The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Yoshio Miura - One of the best experts on this subject based on the ideXlab platform.
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first principles study of the anisotropic magneto peltier effect
Physical Review B, 2019Co-Authors: Keisuke Masuda, Ryo Iguchi, Ken-ichi Uchida, Yoshio MiuraAbstract:We study theoretically the anisotropic magneto-Peltier effect, which was recently demonstrated experimentally. A first-principles-based Boltzmann transport approach including the spin-orbit interaction shows that Ni has a larger anisotropy of the Peltier coefficient ($\Delta \Pi$) than Fe, consistent with experiments. It is clarified that spin-flip electron transitions due to the spin-orbit interaction are the key in the mechanism of the large anisotropic magneto-Peltier effect. Using our method, we further predict several ferromagnetic metals with much larger $\Delta \Pi$ than that of Ni.
Keisuke Masuda - One of the best experts on this subject based on the ideXlab platform.
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first principles study of the anisotropic magneto peltier effect
Physical Review B, 2019Co-Authors: Keisuke Masuda, Ryo Iguchi, Ken-ichi Uchida, Yoshio MiuraAbstract:We study theoretically the anisotropic magneto-Peltier effect, which was recently demonstrated experimentally. A first-principles-based Boltzmann transport approach including the spin-orbit interaction shows that Ni has a larger anisotropy of the Peltier coefficient ($\Delta \Pi$) than Fe, consistent with experiments. It is clarified that spin-flip electron transitions due to the spin-orbit interaction are the key in the mechanism of the large anisotropic magneto-Peltier effect. Using our method, we further predict several ferromagnetic metals with much larger $\Delta \Pi$ than that of Ni.
Torreggiani Ambra - One of the best experts on this subject based on the ideXlab platform.
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Punti Critici nella Progettazione di Macchine Sincrone ad Alte Prestazioni
Università degli studi di Modena e Reggio Emilia, 2020Co-Authors: Torreggiani AmbraAbstract:L’interesse per le macchine elettriche sincrone a magneti permanenti o a riluttanza pura è cresciuto esponenzialmente negli ultimi anni. Questo trend è effetto di un insieme di fattori: l’evoluzione tecnologica e una maggiore attenzione alle tematiche ambientali per la riduzione dei gas a effetto serra e un’economia eco-sostenibile. La diffusione delle macchine elettriche nell'industria, nei trasporti e nell'uso domestico potrebbe essere suddivisa in due tipologie: • Elettrificazione, cioè il passaggio da tecnologie tradizionali basate su fonti non rinnovabili, a sistemi ibridi o completamente elettrici (full electric); • Passaggio da macchine elettriche basate su vecchie tecnologie poco efficienti a macchine elettriche più efficienti. Il processo di elettrificazione trova il suo massimo esponente nell'industria dell’automotive assieme agli altri settori dei trasporti e.g. ferroviario, aeronautico, etc. Circa il 50% dell’energia elettrica mondiale è convertita da motori elettrici, di cui circa l’80% sono basati su vecchie tecnologie affidabili, ma meno efficienti. Sotto la spinta delle normative internazionali e delle direttive europee molte aziende stanno sostituendo di questi motori con altri più efficienti o che presentano vantaggi dal punto di vista del controllo. Il contributo sviluppato in questa tesi di ricerca è focalizzato nel definire metodi di design delle macchine elettriche sincrone con l’obiettivo di migliorarne prestazioni, affidabilità e robustezza al guasto. A tal scopo il lavoro di tesi si è concentrato su alcuni aspetti fondamentali. Il primo è stato lo studio di metodi di ottimizzazione del design della macchina comprensivi dei tipici difetti di produzione anche in condizioni di macchina sana. Lo scopo è stato studiare gli effetti sulle performance, per migliorare affidabilità e robustezza alle imperfezioni. A questo, è seguita una ricerca sulla demagnetizzazione delle macchine a magneti permanenti superficiali con particolare attenzione alle correnti parassite nei magneti. Il risultato dell’attività è un nuovo design del rotore a magneti permanenti interni di cui sono stati realizzati e testati alcuni prototipi. L’ultimo tema ha riguardato la capacità di resistenza al guasto di una macchina sincrona a riluttanza pura avente due avvolgimenti trifase indipendenti alimentanti da due inverter. La geometria della macchina è stata ottimizzata rispetto a condizioni ottimali e di guasto; la geometria con prestazioni al