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Influence of Ru-substitution on the performance of pyrochlore catalysts in oxidative steam reforming of ethanol

Sustainable Energy and Fuels 2024年第9期8卷 2104-2114页

作者： Huang, Yu-Hsuan Hsieh, Ho-Chen Wang, Yun-Hsin Weng, Sheng-Feng Lee, Chi-Shen Department of Applied Chemistry National Yang Ming Chiao Tung University 1001 University Rd Hsinchu 30010 Taiwan Graduate Degree Program of Science and Technology of Accelerator Light Source National Yang Ming Chiao Tung University Hsinchu 30010 Taiwan Center for Emergent Functional Matter Science National Chiao-Tung University Hsinchu 30010 Taiwan

This study introduces a series of Ru-substituted pyrochlore catalysts, achieved by using La2Zr2−xRuxO7−δ (LZRO-00-04, x = 0.0-0.4) during the oxidative steam reforming of ethanol reaction (OSRE). The samples were cha...

This study introduces a series of Ru-substituted pyrochlore catalysts, achieved by using La₂Zr_2−xRu_xO_7−δ (LZRO-00-04, x = 0.0-0.4) during the oxidative steam reforming of ethanol reaction (OSRE). The samples were characterized using X-ray diffraction (XRD), temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS). The reduction behavior and catalytic performance correlate directly with the Ru content. The 5 wt% LZRO02 catalytic system outperforms the supported Ru-based catalyst (5 wt% RuO₂/LZO), boasting lower Ru concentrations (2.66 wt%). The enhancement is attributed to the uniform dispersion of Ru ≥ 4+ ions embedded within the pyrochlore structure, as convincingly supported by the XPS result. This underscores notable distinctions between the internal and external structures of the two systems. On the other hand, our extensive long-term testing of LZRO02 across γ-Al₂O₃ and lab-made LZO carriers, coupled with meticulous mapping and Raman analysis, revealed a significant observation: the catalyst exhibits notably reduced aggregation tendencies and enhanced activity when utilized on the LZO carrier. The La₂Zr_1.8Ru_0.2O_7−δ catalyst supported on LZO demonstrated selectivity of hydrogen S_H = 86.4(1)%;Y_H = 2.55(3) (mol/mol EtOH) for long-term stability tests at T = 400 °C, C/O = 0.6, and O₂/C₂H₅OH = 1.5. This discovery underscores the catalyst's remarkable stability and activity, making it a promising candidate for catalytic applications. © 2024 The Royal Society of Chemistry.

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Reuse of sodium–doped iridium oxide nanoparticles as a bio–stimulating electrode by a chemical and electrochemical recovery process

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Ceramics International 2024年第4期50卷 6220-6228页

作者： Tso, Kuang-Chih Chen, Chieh-Hsuan Chen, Po-Chun Li, Shao-Sian Chen, Jeng-Lung Ohta, Jun Wu, Pu-Wei Division of Materials Science Graduate School of Science and Technology Nara Institute of Science and Technology Nara630-0192 Japan Graduate Degree Program of Science and Technology of Accelerator Light Source National Yang Ming Chiao Tung University Hsinchu300 Taiwan Department of Materials Science and Engineering National Yang Ming Chiao Tung University Hsinchu300 Taiwan Institute of Materials Science and Engineering National Taipei University of Technology Taipei106 Taiwan National Synchrotron Radiation Research Center Hsinchu300 Taiwan

