Pub Date : 2024-11-03DOI: 10.1038/s43246-024-00681-3
Anup Pradhan Sakhya, Brenden R. Ortiz, Barun Ghosh, Milo Sprague, Mazharul Islam Mondal, Matthew Matzelle, Iftakhar Bin Elius, Nathan Valadez, David G. Mandrus, Arun Bansil, Madhab Neupane
Kagome lattices have emerged as an ideal platform for exploring exotic quantum phenomena in materials. Here, we report the discovery of Ti-based kagome metal YbTi3Bi4 which we characterize using angle-resolved photoemission spectroscopy (ARPES) and magneto-transport, in combination with density functional theory calculations. Our ARPES results reveal the complex fermiology of YbTi3Bi4 and provide spectroscopic evidence of four flat bands. Our measurements also show the presence of multiple van Hove singularities originating from Ti 3d orbitals and a linearly-dispersing gapped Dirac-like bulk state at the $$overline{,{mbox{K}},}$$ point in accord with our theoretical calculations. Our study establishes YbTi3Bi4 as a platform for exploring exotic phases in the wider LnTi3Bi4 (Ln = lanthanide) family of materials. Kagome lattices have emerged as an ideal platform for exploring exotic quantum phenomena in materials. Here, the discovery of a Ti-based kagome metal YbTi3Bi4 is reported, showing spectroscopic evidence of four flat bands originating from both Yb 4f and Ti 3d orbitals, multiple van Hove singularities, and a linearly dispersing gapped Dirac-like bulk state.
卡戈米晶格已成为探索材料中奇异量子现象的理想平台。在此，我们报告了钛基卡戈米金属 YbTi3Bi4 的发现，并结合密度泛函理论计算，使用角度分辨光发射光谱（ARPES）和磁传输对其进行了表征。我们的 ARPES 结果揭示了 YbTi3Bi4 的复杂费米学，并提供了四个平坦带的光谱证据。我们的测量结果还显示，在 $$overline,{mbox{K}},}$ 点存在多个源于 Ti 3d 轨道的范霍夫奇点和线性弥散的间隙狄拉克样体态，这与我们的理论计算结果一致。我们的研究将 YbTi3Bi4 树立为探索更广泛的 LnTi3Bi4（Ln = 镧系元素）材料家族中奇异相的平台。卡戈米晶格已成为探索材料中奇异量子现象的理想平台。本文报告了钛基卡戈米金属 YbTi3Bi4 的发现，其光谱显示了源自镱 4f 和钛 3d 轨道的四条平带、多个范霍夫奇点以及线性弥散的间隙狄拉克样体态。
{"title":"Diverse electronic landscape of the kagome metal YbTi3Bi4","authors":"Anup Pradhan Sakhya, Brenden R. Ortiz, Barun Ghosh, Milo Sprague, Mazharul Islam Mondal, Matthew Matzelle, Iftakhar Bin Elius, Nathan Valadez, David G. Mandrus, Arun Bansil, Madhab Neupane","doi":"10.1038/s43246-024-00681-3","DOIUrl":"10.1038/s43246-024-00681-3","url":null,"abstract":"Kagome lattices have emerged as an ideal platform for exploring exotic quantum phenomena in materials. Here, we report the discovery of Ti-based kagome metal YbTi3Bi4 which we characterize using angle-resolved photoemission spectroscopy (ARPES) and magneto-transport, in combination with density functional theory calculations. Our ARPES results reveal the complex fermiology of YbTi3Bi4 and provide spectroscopic evidence of four flat bands. Our measurements also show the presence of multiple van Hove singularities originating from Ti 3d orbitals and a linearly-dispersing gapped Dirac-like bulk state at the $$overline{,{mbox{K}},}$$ point in accord with our theoretical calculations. Our study establishes YbTi3Bi4 as a platform for exploring exotic phases in the wider LnTi3Bi4 (Ln = lanthanide) family of materials. Kagome lattices have emerged as an ideal platform for exploring exotic quantum phenomena in materials. Here, the discovery of a Ti-based kagome metal YbTi3Bi4 is reported, showing spectroscopic evidence of four flat bands originating from both Yb 4f and Ti 3d orbitals, multiple van Hove singularities, and a linearly dispersing gapped Dirac-like bulk state.","PeriodicalId":10589,"journal":{"name":"Communications Materials","volume":" ","pages":"1-7"},"PeriodicalIF":7.5,"publicationDate":"2024-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s43246-024-00681-3.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142574264","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-03DOI: 10.1038/s43246-024-00686-y
Michael K. Koch, Vibhav Bharadwaj, Alexander Kubanek
The coherent control of a two-level system is among the most essential challenges in modern quantum optics. Understanding its fundamental limitations is crucial, also for the realization of next generation quantum devices. The quantum coherence of a two-level system is fragile in particular, when the two levels are connected via an optical transition, which, at the same time, enables the manipulation of the system. When such quantum emitters are located in solids the coherence suffers from the interaction of the optical transition with the solid state environment, which requires the sample to be cooled to temperatures of a few Kelvin or below. Here, we use a mechanically isolated quantum emitter in hexagonal boron nitride to explore the individual mechanisms which affect the coherence of an optical transition under resonant drive. We