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Topological electronic crystals in twisted bilayer-trilayer graphene

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arXiv 2024年

作者： Su, Ruiheng Waters, Dacen Zhou, Boran Watanabe, Kenji Taniguchi, Takashi Zhang, Ya-Hui Yankowitz, Matthew Folk, Joshua Quantum Matter Institute University of British Columbia VancouverBCV6T 1Z1 Canada Department of Physics and Astronomy University of British Columbia VancouverBCV6T 1Z1 Canada Department of Physics University of Washington SeattleWA98195 United States Intelligence Community Postdoctoral Research Fellowship Program University of Washington SeattleWA98195 United States Department of Physics and Astronomy Johns Hopkins University BaltimoreMD21205 United States Research Center for Electronic and Optical Materials National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan Research Center for Materials Nanoarchitectonics National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan Department of Materials Science and Engineering University of Washington SeattleWA98195 United States

In a dilute two-dimensional electron gas, Coulomb interactions can stabilize the formation of a Wigner crystal [1-3]. Although Wigner crystals are topologically trivial, it has been predicted that electrons in a partially-filled band can break continuous translational symmetry and time-reversal symmetry spontaneously to form a form of topological electron crystal known as an anomalous Hall crystal [4-11]. Here, we report the observation of a generalized version of the anomalous Hall crystal in twisted bilayer-trilayer graphene, whose formation is driven by the moiré potential. The crystal forms at a band filling factor of one electron per four moiré unit cells (ν = 1/4) and quadruples the unit-cell area, coinciding with an integer quantum anomalous Hall effect. The Chern number of the state is exceptionally tunable, and can be switched reversibly between +1 and -1 by electric and magnetic fields. Several other topological electronic crystals arise in a modest magnetic field, originating from ν = 1/3, 1/2, 2/3, and 3/2. The quantum geometry of the folded bands is likely very different from that of the original parent band, enabling possible future discoveries of correlationdriven topological phenomena. © 2024, CC BY.

关键词： Crystal symmetry

Interplay of electronic crystals with integer and fractional Chern insulators in moiré pentalayer graphene

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arXiv 2024年

作者： Waters, Dacen Okounkova, Anna Su, Ruiheng Zhou, Boran Yao, Jiang Watanabe, Kenji Taniguchi, Takashi Xu, Xiaodong Zhang, Ya-Hui Folk, Joshua Yankowitz, Matthew Department of Physics University of Washington SeattleWA98195 United States Intelligence Community Postdoctoral Research Fellowship Program University of Washington SeattleWA98195 United States Quantum Matter Institute University of British Columbia VancouverBCV6T 1Z1 Canada Department of Physics and Astronomy University of British Columbia VancouverBCV6T 1Z1 Canada Department of Physics and Astronomy Johns Hopkins University BaltimoreMD21205 United States Research Center for Electronic and Optical Materials National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan Research Center for Materials Nanoarchitectonics National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan Department of Materials Science and Engineering University of Washington SeattleWA98195 United States

The rapid development of moiré quantum matter has recently led to the remarkable discovery of the fractional quantum anomalous Hall effect [1–6], and sparked predictions of other novel correlation-driven topological states [7–29]. Here, we investigate the interplay of electronic crystals with integer and fractional Chern insulators in a moiré lattice of rhomobohedral pentalayer graphene (RPG) aligned with hexagonal boron nitride. At a doping of one electron per moiré unit cell, we see a correlated insulator with a Chern number that can be tuned between C = 0 and +1 by an electric displacement field, accompanied by an array of other such insulators formed at fractional band fillings, ν. Collectively, these states likely correspond to trivial and topological electronic crystals, some of which spontaneously break the discrete translational symmetry of the moiré lattice. Upon applying a modest magnetic field, a narrow region forms around ν = 2/3 in which transport measurements imply the emergence of a fractional Chern insulator, along with hints of weaker states at other fractional ν. In the same sample, we also see a unique sequence of incipient Chern insulators arising over a broad range of incommensurate band filling near two holes per moiré unit cell. Our results establish moiré RPG as a fertile platform for studying the competition and potential intertwining of electronic crystallization and topological charge fractionalization. Copyright © 2024, The Authors. All rights reserved.