A sequential chlorination and electrochemical reduction process is demonstrated to convert Na–doped iridium oxide nanoparticles into useful IrIIICl63−(aq) serving as the precursor for the fabrication of bio–stimulating electrode. The Na–doped iridium oxide nanoparticles are treated in 35 wt% hydrochloric acid at 70 °C for 18 h to form IrIVCl62−(aq) with pH of 0.3, so the latter could be readily reduced to IrIIICl63−(aq) at a potentiostatic mode of 0.6 V (vs. SCE). The oxidation state and the nature of complexing ligands for the regenerated IrIIICl63− and IrIVCl62−, as well as commercially available IrIIICl63− are validated by X–ray Absorption Spectroscopy. UV–Vis profiles of regenerated IrIVCl62−(aq) are recorded and the absorbance at 487 nm signal is benchmarked against that of standard IrIVCl62−(aq) to obtain the effective regeneration ratio of 68.6%. X–ray diffraction patterns of Na–doped iridium oxide nanoparticles before and after the annealing treatment indicate the amorphous structure facilitates the chlorination step. The regenerated IrIIICl63− is reused to synthesize Na–doped iridium oxide thin film serving as a bio–stimulating electrode for implantable bio–electronics. The regenerated Na–doped iridium oxide thin film reveals a charge-storage capacity of 0.32 mC/cm2-nm and impressive stability that are comparable to those of fresh Na–doped iridium oxide thin film derived from commercially available IrIIICl63−. © 2023 Elsevier Ltd and Techna Group S.r.l.

关键词： Transition metal oxides

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A robust bendable IrO_x thin film via mild alkaline solution process for neuron stimulating electrodes

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Surfaces and Interfaces 2024年 44卷

作者： Tso, Kuang-Chih Chan, Tzu-Ying Yu, Tsung-Chun Tao, Yu-Jen Chu, Chao-Yi Chen, San-Yuan Lee, Jyh-Fu Ohta, Jun Chen, Po-Chun Wu, Pu-Wei Graduate Program of Accelerator Light Source National Yang Ming Chiao Tung University Hsinchu 300 Taiwan Division of Materials Science Graduate School of Science and Technology Nara Institute of Science Technology Nara Ikoma Takayama 8916-5 Japan Department of Materials Science and Engineering National Yang Ming Chiao Tung University Hsinchu 300 Taiwan Institute of Materials Science and Engineering National Taipei University of Technology Taipei 106 Taiwan National Synchrotron Radiation Research Center Hsinchu 300 Taiwan

We demonstrate a unique chemical formula to deposit hydrous iridium oxide thin film on a platinum-coated polyimide substrate. In a mild alkaline solution, the iridium (III) precursor undergoes the ligand exchange and hydrolysis reaction to become the iridium (III) dimers that are physically adsorbed on the substrate for subsequent heterogeneous condensation and growth of amorphous hydrous iridium oxide thin film. Both UV–Vis and X-ray absorption spectroscopy (XAS) are employed to determine the reaction steps involved. The chemical nature and crystallinity of the hydrous iridium oxide thin film are investigated by XAS, X-ray photon spectroscopy, and X-ray diffraction. The hydrous iridium oxide thin film reveals an impressive normalized charge storage capacity (CSC) of 0.3 mC/cm²-nm and a low impedance (80.5 Ω) at 1k Hz. In addition, in bending test of 3,000 cycles, the hydrous iridium oxide thin film retains 91.2 % of its initial normalized CSC without any physical crack and delamination. The cell viability test suggests negligible bio-toxicity. Our results provide a solid evidence of fabricating a robust flexible electrode for neural interfaces for potential use in implantable electronic devices. © 2023 Elsevier B.V.

关键词： Bio-electrode Flexible substrate Implantable electronic devices Iridium dimers Iridium oxide Polyimide

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A Robust Bendable Irox Thin Film Via Mild Alkaline Solution Process for Neuron Stimulating Electrodes

SSRN

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SSRN 2023年

作者： Tso, Kuang-Chih Chan, Tzu-Ying Yu, Tsung-Chun Pan, Shih-Chin Chu, Chao-Yi Chen, San-Yuan Lee, Jyh-Fu Ohta, Jun Wu, Pu-Wei Chen, Po-Chun Graduate Program of Accelerator Light Source National Yang Ming Chiao Tung University Hsinchu300 Taiwan Division of Materials Science Graduate School of Science and Technology Nara Institute of Science Technology Takayama Ikoma Nara8916-5 Japan Department of Materials Science and Engineering National Yang Ming Chiao Tung University Hsinchu300 Taiwan Institute of Materials Science and Engineering National Taipei University of Technology Taipei106 Taiwan National Synchrotron Radiation Research Center Hsinchu300 Taiwan