operate the system at the threshold where the mechanical isolation collapses in order to study the onset and temperature-dependence of dephasing and independently of spectral diffusion. The insights on the underlying physical decoherence mechanisms reveal a limit in temperature until which coherent driving of the system is possible. This study enables to increase the operation temperature of hBN-based quantum devices, therefore reducing the need for cryogenic cooling. The coherent control of a two-level system is at the core of quantum devices and understanding decoherence mechanisms is crucial for increasing their operating temperatures. Here, a mechanically isolated quantum emitter in hexagonal boron nitride is used to explore the individual mechanisms affecting the coherence of an optical transition under resonant drive.
{"title":"Probing the limits for coherent optical control of a mechanically decoupled defect center in hexagonal boron nitride","authors":"Michael K. Koch, Vibhav Bharadwaj, Alexander Kubanek","doi":"10.1038/s43246-024-00686-y","DOIUrl":"10.1038/s43246-024-00686-y","url":null,"abstract":"The coherent control of a two-level system is among the most essential challenges in modern quantum optics. Understanding its fundamental limitations is crucial, also for the realization of next generation quantum devices. The quantum coherence of a two-level system is fragile in particular, when the two levels are connected via an optical transition, which, at the same time, enables the manipulation of the system. When such quantum emitters are located in solids the coherence suffers from the interaction of the optical transition with the solid state environment, which requires the sample to be cooled to temperatures of a few Kelvin or below. Here, we use a mechanically isolated quantum emitter in hexagonal boron nitride to explore the individual mechanisms which affect the coherence of an optical transition under resonant drive. We operate the system at the threshold where the mechanical isolation collapses in order to study the onset and temperature-dependence of dephasing and independently of spectral diffusion. The insights on the underlying physical decoherence mechanisms reveal a limit in temperature until which coherent driving of the system is possible. This study enables to increase the operation temperature of hBN-based quantum devices, therefore reducing the need for cryogenic cooling. The coherent control of a two-level system is at the core of quantum devices and understanding decoherence mechanisms is crucial for increasing their operating temperatures. Here, a mechanically isolated quantum emitter in hexagonal boron nitride is used to explore the individual mechanisms affecting the coherence of an optical transition under resonant drive.","PeriodicalId":10589,"journal":{"name":"Communications Materials","volume":" ","pages":"1-7"},"PeriodicalIF":7.5,"publicationDate":"2024-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s43246-024-00686-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142574235","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Domain walls (DWs) in magnetic materials host various interesting magneto-transport phenomena. Recent theoretical proposals focusing on DWs of magnetic Weyl semimetals (mWSMs) suggest the emergence of even more exotic transport owing to topologically protected Weyl domains with opposite chirality. However, techniques for controlling and characterizing DWs in mWSMs have not yet matured sufficiently to identify the distinct features of electrical conduction on DWs. Here, by adopting an optical technique to manipulate magnetic domains in mWSM Co3Sn2S2 Hall-bar devices, we discover giant antisymmetric magnetoresistance arising across a DW formed by serially connected upward- and downward-magnetized Weyl domains. This phenomenon originates from the large tangent of the Hall angle associated with the intrinsic anomalous Hall effect in the oppositely magnetized Weyl domains. Furthermore, we quantitatively evaluate DW resistance by systematically controlling the number of DWs. These results underscore the promising avenue of Weyl DW engineering for advanced research on topological magnets. Domain walls in magnetic Weyl semimetals are a source of exotic transport owing to topologically protected domains with opposite chirality. Here, utilizing an optical technique to manipulate magnetic domains in Co3Sn2S2 Hall-bar devices, the authors discover giant antisymmetric magnetoresistance across a domain wall formed by serially connected upward- and downward-magnetized Weyl domains.
