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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.


  
Operation of a silicon quantum processor unit cell above one kelvin 期刊论文
NATURE, 2020, 580 (7803) : 350-+
作者:  Han, Kyuho;  Pierce, Sarah E.;  Li, Amy;  Spees, Kaitlyn;  Anderson, Grace R.;  Seoane, Jose A.;  Lo, Yuan-Hung;  Dubreuil, Michael;  Olivas, Micah;  Kamber, Roarke A.;  Wainberg, Michael;  Kostyrko, Kaja;  Kelly, Marcus R.;  Yousefi, Maryam;  Simpkins, Scott W.;  Yao, David
收藏  |  浏览/下载:32/0  |  提交时间:2020/07/03

Quantum computers are expected to outperform conventional computers in several important applications, from molecular simulation to search algorithms, once they can be scaled up to large numbers-typically millions-of quantum bits (qubits)(1-3). For most solid-state qubit technologies-for example, those using superconducting circuits or semiconductor spins-scaling poses a considerable challenge because every additional qubit increases the heat generated, whereas the cooling power of dilution refrigerators is severely limited at their operating temperature (less than 100 millikelvin)(4-6). Here we demonstrate the operation of a scalable silicon quantum processor unit cell comprising two qubits confined to quantum dots at about 1.5 kelvin. We achieve this by isolating the quantum dots from the electron reservoir, and then initializing and reading the qubits solely via tunnelling of electrons between the two quantum dots(7-9). We coherently control the qubits using electrically driven spin resonance(10,11) in isotopically enriched silicon(12 28)Si, attaining single-qubit gate fidelities of 98.6 per cent and a coherence time of 2 microseconds during '  hot'  operation, comparable to those of spin qubits in natural silicon at millikelvin temperatures(13-16). Furthermore, we show that the unit cell can be operated at magnetic fields as low as 0.1 tesla, corresponding to a qubit control frequency of 3.5 gigahertz, where the qubit energy is well below the thermal energy. The unit cell constitutes the core building block of a full-scale silicon quantum computer and satisfies layout constraints required by error-correction architectures(8),(17). Our work indicates that a spin-based quantum computer could be operated at increased temperatures in a simple pumped He-4 system (which provides cooling power orders of magnitude higher than that of dilution refrigerators), thus potentially enabling the integration of classical control electronics with the qubit array(18,19).


  
Observation of the Kondo screening cloud 期刊论文
NATURE, 2020, 579 (7798) : 210-+
作者:  Shahnawaz, Mohammad;  Mukherjee, Abhisek;  Pritzkow, Sandra;  Mendez, Nicolas;  Rabadia, Prakruti;  Liu, Xiangan;  Hu, Bo;  Schmeichel, Ann;  Singer, Wolfgang;  Wu, Gang;  Tsai, Ah-Lim;  Shirani, Hamid;  Nilsson, K. Peter R.;  Low, Phillip A.;  Soto, Claudio
收藏  |  浏览/下载:24/0  |  提交时间:2020/07/03

When a magnetic impurity exists in a metal, conduction electrons form a spin cloud that screens the impurity spin. This basic phenomenon is called the Kondo effect(1,2). Unlike electric-charge screening, the spin-screening cloud(3-6) occurs quantum coherently, forming spin-singlet entanglement with the impurity. Although the spins interact locally around the impurity, the Kondo cloud can theoretically spread out over several micrometres. The cloud has not so far been detected, and so its physical existence-a fundamental aspect of the Kondo effect-remains controversial(7,8). Here we present experimental evidence of a Kondo cloud extending over a length of micrometres, comparable to the theoretical length xi(K). In our device, a Kondo impurity is formed in a quantum dot(2,9-11), coupling on one side to a quasi-one-dimensional channel(12) that houses a Fabry-Perot interferometer of various gate-defined lengths L exceeding one micrometre. When we sweep a voltage on the interferometer end gate-separated by L from the quantum dot-to induce Fabry-Perot oscillations in conductance we observe oscillations in the measured Kondo temperature T-K, which is a signature of the Kondo cloud at distance L. When L is less than xi(K) the T-K oscillation amplitude becomes larger as L becomes smaller, obeying a scaling function of a single parameter L/xi(K), whereas when L is greater than xi(K) the oscillation is much weaker. Our results reveal that xi(K) is the only length parameter associated with the Kondo effect, and that the cloud lies mostly within a length of xi(K). Our experimental method offers a way of detecting the spatial distribution of exotic non-Fermi liquids formed by multiple magnetic impurities or multiple screening channels(13-16) and of studying spin-correlated systems.