We demonstrate a unique chemical formula to deposit hydrous iridium oxide thin film on a platinum-coated polyimide substrate. In a mild alkaline solution, the iridium (III) precursor undergoes the ligand exchange and hydrolysis reaction to become the iridium (III) dimers that are physically adsorbed on the substrate for subsequent heterogeneous condensation and growth of amorphous hydrous iridium oxide thin film. Both UV-Vis and X-ray absorption spectroscopy (XAS) are employed to determine the reaction steps involved. The chemical nature and crystallinity of the hydrous iridium oxide thin film are investigated by XAS, X-ray photon spectroscopy, and X-ray diffraction. The hydrous iridium oxide thin film reveals an impressive normalized charge storage capacity (CSC) of 0.3 mC/cm2-nm and a low impedance (80.5 Ω) at 1k Hz. In addition, in bending test of 3,000 cycles, the hydrous iridium oxide thin film retains 91.2% of its initial normalized CSC without any physical crack and delamination. The cell viability test suggests negligible bio-toxicity. Our results provide a solid evidence of fabricating a robust flexible electrode for neural interfaces for potential use in implantable electronic devices. © 2023, The Authors. All rights reserved.

关键词： Iridium compounds

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Ubiquitous Flat Bands in a Cr-based Kagome Superconductor

arXiv

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arXiv 2024年

作者： Guo, Yucheng Wang, Zehao Xie, Fang Huang, Yuefei Gao, Bin Oh, Ji Seop Wu, Han Liu, Zhaoyu Ren, Zheng Fang, Yuan Biswas, Ananya Zhang, Yichen Yue, Ziqin Hu, Cheng Jozwiak, Chris Bostwick, Aaron Rotenberg, Eli Hashimoto, Makoto Lu, Donghui Kono, Junichiro Chu, Jiun-Haw Yakobson, Boris I. Birgeneau, Robert J. Si, Qimiao Dai, Pengcheng Yi, Ming Department of Physics and Astronomy Rice University HoustonTX77005 United States Advanced Light Source Lawrence Berkeley National Laboratory BerkeleyCA94720 United States Department of Materials Science and NanoEngineering Rice University HoustonTX77005 United States Department of Physics University of California BerkeleyCA94720 United States Department of Physics University of Washington Washington98105 United States Applied Physics Graduate Program Smalley-Curl Institute Rice University HoustonTX77005 United States Stanford Synchrotron Radiation Lightsource SLAC National Accelerator Laboratory Menlo ParkCA94025 United States Department of Electrical and Computer Engineering Rice University HoustonTX77005 United States Smalley-Curl Institute Rice University HoustonTX77005 United States Department of Materials Science and NanoEngineering Rice University HoustonTX77005 United States

In the quest for novel quantum states driven by topology and correlation, kagome lattice materials have garnered significant interest due to their distinctive electronic band structures, featuring flat bands (FBs) arising from the quantum destructive interference of the electronic wave function. The tuning of the FBs to the chemical potential would lead to the possibility of liberating electronic instabilities that lead to emergent electronic orders. Despite extensive studies, direct evidence of FBs tuned to the chemical potential and their participation in emergent electronic orders have been lacking in bulk quantum materials. Here using a combination of Angle-Resolved Photoemission Spectroscopy (ARPES) and Density Functional Theory (DFT), we reveal that the low-energy electronic structure of the recently discovered Cr-based kagome metal superconductor CsCr3Sb5 is dominated by a pervasive FB in close proximity to, and below the Fermi level. A comparative analysis with orbital-projected DFT and polarization dependence measurement uncovers that an orbital-selective renormalization mechanism is needed to reconcile the discrepancy with the DFT calculations, which predict the FB to appear 200 meV above the Fermi level. Furthermore, we observe the FB to shift away from the Fermi level by 20 meV in the low-temperature density wave-ordered phase, highlighting the role of the FB in the emergent electronic order. Our results reveal CsCr3Sb5 to stand out as a promising platform for further exploration into the effects of FBs near the Fermi level on kagome lattices, and their role in emergent orders in bulk quantum materials. © 2024, CC BY.

