field along the Ru-Ru bond direction (b-axis). This is in stark contrast to the bosonic case; the magnon gap remains finite even for the field along the b-axis where the topological chiral edge current changes sign. Here we study low-energy excitations in the high-field phase of α-RuCl3. Using a two-axis rotator, we measured field-angle-resolved specific heat C at very low temperatures down to ∼ 250 mK. When the field is aligned to the b-axis, we resolve finite residual C/T2 in the zero-temperature limit. This indicates the gapless linear energy dispersion (Dirac cone) of Majorana fermions in the field-induced KQSL state. |
Wednesday, March 8, 2023 12:54PM - 1:06PM |
N56.00006: Sample Dependence in Structure and Magnetism of α-RuCl3 Subin Kim, Young-June Kim, Ezekiel Horsley, Jacob Ruff In this talk, we report our study on sample dependence in characterizations and structure of Kitaev candidate material, α-RuCl3. Previously, sample dependence in Neel temperature was observed with different magnetic structural periodicity [1]. Such difference in structural periodicity can naturally arise from stacking fault and samples with Tn=7K were associate with high qualities. However, even high-quality samples with Tn=7K can have varying Tn between Tn=6.5K to Tn=7.5K. |
Wednesday, March 8, 2023 1:06PM - 1:18PM |
N56.00007: Transition signatures in the magnetothermal conductivity of α-RuCl3 Etienne Lefrancois We report measurements of the thermal conductivity κxx in the Kitaev spin liquid candidate α-RuCl3, performed on high-quality single crystals as a function of magnetic field B applied within the plane, for directions B || a and B || b, at temperatures down to 0.1 K. |
Wednesday, March 8, 2023 1:18PM - 1:30PM |
N56.00008: Planar Thermal Hall Effects in Kitaev Spin Liquid Candidate Na2Co2TeO6 Hikaru Takeda, Jiancong Mai, Masatoshi Akazawa, Kyo Tamura, Jian Yan, Kalimuthu Moovendaran, Kalaivanan Raju, Raman Sankar, Kwang-Yong Choi, Minoru Yamashita The Co-based honeycomb antiferromagnet Na2Co2TeO6 has attracted attention as a new Kitaev quantum spin liquid (KQSL) candidate, because it shows a field-induced phase transition from an antiferromagnetic to a spin disordered phase similar to the major candidate of KQSL, α-RuCl3. In this presentation, we present the experimental results of our thermal transport measurements on Na2Co2TeO6. A finite thermal Hall conductivity is resolved in the antiferromagnetic phase below the Néel temperature of 27 K under the magnetic fields applied in the ab plane. The temperature dependence of this planar Hall conductivity suggests the emergence of topological bosonic excitations. The field dependence of the Hall conductivity shows sign reversals at the critical fields in the AFM phase, suggesting the changes in the Chern number distribution of the topological magnons. Remarkably, a finite Hall conductivity is observed in the field applied along the a* axis, which is prohibited in a disordered state by the two-fold rotation symmetry around the a* axis of the honeycomb lattice, showing the presence of a magnetically ordered state that breaks the two-fold rotation symmetry. Our results demonstrate the presence of topological magnons in this compound in the whole field range below the saturation field. |
Wednesday, March 8, 2023 1:30PM - 1:42PM |
N56.00009: Combinatorial exploration of herbertsmithite-related quantum spin liquid candidates Alex Hallett, Catalina Avarvarei, John W Harter Geometric frustration of magnetic ions can lead to a quantum spin liquid (QSL) ground state, where long range magnetic order is avoided despite strong exchange interactions. The highly degenerate ground state that results can give rise to exotic properties, and the physical realization of QSLs comprises a major unresolved area of contemporary condensed matter physics. One such magnetically frustrated structure is the kagome lattice. Herbertsmithite [ZnCu3(OH)6Cl2] and Zn-barlowite [ZnCu3(OH)6BrF] feature pristine kagome layers of copper ions, and display experimental signatures of a QSL state at low temperatures. To investigate other possible QSL candidates, we perform a systematic first-principles combinatorial exploration of structurally related compounds [ACu3(OH)6B2 and ACu3(OH)6BC] by substituting cations A (with Ba, Be, Ca, Cd, Ge, Hg, Mg, Pb, Sn, Sr, and Zn) and anions B/C (with Br, Cl, F, and I). After optimizing such structures using density functional theory, we compare structural and thermodynamic parameters to determine which compounds are likely to host QSL phases. Pseudo-convex hull calculations using binary compounds are performed to determine feasibility of synthesis. We also estimate the likelihood of interlayer substitutional disorder and spontaneous distortions of the kagome layers. After considering all of these factors, we select promising candidate members of the herbertsmithite and Zn-barlowite families that may host QSL ground states and merit further attention. |