{"title":"Giant antisymmetric magnetoresistance arising across optically controlled domain walls in the magnetic Weyl semimetal Co3Sn2S2","authors":"Kohei Fujiwara, Kazuma Ogawa, Naotaka Yoshikawa, Koji Kobayashi, Kentaro Nomura, Ryo Shimano, Atsushi Tsukazaki","doi":"10.1038/s43246-024-00688-w","DOIUrl":"10.1038/s43246-024-00688-w","url":null,"abstract":"Domain walls (DWs) in magnetic materials host various interesting magneto-transport phenomena. Recent theoretical proposals focusing on DWs of magnetic Weyl semimetals (mWSMs) suggest the emergence of even more exotic transport owing to topologically protected Weyl domains with opposite chirality. However, techniques for controlling and characterizing DWs in mWSMs have not yet matured sufficiently to identify the distinct features of electrical conduction on DWs. Here, by adopting an optical technique to manipulate magnetic domains in mWSM Co3Sn2S2 Hall-bar devices, we discover giant antisymmetric magnetoresistance arising across a DW formed by serially connected upward- and downward-magnetized Weyl domains. This phenomenon originates from the large tangent of the Hall angle associated with the intrinsic anomalous Hall effect in the oppositely magnetized Weyl domains. Furthermore, we quantitatively evaluate DW resistance by systematically controlling the number of DWs. These results underscore the promising avenue of Weyl DW engineering for advanced research on topological magnets. Domain walls in magnetic Weyl semimetals are a source of exotic transport owing to topologically protected domains with opposite chirality. Here, utilizing an optical technique to manipulate magnetic domains in Co3Sn2S2 Hall-bar devices, the authors discover giant antisymmetric magnetoresistance across a domain wall formed by serially connected upward- and downward-magnetized Weyl domains.","PeriodicalId":10589,"journal":{"name":"Communications Materials","volume":" ","pages":"1-6"},"PeriodicalIF":7.5,"publicationDate":"2024-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s43246-024-00688-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142574231","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-31DOI: 10.1038/s43246-024-00683-1
Igor Konyashin, Ruslan Muydinov, Antonio Cammarata, Andrey Bondarev, Marin Rusu, Athanasios Koliogiorgos, Tomáš Polcar, Daniel Twitchen, Pierre-Olivier Colard, Bernd Szyszka, Nicola Palmer
{"title":"Author Correction: Face-centered cubic carbon as a fourth basic carbon allotrope with properties of intrinsic semiconductors and ultra-wide bandgap","authors":"Igor Konyashin, Ruslan Muydinov, Antonio Cammarata, Andrey Bondarev, Marin Rusu, Athanasios Koliogiorgos, Tomáš Polcar, Daniel Twitchen, Pierre-Olivier Colard, Bernd Szyszka, Nicola Palmer","doi":"10.1038/s43246-024-00683-1","DOIUrl":"10.1038/s43246-024-00683-1","url":null,"abstract":"","PeriodicalId":10589,"journal":{"name":"Communications Materials","volume":" ","pages":"1-1"},"PeriodicalIF":7.5,"publicationDate":"2024-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s43246-024-00683-1.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142574248","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-24DOI: 10.1038/s43246-024-00675-1
Xiangtao Zou, Takahiro Watanabe, Haru Kimata, Dong Xue, Ai Shimazaki, Minh Anh Truong, Atsushi Wakamiya, Kazuhiro Marumoto
Perovskite solar cells have attracted much attention as next-generation solar cells. However, a typical hole-transport material, spiro-OMeTAD, has associated difficulties including tedious synthesis and high cost. To overcome these shortcomings, an easily synthesized and low-cost hole-transport material has been developed: HND-2NOMe. Although HND-2NOMe has high local charge mobility because of the quasi-planar structure, its lower device performance is a weak point, the cause of which has not yet been clarified. Here, we analyse the source of the lower performance by clarifying the internal states from a microscopic viewpoint using electron spin resonance. We observe hole diffusion from perovskite to HND-2NOMe under dark conditions, indicating hole barrier formation at the perovskite/HND-2NOMe interface, leading to lower performance. Although such a barrier is formed, less hole accumulation for the HND-2NOMe-based cells under solar irradiation occurs, which is related to the stable performance. The sources of the lower but stable performance are crucially important for providing guidelines for improving the device performance. Hole-transport materials possessing high charge mobility are important in perovskite solar cells but the source of lower performance remains a mystery. Here, the microscopic mechanism for low but stable perovskite solar cell performance using these materials is analysed using electron spin resonance.
