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Iron-based binary ferromagnets for transverse thermoelectric conversion 期刊论文
NATURE, 2020, 581 (7806) : 53-+
作者:  Grun, Rainer;  Pike, Alistair;  McDermott, Frank;  Eggins, Stephen;  Mortimer, Graham;  Aubert, Maxime;  Kinsley, Lesley;  Joannes-Boyau, Renaud;  Rumsey, Michael;  Denys, Christiane;  Brink, James;  Clark, Tara;  Stringer, Chris
收藏  |  浏览/下载:56/0  |  提交时间:2020/07/03

Aluminium- and gallium-doped iron compounds show a large anomalous Nernst effect owing to a topological electronic structure, and their films are potentially suitable for designing low-cost, flexible microelectronic thermoelectric generators.


Thermoelectric generation using the anomalous Nernst effect (ANE) has great potential for application in energy harvesting technology because the transverse geometry of the Nernst effect should enable efficient, large-area and flexible coverage of a heat source. For such applications to be viable, substantial improvements will be necessary not only for their performance but also for the associated material costs, safety and stability. In terms of the electronic structure, the anomalous Nernst effect (ANE) originates from the Berry curvature of the conduction electrons near the Fermi energy(1,2). To design a large Berry curvature, several approaches have been considered using nodal points and lines in momentum space(3-10). Here we perform a high-throughput computational search and find that 25 percent doping of aluminium and gallium in alpha iron, a naturally abundant and low-cost element, dramatically enhances the ANE by a factor of more than ten, reaching about 4 and 6 microvolts per kelvin at room temperature, respectively, close to the highest value reported so far. The comparison between experiment and theory indicates that the Fermi energy tuning to the nodal web-a flat band structure made of interconnected nodal lines-is the key for the strong enhancement in the transverse thermoelectric coefficient, reaching a value of about 5 amperes per kelvin per metre with a logarithmic temperature dependence. We have also succeeded in fabricating thin films that exhibit a large ANE at zero field, which could be suitable for designing low-cost, flexible microelectronic thermoelectric generators(11-13).


  
Spin current from sub-terahertz-generated antiferromagnetic magnons 期刊论文
NATURE, 2020, 578 (7793) : 70-+
作者:  Zemp, M.;  Huss, M.;  Thibert, E.;  Eckert, N.;  McNabb, R.;  Huber, J.;  Barandun, M.;  Machguth, H.;  Nussbaumer, S. U.;  Gartner-Roer, I.;  Thomson, L.;  Paul, F.;  Maussion, F.;  Kutuzov, S.;  Cogley, J. G.
收藏  |  浏览/下载:58/0  |  提交时间:2020/07/03

Pure spin currents are simultaneously generated and detected electrically through sub-terahertz magnons in the antiferromagnetic insulator Cr2O3, demonstrating the potential of magnon excitations in antiferromagnets for high-frequency spintronic devices.


Spin dynamics in antiferromagnets has much shorter timescales than in ferromagnets, offering attractive properties for potential applications in ultrafast devices(1-3). However, spin-current generation via antiferromagnetic resonance and simultaneous electrical detection by the inverse spin Hall effect in heavy metals have not yet been explicitly demonstrated(4-6). Here we report sub-terahertz spin pumping in heterostructures of a uniaxial antiferromagnetic Cr2O3 crystal and a heavy metal (Pt or Ta in its beta phase). At 0.240 terahertz, the antiferromagnetic resonance in Cr2O3 occurs at about 2.7 tesla, which excites only right-handed magnons. In the spin-canting state, another resonance occurs at 10.5 tesla from the precession of induced magnetic moments. Both resonances generate pure spin currents in the heterostructures, which are detected by the heavy metal as peaks or dips in the open-circuit voltage. The pure-spin-current nature of the electrically detected signals is unambiguously confirmed by the reversal of the voltage polarity observed under two conditions: when switching the detector metal from Pt to Ta, reversing the sign of the spin Hall angle(7-9), and when flipping the magnetic-field direction, reversing the magnon chirality(4,5). The temperature dependence of the electrical signals at both resonances suggests that the spin current contains both coherent and incoherent magnon contributions, which is further confirmed by measurements of the spin Seebeck effect and is well described by a phenomenological theory. These findings reveal the unique characteristics of magnon excitations in antiferromagnets and their distinctive roles in spin-charge conversion in the high-frequency regime.