关键词： Density functional theory

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Spectral evidence for unidirectional charge density wave in detwinned BaNi2As2

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Physical Review B 2023年第8期108卷 L081104-L081104页

作者： Yucheng Guo Mason Klemm Ji Seop Oh Yaofeng Xie Bing-Hua Lei Luca Moreschini Cheng Chen Ziqin Yue Sergey Gorovikov Tor Pedersen Matteo Michiardi Sergey Zhdanovich Andrea Damascelli Jonathan Denlinger Makoto Hashimoto Donghui Lu Chris Jozwiak Aaron Bostwick Eli Rotenberg Sung-Kwan Mo Rob G. Moore Junichiro Kono Robert J. Birgeneau David J. Singh Pengcheng Dai Ming Yi Department of Physics and Astronomy Rice University Houston Texas 77005 USA Advanced Light Source Lawrence Berkeley National Laboratory Berkeley California 94720 USA Department of Physics University of California Berkeley California 94720 USA Department of Physics and Astronomy University of Missouri Columbia Missouri 65211 USA Materials Science Division Lawrence Berkeley National Laboratory Berkeley California 94720 USA Department of Physics University of Oxford Oxford OX1 3PU United Kingdom Applied Physics Graduate Program Smalley-Curl Institute Rice University Houston Texas 77005 USA Canadian Light Source Inc. 44 Innovation Boulevard Saskatoon SK S7N 2V3 Canada Department of Physics and Astronomy University of British Columbia Vancouver British Columbia V6T 1Z1 Canada Quantum Matter Institute University of British Columbia Vancouver British Columbia V6T 1Z4 Canada Max Planck Institute for Chemical Physics of Solids Nöthnitzer Straße 40 01187 Dresden Germany Stanford Synchrotron Radiation Lightsource SLAC National Accelerator Laboratory Menlo Park California 94025 USA Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Department of Electrical and Computer Engineering Rice University Houston Texas 77005 USA Smalley-Curl Institute Rice University Houston Texas 77005 USA Department of Materials Science and NanoEngineering Rice University Houston Texas 77005 USA Department of Chemistry University of Missouri Columbia Missouri 65211 USA

In the iron-based superconductors, unconventional superconductivity emerges in proximity to intertwined electronic orders consisting of an electronic nematic order and a spin density wave (SDW). Recently, BaNi2As2, like its well-known iron-based analog BaFe2As2, has been discovered to host a symmetry-breaking structural transition but coupled to a unidirectional charge density wave (CDW) instead of SDW, providing a novel platform to study intertwined orders. Here, through a systematic angle-resolved photoemission spectroscopy study combined with a detwinning B1g uniaxial strain, we identify distinct spectral evidence of band evolution due to the structural transition as well as CDW-induced band folding. In contrast to the nematicity and spin density wave in BaFe2As2, the structural and CDW order parameters in BaNi2As2 are observed to be strongly coupled and do not separate in the presence of uniaxial strain. Furthermore, no nematic band splitting is resolved above the structural transition. Our measurements point to a likely lattice origin of the CDW order in BaNi2As2.