{"title":"Microscopic analysis of low but stable perovskite solar cell device performance using electron spin resonance","authors":"Xiangtao Zou, Takahiro Watanabe, Haru Kimata, Dong Xue, Ai Shimazaki, Minh Anh Truong, Atsushi Wakamiya, Kazuhiro Marumoto","doi":"10.1038/s43246-024-00675-1","DOIUrl":"10.1038/s43246-024-00675-1","url":null,"abstract":"Perovskite solar cells have attracted much attention as next-generation solar cells. However, a typical hole-transport material, spiro-OMeTAD, has associated difficulties including tedious synthesis and high cost. To overcome these shortcomings, an easily synthesized and low-cost hole-transport material has been developed: HND-2NOMe. Although HND-2NOMe has high local charge mobility because of the quasi-planar structure, its lower device performance is a weak point, the cause of which has not yet been clarified. Here, we analyse the source of the lower performance by clarifying the internal states from a microscopic viewpoint using electron spin resonance. We observe hole diffusion from perovskite to HND-2NOMe under dark conditions, indicating hole barrier formation at the perovskite/HND-2NOMe interface, leading to lower performance. Although such a barrier is formed, less hole accumulation for the HND-2NOMe-based cells under solar irradiation occurs, which is related to the stable performance. The sources of the lower but stable performance are crucially important for providing guidelines for improving the device performance. Hole-transport materials possessing high charge mobility are important in perovskite solar cells but the source of lower performance remains a mystery. Here, the microscopic mechanism for low but stable perovskite solar cell performance using these materials is analysed using electron spin resonance.","PeriodicalId":10589,"journal":{"name":"Communications Materials","volume":" ","pages":"1-12"},"PeriodicalIF":7.5,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s43246-024-00675-1.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142574193","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A strong coupling between electric polarization and elastic deformation in solids is an important factor in creating useful electromechanical nanodevices. Such coupling is typically allowed in insulating materials with inversion symmetry breaking as exemplified by the piezoelectric effect in ferroelectric materials. Therefore, materials with metallicity and centrosymmetry have tended to be out of scope in this perspective. Here, we report the observation of giant elastic deformation by the application of an alternating electric current in topological semimetals (V,Mo)Te2, regardless of the centrosymmetry. Considering the crystal and band structures and the asymmetric measurement configurations in addition to the absence of the electromechanical effect in a trivial semimetal TiTe2, the observed effect is discussed in terms of a Berry-phase-derived converse flexoelectric effect in metals. The observation of the flexoelectric effect in topological semimetals paves a way for a new type of nanoscale electromechanical sensors and energy harvesting. A strong coupling between electric polarization and elastic deformation is important for creating electromechanical nanodevices, but such coupling typically requires inversion symmetry breaking and is elusive in metals. Here, a current-induced giant elastic deformation is reported in topological semimetals VTe2 and MoTe2, regardless of centrosymmetry, due to the Berry phase enhancement of the flexoelectric response.