关键词： Quantum Hall effect

Optical and Mechanical Properties of Rutile TiO2 Subjected to AC Flash Processing

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SSRN

SSRN 2024年

作者： Masuda, Hiroshi Tokunaga, Tomoharu Yamamoto, Takahisa Yoshida, Hidehiro Department of Materials Science and Engineering School of Engineering The University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo113-8656 Japan Department of Materials Design Innovation Engineering School of Engineering Nagoya University Furo-cho Chikusa-ku Nagoya464-8603 Japan Next Generation Zirconia Social Cooperation Program Institute of Engineering Innovation The University of Tokyo 2-11-16 Yayoi Bunkyo-ku Tokyo113-8656 Japan

Unusual physical properties associated with lattice defects induced by flash sintering and processing of oxide ceramics have attracted attentions. In this study, optical and mechanical properties of undoped and polycrystalline rutile TiO2 subjected to alternating current (AC) flash processing were characterized through diffuse reflectance spectroscopy and nanoindentation experiments at room temperature. The flashed sample exhibited substantial optical blackening and elastic softening but negligible changes in the hardness and crystal structure. The elastic softening demonstrated a significant rate dependence (i.e., elastic moduli decreased with testing rate) indicating anelasticity, which was possibly caused by stress-induced reordering of point defect dipoles induced by AC flash processing. This anelasticity suggests that pronounced ionic mobility is obtained by flash processing even in undoped systems, which can potentially be extended to a general understanding of mass transport phenomena in transient metal oxides in strong electric fields. © 2024, The Authors. All rights reserved.

关键词： Nanoindentation

Fate of multipolar physics in 5d2 double perovskites

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arXiv 2023年

作者： Rayyan, Ahmed Liu, Xiaoyu Kee, Hae-Young Department of Physics University of Toronto TorontoONM5S 1A7 Canada Department of Materials Science and Engineering University of Washington SeattleWA98195 United States CIFAR Program in Quantum Materials Canadian Institute for Advanced Research TorontoONM5G 1M1 Canada

In a cubic environment, the ground state of spin-orbit coupled 5d2 ions is a non-Kramers Eg doublet, which hosts quadrupole and octupole moments. A series of 5d2 osmium double perovskites Ba2MOsO6 (M = Mg, Ca, Zn, Cd) have recently been proposed to exhibit multipolar orders. We investigate the structural properties of these materials using ab-initio calculations and find that the cubic structure is unstable for the Cd compound while the Mg, Ca, and Zn materials retain Fm3¯m symmetry. We show that Ba2CdOsO6 favours a rhombohedral R3¯ structure characterized by a−a−a− octahedral tiltings as indicated by unstable T1g phonon modes. Trigonal distortions split the excited T2g triplet into an Eg′ doublet and an Ag singlet, which may cross energy levels with the Eg doublet and suppress the multipolar physics. We find a window where Eg remains the lowest energy state under trigonal distortion, enabling the emergence of multipole phases in non-cubic crystal environments. © 2023, CC BY.

关键词： Barium compounds

Thermodynamic modeling of the LiCl-KCl-LaCl3 system with Bayesian model selection and uncertainty quantification

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arXiv 2024年

作者： Gong, Rushi Shang, Shun-Li Goncharov, Vitaliy G. Cockrell, Cillian Trachenko, Kostya Bingham, Paul A. Guo, Xiaofeng Liu, Zi-Kui Department of Materials Science and Engineering The Pennsylvania State University University ParkPA16802 United States Department of Chemistry Washington State University PullmanWA99164 United States Materials Science and Engineering Program Washington State University PullmanWA99164 United States Nuclear Futures Institute Bangor University BangorLL57 1UT United Kingdom School of Physical and Chemical Sciences Queen Mary University of London Mile End Road LondonE1 4NS United Kingdom Materials and Engineering Research Institute Sheffield Hallam University SheffieldS1 1WB United Kingdom

Chloride molten salts are increasingly used in pyroprocessing techniques for the separation of lanthanides. Understanding thermodynamic properties of these salts is essential to predict their critical characteristics and optimize the separation process. Several thermodynamic models, including the associate model, the two-sublattice ionic model, and the modified quasichemical model with quadruplet approximation (MQMQA), have been utilized in the literature to capture the complexity of molten salts. In the present work, the Bayes factor is used to guide the model selection process for thermodynamic modeling of the KCl-LaCl3 system and provide statistical comparison of various models. The results indicate that the MQMQA model is the most favorable one based on available data. The LiCl-KCl-LaCl3 system has been further modelled with uncertainty quantification (UQ) using MQMQA with the thermodynamic properties of compounds in KCl-LaCl3 predicted by the quasiharmonic approach in terms of first-principles phonon calculations as a function of temperature. The calculated phase stability shows excellent agreement with experimental data, indicating that an appropriate thermodynamic model is important for accurately predicting critical characteristics of complex molten salts. © 2024, CC BY-NC-SA.