关键词： Charge density waves Nematic phase transition Iron-based superconductors Angle-resolved photoemission spectroscopy

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Kramers Nodal Lines and Weyl Fermions in SmAlSi

arXiv

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arXiv 2022年

作者： Zhang, Yichen Gao, Yuxiang Gao, Xue-Jian Lei, Shiming Ni, Zhuoliang Oh, Ji Seop Huang, Jianwei Yue, Ziqin Zonno, Marta Gorovikov, Sergey Hashimoto, Makoto Lu, Donghui Denlinger, Jonathan D. Birgeneau, Robert J. Kono, Junichiro Wu, Liang Law, Kam Tuen Morosan, Emilia Yi, Ming Department of Physics and Astronomy Rice University HoustonTX77005 United States Department of Physics Hong Kong University of Science and Technology Clear Water Bay Hong Kong Department of Physics and Astronomy University of Pennsylvania PhiladelphiaPA19104 United States Department of Physics University of California BerkeleyCA94720 United States Applied Physics Graduate Program Smalley-Curl Institute Rice University HoustonTX77005 United States Canadian Light Source Inc. 44 Innovation Boulevard SaskatoonSKS7N 2V3 Canada Stanford Synchrotron Radiation Lightsource SLAC National Accelerator Laboratory 2575 Sand Hill Road Menlo ParkCA94025 United States Advanced Light Source Lawrence Berekeley National Laboratory BerkeleyCA94720 United States Materials Science Division Lawrence Berekeley National Laboratory BerkeleyCA94720 United States Department of Electrical and Computer Engineering Rice University HoustonTX77005 United States Department of Materials Science and Nanoengineering Rice University HoustonTX77005 United States

Kramers nodal lines (KNLs) have recently been proposed theoretically as a special type of Weyl line degeneracy connecting time-reversal invariant momenta. KNLs are robust to spin orbit coupling and are inherent to all non-centrosymmetric achiral crystal structures, leading to unusual spin, magneto-electric, and optical properties. However, their existence in in real quantum materials has not been experimentally established. Here we gather the experimental evidence pointing at the presence of KNLs in SmAlSi, a non-centrosymmetric metal that develops incommensurate spin density wave order at low temperature. Using angle-resolved photoemission spectroscopy, density functional theory calculations, and magneto-transport methods, we provide evidence suggesting the presence of KNLs, together with observing Weyl fermions under the broken inversion symmetry in the paramagnetic phase of SmAlSi. We discuss the nesting possibilities regarding the emergent magnetic orders in SmAlSi. Our results provide a solid basis of experimental observations for exploring correlated topology in SmAlSi. © 2022, CC BY-NC-SA.

关键词： Temperature

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Two-step electronic response to magnetic ordering in a van der Waals ferromagnet

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Physical Review B 2024年第4期109卷 045416-045416页

作者： Han Wu Jian-Xin Zhu Lebing Chen Matthew W. Butcher Ziqin Yue Dongsheng Yuan Yu He Ji Seop Oh Bin Gao Jianwei Huang Shan Wu Cheng Gong Yucheng Guo Sung-Kwan Mo Jonathan Denlinger Donghui Lu Makoto Hashimoto Matthew B. Stone Alexander I. Kolesnikov Songxue Chi Junichiro Kono Andriy H. Nevidomskyy Robert J. Birgeneau Pengcheng Dai Ming Yi Department of Physics and Astronomy and Rice Center for Quantum Materials Rice University Houston Texas 77005 USA Theoretical Division Los Alamos National Laboratory Los Alamos New Mexico 87545 USA Center for Integrated Nanotechnologies Los Alamos National Laboratory Los Alamos New Mexico 87545 USA Department of Physics University of California at Berkeley Berkeley California 94720 USA Applied Physics Graduate Program Smalley-Curl Institute Rice University Houston Texas 77005 USA Materials Sciences Division Lawrence Berkeley National Laboratory Berkeley California 94720 USA National Institute for Materials Science 1-1 Namiki Tsukuba Ibaraki 305-0044 Japan Department of Applied Physics Yale University New Haven Connecticut 06511 USA Department of Electrical and Computer Engineering and Quantum Technology Center University of Maryland College Park Maryland 20742 USA Advanced Light Source Lawrence Berkeley National Laboratory Berkeley California 94720 USA Stanford Synchrotron Radiation Lightsource SLAC National Accelerator Laboratory Menlo Park California 94025 USA Neutron Scattering Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Department of Electrical and Computer Engineering Rice University Houston Texas 77005 USA Smalley-Curl Institute Rice University Houston Texas 77005 USA Department of Material Science and Nanoengineering Rice University Houston Texas 77005 USA Department of Materials Science and Engineering University of California Berkeley California 94720 USA