{"title":"Observation of converse flexoelectric effect in topological semimetals","authors":"Hidefumi Takahashi, Yusuke Kurosaka, Kenta Kimura, Akitoshi Nakano, Shintaro Ishiwata","doi":"10.1038/s43246-024-00677-z","DOIUrl":"10.1038/s43246-024-00677-z","url":null,"abstract":"A strong coupling between electric polarization and elastic deformation in solids is an important factor in creating useful electromechanical nanodevices. Such coupling is typically allowed in insulating materials with inversion symmetry breaking as exemplified by the piezoelectric effect in ferroelectric materials. Therefore, materials with metallicity and centrosymmetry have tended to be out of scope in this perspective. Here, we report the observation of giant elastic deformation by the application of an alternating electric current in topological semimetals (V,Mo)Te2, regardless of the centrosymmetry. Considering the crystal and band structures and the asymmetric measurement configurations in addition to the absence of the electromechanical effect in a trivial semimetal TiTe2, the observed effect is discussed in terms of a Berry-phase-derived converse flexoelectric effect in metals. The observation of the flexoelectric effect in topological semimetals paves a way for a new type of nanoscale electromechanical sensors and energy harvesting. A strong coupling between electric polarization and elastic deformation is important for creating electromechanical nanodevices, but such coupling typically requires inversion symmetry breaking and is elusive in metals. Here, a current-induced giant elastic deformation is reported in topological semimetals VTe2 and MoTe2, regardless of centrosymmetry, due to the Berry phase enhancement of the flexoelectric response.","PeriodicalId":10589,"journal":{"name":"Communications Materials","volume":" ","pages":"1-6"},"PeriodicalIF":7.5,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s43246-024-00677-z.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142574272","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Van der Waals (vdW) two-dimensional (2D) materials have unleashed unprecedented opportunities to probe emerging physics that could be potential candidates for various functional applications. In particular, vdW 2D magnetic materials exhibit significant potential for advanced spintronic devices. Recently, Fe3GaTe2 has been discovered to possess the room-temperature ferromagnetic property with an intrinsic perpendicular magnetic anisotropy (PMA). Furthermore, considerably large anomalous Hall and Nernst angles have been reported recently. These groundbreaking findings pave the way for significant advances in high density random-access memory as well as energy harvesting devices based on spin conversion. Enhancements in the PMA and Curie temperature contribute to improved performance with reliable operation in a wide temperature range above room temperature. Moreover, the exploration of giant anomalous Hall and Nernst angles is a crucial factor for the efficient operation of spintronic devices. In this study, we demonstrate that the application of pressure to the Fe3GaTe2 2D ferromagnetic film strengthens the interlayer coupling, resulting in an improved PMA property. In addition, the application of pressure has been found to significantly increase the anomalous Hall angle. Our findings suggest that the application of pressure effectively controls the vdW interlayer coupling, thereby manipulating the ferromagnetic and spin-conversion properties of the 2D materials. Van der Waals 2D magnetic materials are promising for spintronic devices due to their tunable large anomalous Hall and Nernst angles. Here, the magneto-transport properties of Fe3GaTe2 films are investigated under pressure, demonstrating a robust perpendicular magnetic anisotropy at room temperature and an enhancement of the anomalous Hall angle.
{"title":"Substantial enhancement of perpendicular magnetic anisotropy in van der Waals ferromagnetic Fe3GaTe2 film due to pressure application","authors":"Riku Iimori, Shaojie Hu, Akihiro Mitsuda, Takashi Kimura","doi":"10.1038/s43246-024-00665-3","DOIUrl":"10.1038/s43246-024-00665-3","url":null,"abstract":"Van der Waals (vdW) two-dimensional (2D) materials have unleashed unprecedented opportunities to probe emerging physics that could be potential candidates for various functional applications. In particular, vdW 2D magnetic materials exhibit significant potential for advanced spintronic devices. Recently, Fe3GaTe2 has been discovered to possess the room-temperature ferromagnetic property with an intrinsic perpendicular magnetic anisotropy (PMA). Furthermore, considerably large anomalous Hall and Nernst angles have been reported recently. These groundbreaking findings pave the way for significant advances in high density random-access memory as well as energy harvesting devices based on spin