Wednesday, March 8, 2023 1:42PM - 1:54PM |
N56.00010: Scaling Behavior and Spin Fluctuations in BCAO Revealed by Thermal Transport Jiayi Hu Ever since the proposal of Kitaev model to realize quantum spin liquid, there have been many promising candidates. BaCo2(AsO4)2 is one of the materials in the latest generations. Since its magnetic ordering can be suppressed by a critical field as low as 0.5T, it's believed to possess a Kitaev term that's prominent among the physics at play. By probing with thermal transport techniques, we are able to extract information about its underlying spin interactions. In particular, we observed an intriguing scaling behavior of its highly field-sensitive thermal conductivity. The measurements also show magnetocaloric effect in Kxx and hysteresis in Kxy, which reveal further details about its rich phase diagram. |
Wednesday, March 8, 2023 1:54PM - 2:06PM |
N56.00011: Electronic and magnetic phase diagrams of Kitaev quantum spin liquid candidate Na2Co2TeO6 Shengzhi Zhang, Minseong Lee, Sangyun Lee, Andrew J Woods, Sean Thomas, Roman Movshovich, Eric Brosha, Qing Huang, Haidong Zhou, Vivien Zapf We present a comprehensive temperature-magnetic field phase diagrams of the Kitaev spin liquid candidate Na2Co2TeO6 (NCTO) up to 14 T along both a- and a*-axes constructed from the DC/AC magnetization, specific heat, dielectric constant, magnetostriction, and magnetocaloric effect measurements. Three successive field-induced phases are observed below the antiferromagnetic phase transition. Magnetization data up to 60 T revealed no additional transitions at higher fields. Hence, we argue that the magnetic phase diagram of Na2Co2TeO6 is qualitatively different from that of RuCl3. The matching phase boundaries between magnetic and dielectric measurements and peaks in the dielectric constant strongly suggest a magnetoelectric coupling existing in the system. One major debate on NCTO is whether the spin structure of the low-field ground state is zig-zag or triple-Q. We found that the critical fields observed along the a- and a*-axes are significantly different. This is more consistent with the zigzag scenario as it naturally has drastically different spin configurations along the two directions whereas the difference is rather small in triple-Q scenario. In addition, the lack of any change in net electric polarization with temperature or field across the magnetic phase transitions is consistent with a no mirror-breaking symmetry, and thus with the zigzag spin structure. Electric polarization was measured for single-crystals along a*-axis with H || a-axis and in a large polycrystal. |
Wednesday, March 8, 2023 2:06PM - 2:18PM |
N56.00012: On the in-plane anisotropy of planar thermal Hall effect and thermal conductivity osccilation in RuCl3 Heda Zhang, Andrew F May, Jiaqiang Yan, Michael A McGuire, Brian C Sales Growing experiment evidence support the existence of Kitaev spin liquid phase in RuCl3 with an in-plane magnetic field. Thermal transport measurements have shown oscillation of thermal conductivity (kxx) and planar thermal Hall conductivity (kxy) in RuCl3, both were claimed to be associated with the underlying Kitaev spin liquid phase. However, these remarkable results are marred by extrinsic factors (stacking fault, etc). Here, we aim to provide further insights to the Kitaev physics of RuCl3 by studying the anisotropy behavior of thermal conductivity (ka, kb) and thermal Hall conductivity (kab, kba), in the presence of parallel and orthogonal applied magnetic field (Ba, Bb), on the same sample. I will present our initial results, with four different configurations on two samples (from the same batch). The oscillation of ka and kb were observed in all configurations, showing different peaks and valley with fields applied parallel/perpendicular to the Ru-Ru bond. The thermal Hall signal kab(j//a) and kba (j//b) is only present when field is applied along a-axis. Their behavior is slightly anisotropic, reaching half-quantization value only in the intermediate temperature range. Theoretical interpretation of our results are still on-going. |
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