  
The relationship of atmospheric air temperature and dew point temperature to extreme rainfall 期刊论文
ENVIRONMENTAL RESEARCH LETTERS, 2019, 14 (7)
作者:  Bui, Andrew;  Johnson, Fiona;  Wasko, Conrad
收藏  |  浏览/下载:20/0  |  提交时间:2019/11/27
precipitation  atmospheric temperature  atmospheric dew point  scaling  Clausius-Clapeyron  climate change  
Size-based ecological interactions drive food web responses to climate warming 期刊论文
ECOLOGY LETTERS, 2019, 22 (5) : 778-786
作者:  Lindmark, Max;  Ohlberger, Jan;  Huss, Magnus;  Gardmark, Anna
收藏  |  浏览/下载:22/0  |  提交时间:2019/11/26
Allee effects  alternative stable states  climate change  community dynamics  size structure  temperature-scaling  trophic interactions  
Global Observational Evidence of Strong Linkage Between Dew Point Temperature and Precipitation Extremes 期刊论文
GEOPHYSICAL RESEARCH LETTERS, 2018, 45 (22) : 12320-12330
作者:  Ali, Haider;  Fowler, Hayley J.;  Mishra, Vimal
收藏  |  浏览/下载:16/0  |  提交时间:2019/04/09
extreme precipitation  air temperature  dew point temperature  scaling  binning  quantile regression  
Reply to comments on "Temperature-extreme precipitation scaling: a two-way causality?" 期刊论文
INTERNATIONAL JOURNAL OF CLIMATOLOGY, 2018, 38 (12) : 4664-4666
作者:  Lenderink, Geert;  Barbero, Renaud;  Westra, Seth;  Fowler, Hayley J.
收藏  |  浏览/下载:30/0  |  提交时间:2019/04/09
Australia  climate change  dew point temperature  precipitation extreme  temperature-extreme precipitation scaling  
Comments on "temperature-extreme precipitation scaling: A two-way causality?" 期刊论文
INTERNATIONAL JOURNAL OF CLIMATOLOGY, 2018, 38 (12) : 4661-4663
作者:  Bao, Jiawei;  Sherwood, Steven C.;  Alexander, Lisa V.;  Evans, Jason P.
收藏  |  浏览/下载:15/0  |  提交时间:2019/04/09
climate change  dew point temperature  extreme precipitation  extreme precipitation scaling  
Relationship of extreme precipitation, dry-bulb temperature, and dew point temperature across Australia 期刊论文
ENVIRONMENTAL RESEARCH LETTERS, 2018, 13 (7)
作者:  Wasko, Conrad;  Lu, William Tang;  Mehrotra, Rajeshwar
收藏  |  浏览/下载:17/0  |  提交时间:2019/04/09
precipitation  temperature  dew point  scaling  Clausius-Clapeyron  climate change  
Temperature-extreme precipitation scaling: a two-way causality? 期刊论文
INTERNATIONAL JOURNAL OF CLIMATOLOGY, 2018, 38: E1274-E1279
作者:  Barbero, R.;  Westra, S.;  Lenderink, G.;  Fowler, H. J.
收藏  |  浏览/下载:14/0  |  提交时间:2019/04/09
precipitation extreme  temperature-extreme precipitation scaling  dew point temperature  Australia  climate change