guasto migliori è stata scelta per analizzarne le prestazioni rispetto diversi parametri sia in condizioni ottimali che di guasto di uno dei due avvolgimenti.The interest in permanent-magnets or pure reluctance synchronous machines has increased rapidly in the last years. This trend is a combination of factors: the technological progress and a closer attention to environmental issues to reduce greenhouse gas emissions and to support a green economy. The diffusion of electrical machines in the industrial industry, transports and household appliances could be split in two types: • Electrification, that means chancing the technologies relying on non-renewable sources with hybrid or full electric systems; • The transition from electrical machines based on traditional technologies, but less efficient, to more efficient electrical machines. The automotive is major industry of the electrification process followed to the other transportation industries e.g. railways, aircraft, etc. The 50% of global electric energy is converted in electric motor of which the 80% relies on traditional technologies. These motors are reliable, but less efficient. As a consequence, many companies are adopting more efficient motors or more convenient ones from a control point of view under the pressure of International Standards and European Directives. The contribution of this thesis is developing design methods of synchronous electrical machines with the aim to improve their performance, reliability and fault-tolerant capability. For that purpose, the research activity has focused on some fundamental issues. The first topic is the study of optimization machine design methods inclusive of typical manufacturing defects even in healthy machine conditions. The aim is analyzing the defect influence on performance and improving machine reliability and robustness. After this study, it is followed a research on the demagnetization issue of surface permanent-magnet machines with a special consideration of magnets eddy currents. The activity result is a new design of internal permanent-magnet rotor which has prototyped and tested. The last topic is a study of fault-tolerant capability of a pure reluctance synchronous machine with two independent three-phase windings fed by two inverters. The machine geometry has optimized according to both optimal and fault conditions; the design with the best performance in fault conditions has been chosen and it has been analyzed with respect to different parameters in healthy condition and with one faulty winding
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Punti Critici nella Progettazione di Macchine Sincrone ad Alte Prestazioni
Università degli studi di Modena e Reggio Emilia, 2020Co-Authors: Torreggiani AmbraAbstract:L\u2019interesse per le macchine elettriche sincrone a magneti permanenti o a riluttanza pura \ue8 cresciuto esponenzialmente negli ultimi anni. Questo trend \ue8 effetto di un insieme di fattori: l\u2019evoluzione tecnologica e una maggiore attenzione alle tematiche ambientali per la riduzione dei gas a effetto serra e un\u2019economia eco-sostenibile. La diffusione delle macchine elettriche nell'industria, nei trasporti e nell'uso domestico potrebbe essere suddivisa in due tipologie: \u2022 Elettrificazione, cio\ue8 il passaggio da tecnologie tradizionali basate su fonti non rinnovabili, a sistemi ibridi o completamente elettrici (full electric); \u2022 Passaggio da macchine elettriche basate su vecchie tecnologie poco efficienti a macchine elettriche pi\uf9 efficienti. Il processo di elettrificazione trova il suo massimo esponente nell'industria dell\u2019automotive assieme agli altri settori dei trasporti e.g. ferroviario, aeronautico, etc. Circa il 50% dell\u2019energia elettrica mondiale \ue8 convertita da motori elettrici, di cui circa l\u201980% sono basati su vecchie tecnologie affidabili, ma meno efficienti. Sotto la spinta delle normative internazionali e delle direttive europee molte aziende stanno sostituendo di questi motori con altri pi\uf9 efficienti o che presentano vantaggi dal punto di vista del controllo. Il contributo sviluppato in questa tesi di ricerca \ue8 focalizzato nel definire metodi di design delle macchine elettriche sincrone con l\u2019obiettivo di migliorarne prestazioni, affidabilit\ue0 e robustezza al guasto. A tal scopo il lavoro di tesi si \ue8 concentrato su alcuni aspetti fondamentali. Il primo \ue8 stato lo studio di metodi di ottimizzazione del design della macchina comprensivi dei tipici difetti di produzione anche in condizioni di macchina sana. Lo scopo \ue8 stato studiare gli effetti sulle