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Electrical manipulation of a topological antiferromagnetic state 期刊论文
NATURE, 2020, 580 (7805) : 608-+
作者:  Chabon, Jacob J.;  Hamilton, Emily G.;  Kurtz, David M.;  Esfahani, Mohammad S.;  Moding, Everett J.;  Stehr, Henning;  Schroers-Martin, Joseph;  Nabet, Barzin Y.;  Chen, Binbin;  Chaudhuri, Aadel A.;  Liu, Chih Long;  Hui, Angela B.;  Jin, Michael C.;  Azad, Tej D.;  Almanza, Diego;  Jeon, Young-Jun;  Nesselbush, Monica C.;  Keh, Lyron Co Ting;  Bonilla, Rene F.;  Yoo, Christopher H.;  Ko, Ryan B.;  Chen, Emily L.;  Merriott, David J.;  Massion, Pierre P.;  Mansfield, Aaron S.;  Jen, Jin;  Ren, Hong Z.;  Lin, Steven H.;  Costantino, Christina L.;  Burr, Risa;  Tibshirani, Robert;  Gambhir, Sanjiv S.;  Berry, Gerald J.;  Jensen, Kristin C.;  West, Robert B.;  Neal, Joel W.;  Wakelee, Heather A.;  Loo, Billy W., Jr.;  Kunder, Christian A.;  Leung, Ann N.;  Lui, Natalie S.;  Berry, Mark F.;  Shrager, Joseph B.;  Nair, Viswam S.;  Haber, Daniel A.;  Sequist, Lecia V.;  Alizadeh, Ash A.;  Diehn, Maximilian
收藏  |  浏览/下载:61/0  |  提交时间:2020/07/03

Room-temperature electrical switching of a topological antiferromagnetic state in polycrystalline Mn3Sn thin films is demonstrated using the same protocol as that used for conventional ferromagnetic metals.


Electrical manipulation of phenomena generated by nontrivial band topology is essential for the development of next-generation technology using topological protection. A Weyl semimetal is a three-dimensional gapless system that hosts Weyl fermions as low-energy quasiparticles(1-4). It has various exotic properties, such as a large anomalous Hall effect (AHE) and chiral anomaly, which are robust owing to the topologically protected Weyl nodes(1-16). To manipulate such phenomena, a magnetic version of Weyl semimetals would be useful for controlling the locations of Weyl nodes in the Brillouin zone. Moreover, electrical manipulation of antiferromagnetic Weyl metals would facilitate the use of antiferromagnetic spintronics to realize high-density devices with ultrafast operation(17,18). However, electrical control of a Weyl metal has not yet been reported. Here we demonstrate the electrical switching of a topological antiferromagnetic state and its detection by the AHE at room temperature in a polycrystalline thin film(19) of the antiferromagnetic Weyl metal Mn3Sn9,10,12,20, which exhibits zero-field AHE. Using bilayer devices composed of Mn3Sn and nonmagnetic metals, we find that an electrical current density of about 10(10) to 10(11) amperes per square metre induces magnetic switching in the nonmagnetic metals, with a large change in Hall voltage. In addition, the current polarity along the bias field and the sign of the spin Hall angle of the nonmagnetic metals-positive for Pt (ref. (21)), close to 0 for Cu and negative for W (ref. (22))-determines the sign of the Hall voltage. Notably, the electrical switching in the antiferromagnet is achieved with the same protocol as that used for ferromagnetic metals(23,24). Our results may lead to further scientific and technological advances in topological magnetism and antiferromagnetic spintronics.


  
Mott and generalized Wigner crystal states in WSe2/WS2 moire superlattices 期刊论文
NATURE, 2020, 579 (7799) : 359-+
作者:  Yuan, Jie;  Chang, Si-Yuan;  Yin, Shi-Gang;  Liu, Zhi-Yang;  Cheng, Xiu;  Liu, Xi-Juan;  Jiang, Qiang;  Gao, Ge;  Lin, De-Ying;  Kang, Xin-Lei;  Ye, Shi-Wei;  Chen, Zheng;  Yin, Jiang-An;  Hao, Pei;  Jiang, Lubin;  Cai, Shi-Qing
收藏  |  浏览/下载:79/0  |  提交时间:2020/07/03

Strongly correlated insulating Mott and generalized Wigner phases are detected in WSe2/WS2 moire superlattices, and their electrical properties and excited spin states are studied using an optical technique.