  
Investigation of the fine structure of antihydrogen 期刊论文
NATURE, 2020, 578 (7795) : 375-+
作者:  Zhang, Bing;  Ma, Sai;  Rachmin, Inbal;  He, Megan;  Baral, Pankaj;  Choi, Sekyu;  Goncalves, William A.;  Shwartz, Yulia;  Fast, Eva M.;  Su, Yiqun;  Zon, Leonard I.;  Regev, Aviv;  Buenrostro, Jason D.;  Cunha, Thiago M.;  Chiu, Isaac M.;  Fisher, David E.;  Hsu, Ya-Chieh
收藏  |  浏览/下载:64/0  |  提交时间:2020/07/03

At the historic Shelter Island Conference on the Foundations of Quantum Mechanics in 1947, Willis Lamb reported an unexpected feature in the fine structure of atomic hydrogen: a separation of the 2S(1/2) and 2P(1/2) states(1). The observation of this separation, now known as the Lamb shift, marked an important event in the evolution of modern physics, inspiring others to develop the theory of quantum electrodynamics(2-5). Quantum electrodynamics also describes antimatter, but it has only recently become possible to synthesize and trap atomic antimatter to probe its structure. Mirroring the historical development of quantum atomic physics in the twentieth century, modern measurements on anti-atoms represent a unique approach for testing quantum electrodynamics and the foundational symmetries of the standard model. Here we report measurements of the fine structure in the n = 2 states of antihydrogen, the antimatter counterpart of the hydrogen atom. Using optical excitation of the 1S-2P Lyman-alpha transitions in antihydrogen(6), we determine their frequencies in a magnetic field of 1 tesla to a precision of 16 parts per billion. Assuming the standard Zeeman and hyperfine interactions, we infer the zero-field fine-structure splitting (2P(1/2)-2P(3/2)) in antihydrogen. The resulting value is consistent with the predictions of quantum electrodynamics to a precision of 2 per cent. Using our previously measured value of the 1S-2S transition frequency(6,7), we find that the classic Lamb shift in antihydrogen (2S(1/2)-2P(1/2) splitting at zero field) is consistent with theory at a level of 11 per cent. Our observations represent an important step towards precision measurements of the fine structure and the Lamb shift in the antihydrogen spectrum as tests of the charge-parity-time symmetry(8) and towards the determination of other fundamental quantities, such as the antiproton charge radius(9,10), in this antimatter system.


Precision measurements of the 1S-2P transition in antihydrogen that take into account the standard Zeeman and hyperfine effects confirm the predictions of quantum electrodynamics.


  
An Evaluation of Kolmogorov's-5/3 Power Law Observed Within the Turbulent Airflow Above the Ocean 期刊论文
GEOPHYSICAL RESEARCH LETTERS, 2019
作者:  Ortiz-Suslow, David G.;  Wang, Qing
收藏  |  浏览/下载:26/0  |  提交时间:2020/02/17
Kolmogorov'  s inertial subrange  turbulence  theory validation  marine atmospheric surface layer  air-sea interaction  field studies  
Investing in Climate Change Adaptation: Motivations and Green Incentives in the Fiji Islands 期刊论文
ECOLOGICAL ECONOMICS, 2018, 154: 394-408
作者:  Di Falco, Salvatore;  Sharma, Sindra
收藏  |  浏览/下载:16/0  |  提交时间:2019/04/09
Small Islands States  Adaptation  Investment  Theory of Planned Behavior  Experiment  Conditionality  Microloans  Framed Field Experiment  Psychology  
Tamm review: Tree interactions between myth and reality 期刊论文
FOREST ECOLOGY AND MANAGEMENT, 2018, 424: 164-176
作者:  Pommerening, Arne;  Meador, Andrew J. Sanchez
收藏  |  浏览/下载:19/0  |  提交时间:2019/04/09
Interaction  Facilitation  Competition  Mode of interaction  Tree mechanics  Stress-gradient hypothesis  Niche theory  Self thinning  Janzen-Connell  Herd immunity theories  Overyielding  Competition indices  Ecological field theory  Interaction kernels  Point process statistics  
Emotions predict policy support: Why it matters how people feel about climate change 期刊论文
GLOBAL ENVIRONMENTAL CHANGE-HUMAN AND POLICY DIMENSIONS, 2018, 50: 25-40
作者:  Wang, Susie;  Leviston, Zoe;  Hurlstone, Mark;  Lawrence, Carmen;  Walker, Lain
收藏  |  浏览/下载:20/0  |  提交时间:2019/04/09
Climate change  Emotion  Care  Identity  Field theory  Psychological distance