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Enhanced ferroelectricity in ultrathin films grown directly on silicon 期刊论文
NATURE, 2020, 580 (7804) : 478-+
作者:  Arnold, Fabian M.;  Weber, Miriam S.;  Gonda, Imre;  Gallenito, Marc J.;  Adenau, Sophia;  Egloff, Pascal;  Zimmermann, Iwan;  Hutter, Cedric A. J.;  Huerlimann, Lea M.;  Peters, Eike E.;  Piel, Joern;  Meloni, Gabriele;  Medalia, Ohad;  Seeger, Markus A.
收藏  |  浏览/下载:64/0  |  提交时间:2020/07/03

Ultrathin ferroelectric materials could potentially enable low-power perovskite ferroelectric tetragonality logic and nonvolatile memories(1,2). As ferroelectric materials are made thinner, however, the ferroelectricity is usually suppressed. Size effects in ferroelectrics have been thoroughly investigated in perovskite oxides-the archetypal ferroelectric system(3). Perovskites, however, have so far proved unsuitable for thickness scaling and integration with modern semiconductor processes(4). Here we report ferroelectricity in ultrathin doped hafnium oxide (HfO2), a fluorite-structure oxide grown by atomic layer deposition on silicon. We demonstrate the persistence of inversion symmetry breaking and spontaneous, switchable polarization down to a thickness of one nanometre. Our results indicate not only the absence of a ferroelectric critical thickness but also enhanced polar distortions as film thickness is reduced, unlike in perovskite ferroelectrics. This approach to enhancing ferroelectricity in ultrathin layers could provide a route towards polarization-driven memories and ferroelectric-based advanced transistors. This work shifts the search for the fundamental limits of ferroelectricity to simpler transition-metal oxide systems-that is, from perovskite-derived complex oxides to fluorite-structure binary oxides-in which '  reverse'  size effects counterintuitively stabilize polar symmetry in the ultrathin regime.


Enhanced switchable ferroelectric polarization is achieved in doped hafnium oxide films grown directly onto silicon using low-temperature atomic layer deposition, even at thicknesses of just one nanometre.


  
Submicrosecond entangling gate between trapped ions via Rydberg interaction 期刊论文
NATURE, 2020, 580 (7803) : 345-+
作者:  Chatterjee, Sourav;  Guidi, Mara;  Seeberger, Peter H.;  Gilmore, Kerry
收藏  |  浏览/下载:33/0  |  提交时间:2020/07/03

Generating quantum entanglement in large systems on timescales much shorter than the coherence time is key to powerful quantum simulation and computation. Trapped ions are among the most accurately controlled and best isolated quantum systems(1) with low-error entanglement gates operated within tens of microseconds using the vibrational motion of few-ion crystals(2,3). To exceed the level of complexity tractable by classical computers the main challenge is to realize fast entanglement operations in crystals made up of many ions (large ion crystals)(4). The strong dipole-dipole interactions in polar molecule(5) and Rydberg atom(6,7) systems allow much faster entangling gates, yet stable state-independent confinement comparable with trapped ions needs to be demonstrated in these systems(8). Here we combine the benefits of these approaches: we report a two-ion entangling gate with 700-nanosecond gate time that uses the strong dipolar interaction between trapped Rydberg ions, which we use to produce a Bell state with 78 per cent fidelity. The sources of gate error are identified and a total error of less than 0.2 per cent is predicted for experimentally achievable parameters. Furthermore, we predict that residual coupling to motional modes contributes an approximate gate error of 10(-4) in a large ion crystal of 100 ions. This provides a way to speed up and scale up trapped-ion quantum computers and simulators substantially.


  
Low-Level and Surface Wind Jets Near Sea Ice Edge in the Beaufort Sea in Late Autumn 期刊论文
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 2019, 124 (13) : 6873-6891
作者:  Liu, Zheng;  Schweiger, Axel
收藏  |  浏览/下载:11/0  |  提交时间:2019/11/27
low-level jet  sea ice edge  surface ice edge jet  polar meteorology  
In Situ Measurements of Surface Winds, Waves, and Sea State in Polar Lows Over the North Atlantic 期刊论文
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 2019, 124 (2) : 700-718
作者:  Rojo, M.;  Claud, C.;  Noer, G.;  Carleton, A. M.
收藏  |  浏览/下载:8/0  |  提交时间:2019/04/09
polar low  mesocyclone track  Norwegian Sea  North Sea  multiple system  in-situ measurement  
A stochastic model with a low-frequency amplification feedback for the stratospheric northern annular mode 期刊论文
CLIMATE DYNAMICS, 2018, 50: 3757-3773
作者:  Yu, Yueyue;  Cai, Ming;  Ren, Rongcai
收藏  |  浏览/下载:21/0  |  提交时间:2019/04/09
Stratospheric NAM variability  Polar stratospheric mass  Poleward mass transport  Linear stochastic model with a low-frequency amplification feedback