关键词： Lithium Chloride

No external load measurement strategy for micro thermoelectric generator based on high-performance Si_(1-x-y)Ge_(x)Sn_(y) film

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Journal of Materiomics 2021年第4期7卷 665-671页

作者： Ying Peng Sijing Zhu Huajun Lai Jie Gao Masashi Kurosawa Osamu Nakatsuka Sakae Tanemura Biaolin Peng Lei Miao Guangxi Key Laboratory of Information Material School of Material Science and EngineeringGuilin University of Electronic TechnologyGuilin541004China Department of Materials Physics Graduate School of EngineeringNagoya UniversityNagoya464-8603Japan PRESTO Japan Science and Technology Agency4-1-8HonchoKawaguchiSaitama332-0012Japan Institute of Materials and Systems for Sustainability Nagoya UniversityNagoya464-8601Japan Japan Fine Ceramics Center 2-4-1 MutsunoAtsuta-kuNagoya456-8587Japan Center on Nanoenergy Research Guangxi Key Laboratory of Processing for Non-ferrous Metal and Featured MaterialsGuangxi Key Laboratory for Relativity AstrophysicsNanning530004China Department of Materials Science and Engineering SIT Research LaboratoriesInnovative Global ProgramFaculty of EngineeringShibaura Institute of TechnologyTokyo135-8548Japan

In this study,a micro in-plane p-type thermoelectric generator(TEG),which consists of thin-film Si_(1-x-y)Ge_(x)Sn_(y) ternary alloy semiconductor on insulator,is developed to make efficient use of waste heat such as human body.A power factor value as high as 1095 mWm^(-1) K^(-2) had been achieved using Bion implanted and short-term rapid thermal annealing(RTA)*** addition,a measuring scheme for micro TEG without external load resistance was *** one measuring session,multiple parameters can be *** micro single-arm TEG prepared by semiconductor process can output 0.29 nW power at a temperature difference of 15 K,and a cross-sectional power density has reached up to 0.58 mW/cm^(2),which is a superior value for wearable *** findings of this study have important reference value for wearable device performance improvement and output power measuring of micro TEG.

关键词： Si_(1-x-y)Ge_(x)Sn_(y) film P-type TEG No external load measurement Ambient power density

Mitigating oxygen reduction reaction barriers: An in-depth first-principles exploration of high-entropy alloy as catalysts

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Electrochemistry Communications 2024年 166卷

作者： Chen, Ming-Yi Thanh Thuy Tran, Ngoc Hsu, Wen-Dung Department of Materials Science and Engineering National Cheng Kung University 1 University Road Tainan701 Taiwan Research Center National Cheng Kung University Tainan701 Taiwan Program on Semiconductor Packaging and Testing Academy of Innovative Semiconductor and Sustainable Manufacture National Cheng Kung University Tainan701 Taiwan

This study investigates the effectiveness of high-entropy alloys (HEAs) as catalysts for reducing the energy barrier of the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). Four HEAs—IrPdPtRh, CoCrFeNi, NbMoTaW, and TiZrNbTa—are analyzed as potential catalysts. This superiority arises from the shift in the overall d-band center position towards negative energy in HEAs. The study suggests that an increased standard deviation of atomic valences within HEAs correlates positively with improved ORR efficiency, indicating it as a potential design indicator for cost-effective catalysts. Moreover, predictions of valence variations based on differences in electronegativity between individual elements are proposed. Additionally, the research highlights that additional surface adsorption of Pt on HEAs would further enhance ORR activity. © 2024

关键词： Catalysts

Enhancing oxygen reduction reaction with Pt-decorated Cu@Pd and high-entropy alloy catalysts: Insights from first-principles analysis of Pt arrangement