conversion. Enhancements in the PMA and Curie temperature contribute to improved performance with reliable operation in a wide temperature range above room temperature. Moreover, the exploration of giant anomalous Hall and Nernst angles is a crucial factor for the efficient operation of spintronic devices. In this study, we demonstrate that the application of pressure to the Fe3GaTe2 2D ferromagnetic film strengthens the interlayer coupling, resulting in an improved PMA property. In addition, the application of pressure has been found to significantly increase the anomalous Hall angle. Our findings suggest that the application of pressure effectively controls the vdW interlayer coupling, thereby manipulating the ferromagnetic and spin-conversion properties of the 2D materials. Van der Waals 2D magnetic materials are promising for spintronic devices due to their tunable large anomalous Hall and Nernst angles. Here, the magneto-transport properties of Fe3GaTe2 films are investigated under pressure, demonstrating a robust perpendicular magnetic anisotropy at room temperature and an enhancement of the anomalous Hall angle.","PeriodicalId":10589,"journal":{"name":"Communications Materials","volume":" ","pages":"1-7"},"PeriodicalIF":7.5,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s43246-024-00665-3.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142574230","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-21DOI: 10.1038/s43246-024-00676-0
Martin Gutierrez-Amigo, Ðorđe Dangić, Chunyu Guo, Claudia Felser, Philip J. W. Moll, Maia G. Vergniory, Ion Errea
The charge-density wave (CDW) mechanism and resulting structure of the AV3Sb5 family of kagome metals has posed a puzzling challenge since their discovery four years ago. In fact, the lack of consensus on the origin and structure of the CDW hinders the understanding of the emerging phenomena. Here, by employing a non-perturbative treatment of anharmonicity from first-principles calculations, we reveal that the charge-density transition in CsV3Sb5 is driven by the large electron-phonon coupling of the material and that the melting of the CDW state is attributed to ionic entropy and lattice anharmonicity. The calculated transition temperature is in very good agreement with experiments, implying that soft mode physics are at the core of the charge-density wave transition. Contrary to the standard assumption associated with a pure kagome lattice, the CDW is essentially three-dimensional as it is triggered by an unstable phonon at the L point. The absence of involvement of phonons at the M point enables us to constrain the resulting symmetries to six possible space groups. The unusually large electron-phonon linewidth of the soft mode explains why inelastic scattering experiments did not observe any softened phonon. We foresee that large anharmonic effects are ubiquitous and could be fundamental to understand the observed phenomena also in other kagome families. The charge-density wave state in AV3Sb5 kagome metals is intimately related to several unconventional and intriguing phenomena, but its origin and structure are still under debate. Here, non-perturbative calculations indicate a large electron-phonon coupling as the driving mechanism, attributing the melting of the charge-density wave state to ionic entropy and lattice anharmonicity.
自四年前发现 AV3Sb5 卡戈米金属家族以来，其电荷密度波（CDW）机制和由此产生的结构一直是一个令人费解的难题。事实上，对电荷密度波的起源和结构缺乏共识阻碍了人们对这一新现象的理解。在这里，我们利用第一原理计算中的非微扰处理非谐波性，揭示了 CsV3Sb5 中的电荷密度转变是由材料的大电子-声子耦合驱动的，而 CDW 状态的熔化则归因于离子熵和晶格非谐波性。计算得出的转变温度与实验结果非常吻合，这意味着软模式物理是电荷密度波转变的核心。与纯卡格姆晶格的标准假设相反，电荷密度波本质上是三维的，因为它是由 L 点的不稳定声子引发的。由于 M 点没有声子的参与，我们得以将由此产生的对称性限制在六个可能的空间群内。软模式异常巨大的电子-声子线宽解释了为什么非弹性散射实验没有观察到任何软化声子。我们预见到大的非谐波效应无处不在，而且可能是理解其他神户系中所观察到的现象的基础。AV3Sb5 kagome 金属中的电荷密度波态与几种非常规和有趣的现象密切相关，但其起源和结构仍存在争议。在这里，非微扰计算表明电子-声子耦合是驱动机制，电荷密度波态的熔化归因于离子熵和晶格非谐性。
{"title":"Phonon collapse and anharmonic melting of the 3D charge-density wave in kagome metals","authors":"Martin Gutierrez-Amigo, Ðorđe Dangić, Chunyu Guo, Claudia Felser, Philip J. W. Moll, Maia G. Vergniory, Ion Errea","doi":"10.1038/s43246-024-00676-0","DOIUrl":"10.1038/s43246-024-00676-0","url":null,"abstract":"The charge-density wave (CDW) mechanism and resulting structure of the AV3Sb5 family of kagome metals has posed a puzzling challenge since their discovery four years ago. In fact, the lack of consensus on the origin and structure of the CDW hinders the understanding of the emerging phenomena. Here, by employing a non-perturbative treatment of anharmonicity from first-principles calculations, we reveal that the charge-density transition in CsV3Sb5 is driven by the large electron-phonon coupling of the material and that the melting of the CDW state is attributed to ionic entropy and lattice anharmonicity. The calculated transition temperature is in very good agreement with experiments, implying that soft mode physics are at the core of