The two-dimensional material Cr2Ge2Te6 is a member of the class of insulating van der Waals (vdW) magnets. Here, using high resolution angle-resolved photoemission spectroscopy in a detailed temperature dependence study, we identify a clear response of the electronic structure to a dimensional crossover in the form of two distinct temperature scales marking onsets of modifications in the electronic structure. Specifically, we observe Te p-orbital-dominated bands to undergo changes at the Curie transition temperature TC while the Cr d-orbital-dominated bands begin evolving at a higher temperature scale. Combined with neutron scattering, density functional theory calculations, and Monte Carlo simulations, we find that the electronic system can be consistently understood to respond sequentially to the distinct temperatures at which in-plane and out-of-plane spin correlations exceed a characteristic length scale. Our findings reveal the sensitivity of the orbital-selective electronic structure for probing the dynamical evolution of local moment correlations in vdW insulating magnets.

关键词： Electronic structure Magnetic order Magnetic phase transitions Van der Waals systems Angle-resolved photoemission spectroscopy

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Weyl nodal ring states and Landau quantization with very large magnetoresistance in square-net magnet EuGa4

arXiv

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arXiv 2022年

作者： Lei, Shiming Allen, Kevin Huang, Jianwei Moya, Jaime M. Wu, Tsz Chun Casas, Brian Zhang, Yichen Oh, Ji Seop Hashimoto, Makoto Lu, Donghui Denlinger, Jonathan Jozwiak, Chris Bostwick, Aaron Rotenberg, Eli Balicas, Luis Birgeneau, Robert Foster, Matthew S. Yi, Ming Sun, Yan Morosan, Emilia Department of Physics and Astronomy Rice University HoustonTX77005 United States Applied Physics Graduate Program Rice University HoustonTX77005 United States National High Magnetic Field Laboratory TallahasseeFL32310 United States Department of Physics University of California BerkeleyCA94720 United States Stanford Synchrotron Radiation Lightsource SLAC National Accelerator Laboratory Menlo ParkCA94025 United States Advanced Light Source Lawrence Berkeley National Laboratory BerkeleyCA94720 United States Department of Physics Florida State University TallahasseeFL32306 United States Materials Science Division Lawrence Berkeley National Laboratory BerkeleyCA94720 United States Rice Center for Quantum Materials Rice University HoustonTX77005 United States Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences China

Magnetic topological semimetals (TSMs) allow for an effective control of the topological electronic states by tuning the spin configuration, and therefore are promising materials for next-generation electronic and spintronic applications. Of magnetic TSMs, Weyl nodal-line (NL) semimetals likely have the most tunability, and yet they are the least experimentally studied so far due to the scarcity of material candidates. Here, using a combination of angle-resolved photoemission spectroscopy and quantum oscillation measurements, together with density functional theory calculations, we identify the square-net compound EuGa4 as a new magnetic Weyl nodal ring (NR) semimetal, in which the line nodes form closed rings in the vicinity of the Fermi level. Remarkably, the Weyl NR states show distinct Landau quantization with clear spin splitting upon application of a magnetic field. At 2 K in a field of 14 T, the transverse magnetoresistance of EuGa4 exceeds 200,000%, which is more than two orders of magnitude larger than that of other known magnetic TSMs. High field magnetoresistance measurements indicate no saturation up to 40 T. Our theoretical model indicates that the nonsaturating MR naturally arises as a consequence of the Weyl NR state. Our work thus point to the realization of Weyl NR states in square-net magnetic materials, and opens new avenues for the design of magnetic TSMs with very large magnetoresistance. Copyright © 2022, The Authors. All rights reserved.