performance, per migliorare affidabilit\ue0 e robustezza alle imperfezioni. A questo, \ue8 seguita una ricerca sulla demagnetizzazione delle macchine a magneti permanenti superficiali con particolare attenzione alle correnti parassite nei magneti. Il risultato dell\u2019attivit\ue0 \ue8 un nuovo design del rotore a magneti permanenti interni di cui sono stati realizzati e testati alcuni prototipi. L\u2019ultimo tema ha riguardato la capacit\ue0 di resistenza al guasto di una macchina sincrona a riluttanza pura avente due avvolgimenti trifase indipendenti alimentanti da due inverter. La geometria della macchina \ue8 stata ottimizzata rispetto a condizioni ottimali e di guasto; la geometria con prestazioni al guasto migliori \ue8 stata scelta per analizzarne le prestazioni rispetto diversi parametri sia in condizioni ottimali che di guasto di uno dei due avvolgimenti.The interest in permanent-magnets or pure reluctance synchronous machines has increased rapidly in the last years. This trend is a combination of factors: the technological progress and a closer attention to environmental issues to reduce greenhouse gas emissions and to support a green economy. The diffusion of electrical machines in the industrial industry, transports and household appliances could be split in two types: \u2022 Electrification, that means chancing the technologies relying on non-renewable sources with hybrid or full electric systems; \u2022 The transition from electrical machines based on traditional technologies, but less efficient, to more efficient electrical machines. The automotive is major industry of the electrification process followed to the other transportation industries e.g. railways, aircraft, etc. The 50% of global electric energy is converted in electric motor of which the 80% relies on traditional technologies. These motors are reliable, but less efficient. As a consequence, many companies are adopting more efficient motors or more convenient ones from a control point of view under the pressure of International Standards and European Directives. The contribution of this thesis is developing design methods of synchronous electrical machines with the aim to improve their performance, reliability and fault-tolerant capability. For that purpose, the research activity has focused on some fundamental issues. The first topic is the study of optimization machine design methods inclusive of typical manufacturing defects even in healthy machine conditions. The aim is analyzing the defect influence on performance and improving machine reliability and robustness. After this study, it is followed a research on the demagnetization issue of surface permanent-magnet machines with a special consideration of magnets eddy currents. The activity result is a new design of internal permanent-magnet rotor which has prototyped and tested. The last topic is a study of fault-tolerant capability of a pure reluctance synchronous machine with two independent three-phase windings fed by two inverters. The machine geometry has optimized according to both optimal and fault conditions; the design with the best performance in fault conditions has been chosen and it has been analyzed with respect to different parameters in healthy condition and with one faulty winding
Ilya Belopolski - One of the best experts on this subject based on the ideXlab platform.
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discovery of topological weyl fermion lines and drumhead surface states in a room temperature magnet
arXiv: Materials Science, 2020Co-Authors: Ilya Belopolski, Kaustuv Manna, Daniel S Sanchez, Guoqing Chang, Benedikt Ernst, Jiaxin Yin, Songtian S Zhang, Tyler A Cochran, Nana Shumiya, Hao ZhengAbstract:Topological matter is known to exhibit unconventional surface states and anomalous transport owing to unusual bulk electronic topology. In this study, we use photoemission spectroscopy and quantum transport to elucidate the topology of the room temperature magnet Co$_2$MnGa. We observe sharp bulk Weyl fermion line dispersions indicative of nontrivial topological invariants present in the magnetic phase. On the surface of the magnet, we observe electronic wave functions that take the form of drumheads, enabling us to directly visualize the crucial components of the bulk-boundary topological correspondence. By considering the Berry curvature field associated with the observed topological Weyl fermion lines, we quantitatively account for the giant anomalous Hall response observed in our samples. Our experimental results suggest a rich interplay of strongly correlated electrons and topology in this quantum magnet.