Moire superlattices can be used to engineer strongly correlated electronic states in two-dimensional van der Waals heterostructures, as recently demonstrated in the correlated insulating and superconducting states observed in magic-angle twisted-bilayer graphene and ABC trilayer graphene/boron nitride moire superlattices(1-4). Transition metal dichalcogenide moire heterostructures provide another model system for the study of correlated quantum phenomena(5) because of their strong light-matter interactions and large spin-orbit coupling. However, experimental observation of correlated insulating states in this system is challenging with traditional transport techniques. Here we report the optical detection of strongly correlated phases in semiconducting WSe2/WS2 moire superlattices. We use a sensitive optical detection technique and reveal a Mott insulator state at one hole per superlattice site and surprising insulating phases at 1/3 and 2/3 filling of the superlattice, which we assign to generalized Wigner crystallization on the underlying lattice(6-11). Furthermore, the spin-valley optical selection rules(12-14) of transition metal dichalcogenide heterostructures allow us to optically create and investigate low-energy excited spin states in the Mott insulator. We measure a very long spin relaxation lifetime of many microseconds in the Mott insulating state, orders of magnitude longer than that of charge excitations. Our studies highlight the value of using moire superlattices beyond graphene to explore correlated physics.


  
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:55/0  |  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.


  
Design and synthesis of multigrain nanocrystals via geometric misfit strain 期刊论文
NATURE, 2020, 577 (7790) : 359-+
作者:  Oh, Myoung Hwan;  Cho, Min Gee;  Chung, Dong Young;  Park, Inchul;  Kwon, Youngwook Paul;  Ophus, Colin;  Kim, Dokyoon;  Kim, Min Gyu;  Jeong, Beomgyun;  Gu, X. Wendy;  Jo, Jinwoung;  Yoo, Ji Mun;  Hong, Jaeyoung;  McMains, Sara;  Kang, Kisuk;  Sung, Yung-Eun;  Alivisatos, A. Paul;  Hyeon, Taeghwan
收藏  |  浏览/下载:34/0  |  提交时间:2020/07/03

The impact of topological defects associated with grain boundaries (GB defects) on the electrical, optical, magnetic, mechanical and chemical properties of nanocrystalline materials(1,2) is well known. However, elucidating this influence experimentally is difficult because grains typically exhibit a large range of sizes, shapes and random relative orientations(3-5). Here we demonstrate that precise control of the heteroepitaxy of colloidal polyhedral nanocrystals enables ordered grain growth and can thereby produce material samples with uniform GB defects. We illustrate our approach with a multigrain nanocrystal comprising a Co3O4 nanocube core that carries a Mn3O4 shell on each facet. The individual shells are symmetry-related interconnected grains(6), and the large geometric misfit between adjacent tetragonal Mn3O4 grains results in tilt boundaries at the sharp edges of the Co3O4 nanocube core that join via disclinations. We identify four design principles that govern the production of these highly ordered multigrain nanostructures. First, the shape of the substrate nanocrystal must guide the crystallographic orientation of the overgrowth phase(7). Second, the size of the substrate must be smaller than the characteristic distance between the dislocations. Third, the incompatible symmetry between the overgrowth phase and the substrate increases the geometric misfit strain between the grains. Fourth, for GB formation under near-equilibrium conditions, the surface energy of the shell needs to be balanced by the increasing elastic energy through ligand passivation(8-10). With these principles, we can produce a range of multigrain nanocrystals containing distinct GB defects.


  
Radar sounder evidence of thick, porous sediments in Meridiani Planum and implications for ice-filled deposits on Mars 期刊论文
GEOPHYSICAL RESEARCH LETTERS, 2017, 44 (18)
作者:  Watters, Thomas R.;  Leuschen, Carl J.;  Campbell, Bruce A.;  Morgan, Gareth A.;  Cicchetti, Andrea;  Grant, John A.;  Phillips, Roger J.;  Plaut, Jeffrey J.
收藏  |  浏览/下载:32/0  |  提交时间:2019/04/09
Mars  MARSIS  Meridiani Planum  electrical properties  compaction  water ice  
International Conference on Informatics, Technology and Engineering (InCITE) 2017 会议
Kuta, Indonesia, 会议类型: Conference, 2017