关键词： Density functional theory

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Nanoscale visualization and spectral fingerprints of the charge order in ScV6Sn6 distinct from other kagome metals

arXiv

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arXiv 2023年

作者： Cheng, Siyu Ren, Zheng Li, Hong Oh, Ji Seop Tan, Hengxin Pokharel, Ganesh DeStefano, Jonathan M. Rosenberg, Elliott Guo, Yucheng Zhang, Yichen Yue, Ziqin Lee, Yongbin Gorovikov, Sergey Zonno, Marta Hashimoto, Makoto Lu, Donghui Ke, Liqin Mazzola, Federico Kono, Junichiro Birgeneau, R.J. Chu, Jiun-Haw Wilson, Stephen D. Wang, Ziqiang Yan, Binghai Yi, Ming Zeljkovic, Ilija Department of Physics Boston College Chestnut HillMA02467 United States Department of Physics and Astronomy Rice University HoustonTX77005 United States Department of Physics University of California BerkeleyCA94720 United States Department of Condensed Matter Physics Weizmann Institute of Science Rehovot Israel Materials Department University of California Santa Barbara Santa BarbaraCA93106 United States Department of Physics University of Washington SeattleWA98195 United States Ames Laboratory AmesIA50011 United States Canadian Light Source Inc. 44 Innovation Boulevard SaskatoonSKS7N 2V3 Canada Stanford Synchrotron Radiation Lightsource SLAC National Accelerator Laboratory Menlo ParkCA94025 United States CNR Laboratorio TASC Area Science Park S.S.14 km 163.5 TriesteI-34149 Italy Department of Molecular Sciences and Nanosystems Ca' Foscari University of Venice Venice30172 Italy Materials Science Division Lawrence Berkeley National Laboratory BerkeleyCA94720 United States Applied Physics Graduate Program Smalley‐Curl Institute Rice University HoustonTX77005 United States

Charge density waves (CDWs) have been tied to a number of unusual phenomena in kagome metals, including rotation symmetry breaking, time‐reversal symmetry breaking and superconductivity. The majority of the experiments in kagome metals thus far have focused on the CDW states in AV3Sb5 (A=K, Cs, Rb) and FeGe, characterized by the 2a0 by 2a0 CDW period in the kagome plane. Recently, a bulk CDW phase (TCDW ≈ 92 K) with an entirely different wave length and orientation has been reported in ScV6Sn6, as the first realization of a CDW state in the broad RM6X6 crystal structure. Here, using a combination of scanning tunneling microscopy/spectroscopy and angle‐resolved photoemission spectroscopy, we reveal the microscopic structure and the spectroscopic signatures of this charge ordering phase in ScV6Sn6. Differential conductance dI/dV spectra show a partial gap opening in the density‐of‐states of about 20 meV at the Fermi level. This is much smaller than the spectral gaps observed in AV3Sb5 and FeGe despite the comparable TCDW temperatures in these systems, suggesting substantially weaker coupling strength in ScV6Sn6. Surprisingly, despite the three‐dimensional bulk nature of the charge order, we find that the charge modulation is only observed on the kagome termination. Temperature‐dependent band structure evolution suggests a modulation of the surface states as a consequence of the emergent charge order, with an abrupt spectral weight shift below TCDW consistent with the first‐order phase transition. The similarity of the electronic band structures of ScV6Sn6 and TbV6Sn6 (where the charge ordering is absent), together with the first‐principle calculations, suggests that charge ordering in ScV6Sn6 may not be primarily electronically driven. Interestingly, in sharp contrast to the CDW state of cousin AV3Sb5, we find no evidence supporting rotation symmetry breaking. Our results reveal a distinctive nature of the charge ordering phase in ScV6Sn6 in comparison to other kagome

关键词： Charge density waves

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