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Applied Catalysis A: General 2024年 669卷

作者： Chen, Ming-Yi Tran, Ngoc Thanh Thuy Alao, Ahmed Abubakar Hsu, Wen-Dung Department of Materials Science and Engineering National Cheng Kung University 1 University Road Tainan701 Taiwan Research Center National Cheng Kung University Tainan701 Taiwan Program on Semiconductor Packaging and Testing Academy of Innovative semiconductor and Sustainable Manufacture National Cheng Kung University Tainan701 Taiwan

The efficiency of oxygen reduction reaction (ORR) in the proton-exchange membrane fuel cells (PEMFCs) heavily relies on the surface Pt atom arrangement, which can be represented by the Pt-Pt average distance. Here, we employed density functional theory (DFT) to examine the influence of Pt arrangement on the ORR efficiency of Cu@Pd core-shell and high-entropy alloy catalysts. Our DFT calculations reveal that a shorter Pt-Pt average distance on the surface leads to a lower O2 dissociation barrier. Nevertheless, a shorter Pt-Pt average distance is not thermodynamically favored for the Cu@Pt catalyst. Moreover, we discovered a robust correlation between the level of the d-band center of the catalyst and the O2 adsorption energy. To explore the potential of controlling Pt arrangement, we investigated the use of NbMoTaW high-entropy alloy (HEA) substrates. Our findings suggest that HEA substrates provide promising surface chemistry for tuning Pt arrangement and controlling the O2 dissociation barrier. © 2023

关键词： Oxygen

Acid-catalyzed hydrothermal treatment of sewage sludge: effects of reaction temperature and acid concentration on the production of hydrolysis by-products

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Biomass Conversion and Biorefinery 2023年第9期13卷 7533-7546页

作者： Pham, Van Toi Guan, Chung-Yu Han, Po-Chun Matsagar, Babasaheb M. Wu, Kevin C. W. Ahamad, Tansir Chang, Ching-Yuan Yu, Chang-Ping Graduate Institute of Environmental Engineering National Taiwan University Taipei106 Taiwan Faculty of Environmental Engineering National University of Civil Engineering 55 Giai Phong Hai Ba Trung Hanoi100000 Viet Nam Department of Environmental Engineering National Ilan University Yilan260 Taiwan Ph.D. Program of Green Materials and Precision Devices National Taiwan University Taipei10617 Taiwan Department of Chemical Engineering National Taiwan University No. 1 Sec. 4 Roosevelt Road Taipei10617 Taiwan Department of Chemistry College of Science King Saud University P.O. Box 2455 Riyadh11451 Saudi Arabia Water Innovation Low Carbon and Environmental Sustainability Research Center National Taiwan University Taipei106 Taiwan

Sewage sludge (SS) is an organic biomass from wastewater treatment plants, but the use of SS to produce bio-based chemicals under acid-catalyzed hydrolysis (ACH) processes is not well investigated. In this study, ACH processes were performed at 120, 150, and 180 °C using sulfuric acid (H2SO4) with concentrations of 0–0.5 M within a reaction time of 90–180 min to produce bio-based chemicals from SS. The results showed that the reaction temperature, reaction time, and concentrations of H2SO4 affected the yields of sugars, levulinic acid (LA), and 5-hydroxymethylfurfural (HMF). The highest xylose and glucose yields were 7.69 mol% and 5.22 mol% at 120 °C with 0.5 M H2SO4 during the 180 min of reaction time, respectively. Besides, under the ACH process at 180 °C and 180 min, the yield of LA reached a maximum value of 0.48 mol% at 0.5 M H2SO4, and the highest yield of HMF was 1.66 mol% at 0.1 M H2SO4. The data obtained also indicated that the ACH process led to an increase in soluble chemical oxygen demand, dissolved organic carbon, and total dissolved nitrogen. Fluorescence excitation-emission matrix of dissolved organic matter and thermogravimetric analysis of the treated SS further supported the enhanced solubilization of SS after ACH process, especially under higher reaction temperature and concentrations of H2SO4. Although the lower yields of bio-based chemicals might restrict the downstream recovery of the target products, the largely improved SS solubilization by ACH suggests that acid-catalyzed hydrothermal hydrolysis process has potential as an alternative pretreatment method of SS. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.

关键词： Sewage sludge