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discovery of topological weyl fermion lines and drumhead surface states in a room temperature magnet
Science, 2019Co-Authors: Ilya Belopolski, Kaustuv Manna, Daniel S Sanchez, Guoqing Chang, Benedikt Ernst, Jiaxin Yin, Songtian S Zhang, Tyler A Cochran, Nana Shumiya, Hao ZhengAbstract:Topological matter is known to exhibit unconventional surface states and anomalous transport owing to unusual bulk electronic topology. In this study, we use photoemission spectroscopy and quantum transport to elucidate the topology of the room temperature magnet Co2MnGa. We observe sharp bulk Weyl fermion line dispersions indicative of nontrivial topological invariants present in the magnetic phase. On the surface of the magnet, we observe electronic wave functions that take the form of drumheads, enabling us to directly visualize the crucial components of the bulk-boundary topological correspondence. By considering the Berry curvature field associated with the observed topological Weyl fermion lines, we quantitatively account for the giant anomalous Hall response observed in this magnet. Our experimental results suggest a rich interplay of strongly interacting electrons and topology in quantum matter.
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signatures of the adler bell jackiw chiral anomaly in a weyl fermion semimetal
Nature Communications, 2016Co-Authors: Cheng Long Zhang, Ilya Belopolski, Zhujun Yuan, Ziquan Lin, Bingbing Tong, Guang Bian, Nasser Alidoust, Chicheng Lee, Shinming Huang, Tay Rong ChangAbstract:Weyl semimetals provide the realization of Weyl fermions in solid-state physics. Among all the physical phenomena that are enabled by Weyl semimetals, the chiral anomaly is the most unusual one. Here, we report signatures of the chiral anomaly in the Magneto-Transport measurements on the first Weyl semimetal TaAs. We show negative magnetoresistance under parallel electric and magnetic fields, that is, unlike most metals whose resistivity increases under an external magnetic field, we observe that our high mobility TaAs samples become more conductive as a magnetic field is applied along the direction of the current for certain ranges of the field strength. We present systematically detailed data and careful analyses, which allow us to exclude other possible origins of the observed negative magnetoresistance. Our transport data, corroborated by photoemission measurements, first-principles calculations and theoretical analyses, collectively demonstrate signatures of the Weyl fermion chiral anomaly in the Magneto-Transport of TaAs.
Philip Kim - One of the best experts on this subject based on the ideXlab platform.
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Experimental observation of the quantum Hall effect and Berry's phase in graphene
Nature, 2005Co-Authors: Y.b. Zhang, Y. W. Tan, H L Stormer, Philip KimAbstract:When electrons are confined in two-dimensional materials, quantum-mechanically enhanced transport phenomena such as the quantum Hall effect can be observed. Graphene, consisting of an isolated single atomic layer of graphite, is an ideal realization of such a two-dimensional system. However, its behaviour is expected to differ markedly from the well-studied case of quantum wells in conventional semiconductor interfaces. This difference arises from the unique electronic properties of graphene, which exhibits electron - hole degeneracy and vanishing carrier mass near the point of charge neutrality(1,2). Indeed, a distinctive half-integer quantum Hall effect has been predicted(3-5) theoretically, as has the existence of a non-zero Berry's phase ( a geometric quantum phase) of the electron wavefunction - a consequence of the exceptional topology of the graphene band structure(6,7). Recent advances in micromechanical extraction and fabrication techniques for graphite structures(8-12) now permit such exotic two-dimensional electron systems to be probed experimentally. Here we report an experimental investigation of Magneto-Transport in a high-mobility single layer of graphene. Adjusting the chemical potential with the use of the electric field effect, we observe an unusual half-integer quantum Hall effect for both electron and hole carriers in graphene. The relevance of Berry's phase to these experiments is confirmed by magneto-oscillations. In addition to their purely scientific interest, these unusual quantum transport phenomena may lead to new applications in carbon-based electronic and magneto-electronic devices.