the charge-density wave transition. Contrary to the standard assumption associated with a pure kagome lattice, the CDW is essentially three-dimensional as it is triggered by an unstable phonon at the L point. The absence of involvement of phonons at the M point enables us to constrain the resulting symmetries to six possible space groups. The unusually large electron-phonon linewidth of the soft mode explains why inelastic scattering experiments did not observe any softened phonon. We foresee that large anharmonic effects are ubiquitous and could be fundamental to understand the observed phenomena also in other kagome families. The charge-density wave state in AV3Sb5 kagome metals is intimately related to several unconventional and intriguing phenomena, but its origin and structure are still under debate. Here, non-perturbative calculations indicate a large electron-phonon coupling as the driving mechanism, attributing the melting of the charge-density wave state to ionic entropy and lattice anharmonicity.","PeriodicalId":10589,"journal":{"name":"Communications Materials","volume":" ","pages":"1-8"},"PeriodicalIF":7.5,"publicationDate":"2024-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s43246-024-00676-0.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142574196","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Segregation channels with misoriented spurious grains, known as freckles, are an unacceptable casting defect in superalloy turbine blades. A digital-twin method to predict segregation channels was proposed in our previous studies; however, the formation of spurious grains was ignored. Here, we extend the digital twin methodology by incorporating dendrite fragmentation, which is recognized as the predominant mechanism in the formation of spurious grains. The flow-induced fragmentation process has been refined to account for the timing of dendrite pinch-off. A three-phase mixed columnar-equiaxed solidification model was used to track the motion of the crystal fragments. Directional solidification experiments for superalloy casting were conducted in an industrial-scale Bridgman furnace, and the distribution of spurious grains in the freckles was metallographically analysed. Excellent simulation-experiment-agreement was achieved. Based on this study, the formation of spurious grains within the segregation channels is mainly caused by the flow-driven fragmentation mechanism. Experimentally measured freckles can be reproduced only if the timing of the dendrite pinch-off is considered. Defect-free castings are vital to the structural integrity of superalloys used in aerospace. Here, a digital twin method is developed for modelling spurious grain formation and segregation channels in directionally solidified superalloys.
{"title":"Modelling freckles and spurious grain formation in directionally solidified superalloy castings","authors":"Haijie Zhang, Yunxing Zhao, Wei Xiong, Dexin Ma, Andreas Ludwig, Abdellah Kharicha, Menghuai Wu","doi":"10.1038/s43246-024-00672-4","DOIUrl":"10.1038/s43246-024-00672-4","url":null,"abstract":"Segregation channels with misoriented spurious grains, known as freckles, are an unacceptable casting defect in superalloy turbine blades. A digital-twin method to predict segregation channels was proposed in our previous studies; however, the formation of spurious grains was ignored. Here, we extend the digital twin methodology by incorporating dendrite fragmentation, which is recognized as the predominant mechanism in the formation of spurious grains. The flow-induced fragmentation process has been refined to account for the timing of dendrite pinch-off. A three-phase mixed columnar-equiaxed solidification model was used to track the motion of the crystal fragments. Directional solidification experiments for superalloy casting were conducted in an industrial-scale Bridgman furnace, and the distribution of spurious grains in the freckles was metallographically analysed. Excellent simulation-experiment-agreement was achieved. Based on this study, the formation of spurious grains within the segregation channels is mainly caused by the flow-driven fragmentation mechanism. Experimentally measured freckles can be reproduced only if the timing of the dendrite pinch-off is considered. Defect-free castings are vital to the structural integrity of superalloys used in aerospace. Here, a digital twin method is developed for modelling spurious grain formation and segregation channels in directionally solidified superalloys.","PeriodicalId":10589,"journal":{"name":"Communications Materials","volume":" ","pages":"1-12"},"PeriodicalIF":7.5,"publicationDate":"2024-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11489085/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142459884","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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