共查询到20条相似文献，搜索用时 31 毫秒
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石墨烯是一种仅由碳原子构成的二维材料.由于其独特的二维六角蜂窝状的晶格结构、载流子的狄拉克费米子行为及其他奇妙的物理特性,近些年来引起了人们的广泛关注.同时,它还展现出在电子、信息、能源等多个领域的巨大应用前景.曼彻斯特大学的安德烈.海姆（A.K.Geim）和康斯坦丁.诺沃肖洛夫（K.S.Novoselov）因其在石墨烯制备和研究方面的开创性工作获得了2010年的诺贝尔物理学奖. 相似文献
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超临界圆映象的混沌测度及其标度律 总被引：1，自引：0，他引：1
本文研究了圆映象中的参数k>1与k》1情况的混沌运动的行为,用在Ω轴的等分点上计算李雅普诺夫指数及转数的办法,给出混沌运动的测度及其标度律。关键词： 相似文献
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Kolmogorov的5／3次方律E（k）=Cε^2/3k^-5/3矿乃是20世纪湍流研究最重要的理论研究成果。这里E代表湍流能谱，占为湍流能量耗散率，k为波数，C为一常量。在极高雷诺数流动中-5／3次方律被很多实测数据验证。但是对于有限雷诺数问题，湍流能谱具有-5／3次方律的波数范围一般很窄；湍流实验证实，瞬时湍动能耗散存在时空分布极不均匀的情况，即所谓的间歇性现象，湍流物理量呈明显的非高斯分布， 相似文献
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在量热完全气体、热完全气体和化学反应完全气体等3种气体模型假设下,利用Mach数为4.05、壁温为1 300 K的超声速槽道湍流的直接数值模拟（direct numerical simulation,DNS）结果,对标度律和自相似性做了详细分析.结果表明,不仅在量热完全气体模型下存在标度律和扩展自相似性,而且在热完全气体和化学反应完全气体模型下标度律和扩展自相似性仍然成立.压缩性的影响使得速度结构函数通过Favre平均获得更为合适.与热完全气体模型的结果相比,化学反应完全气体和量热完全气体模型的结果吻合更好. 相似文献
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目前国际公认精度最高的现代电阻计量技术是量子霍尔电阻计量技术,但是其量子化、非连续特性使它在实际计量应用中受到很多限制。本文围绕先进的电阻比较与计量技术进行分类对比与分析,同时为实现10E-8量级相对不确定度的电阻溯源给出可行的技术方案。最后,针对不同方案给出分析结论,为相关计量实验室根据自身条件建立高精度电阻计量标准提供重要参考。 相似文献
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David Bailin 《Contemporary Physics》2013,54(3):292-293
An introduction to the theory of modular symmetries in two-dimensional materials, and its application to ‘relativistic’ group IV materials like graphene, silicene, germanene and stanene, is given. Universal properties of the magneto-electric Hall effect are extracted by projecting experimental transport data directly onto the phase diagram. When families of data depending on the dominant scale parameter (usually temperature) are available, we can extract flow lines that chart the geometry of the phase diagram, including the location of quantum critical points and phase boundaries connecting these. The universal data are used to identify emergent modular symmetries, which are infinite discrete groups of fractional linear (Möbius) transformations. Such symmetries are extremely rigid, and therefore spawn a host of sharp predictions that are easy to falsify, but so far they have failed to fail. The unique topology of the Fermi surface in the graphene family gives a robust gapless mode with linear dispersion (relativistic Dirac cones) that shifts the spectrum of Landau levels that appear when the material is placed in a strong magnetic field. The modular analysis can be extended to this case, and where reliable data are available, there appears to be agreement. A convincing case for the ‘relativistic’ quantum Hall group is hampered by the paucity of fractional quantum Hall data, the absence of scaling data and the crossover between different scaling regimes. This is likely to change in the near future, as scaling data for graphene are just now becoming available. 相似文献
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Ferdinand Kisslinger Dennis Rienmüller Christian Ott Erik Kampert Heiko B. Weber 《Annalen der Physik》2019,531(7)
A simple route to generate magnetotransport data is reported that results in fractional quantum Hall plateaus in the conductance without invoking strongly correlated physics. Ingredients to the generating model are conducting tiles with integer quantum Hall effect and metallic linkers, further Kirchhoff rules. When connecting few identical tiles in a mosaic, fractional steps occur in the conductance values. Richer spectra representing several fractions occur when the tiles are parametrically varied. Parts of the simulation data are supported with purposefully designed graphene mosaics in high magnetic fields. The findings emphasize that the occurrence of fractional conductance values, in particular in two‐terminal measurements, does not necessarily indicate interaction‐driven physics. The importance of an independent determination of charge densities is underscored and similarities with and differences to the fractional quantum Hall effect are critically discussed. 相似文献
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Xinzhou Deng Hualing Yang Shifei Qi Xiaohong Xu Zhenhua Qiao 《Frontiers of Physics》2018,13(5):137308
Quantum anomalous Hall effect (QAHE) is a fundamental quantum transport phenomenon in condensed matter physics. Until now, the QAHE has only been experimentally realized for Cr/V-doped (Bi, Sb)2Te3 but at an extremely low observational temperature, thereby limiting its potential application in dissipationless quantum electronics. By employing first-principles calculations, we study the electronic structures of graphene co-doped with 5d transition metal and boron atoms based on a compensated n–p co-doping scheme. Our findings are as follows: i) The electrostatic attraction between the n- and p-type dopants effectively enhances the adsorption of metal adatoms and suppresses their undesirable clustering. ii) Hf-B and Os-B co-doped graphene systems can establish long-range ferromagnetic order and open larger nontrivial band gaps because of the stronger spin-orbit coupling with the non-vanishing Berry curvatures to host the high-temperature QAHE. iii) The calculated Rashba splitting energies in Re–B and Pt–B co-doped graphene systems can reach up to 158 and 85 meV, respectively, which are several orders of magnitude higher than the reported intrinsic spin-orbit coupling strength. 相似文献
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Graphene has attracted enormous attention over the past years in condensed matter physics. The most interesting feature of graphene is that its low-energy excitations are relativistic Dirac fermions. Such feature is the origin of many topological properties in graphene-like physics. On the other hand, ultracold quantum gas trapped in an optical lattice has become a unique setting for quantum simulation of condensed matter physics. Here, we mainly review our recent work on quantum simulation of graphene-like physics with ultracold atoms trapped in a honeycomb or square optical lattice, including the simulation of Dirac fermions and quantum Hall effect with and without Landau levels. We also present the related experimental advances. 相似文献
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Y-shaped Kekulébond textures in a honeycomb lattice on a graphene-copper superlattice have recently been experimentally revealed.In this paper,the effects of such a bond modulation on the transport coefficients of Kekulé-patterned graphene are investigated in the presence of a perpendicular magnetic field.Analytical expressions are derived for the Hall and longitudinal conductivities using the Kubo formula.It is found that the Y-shaped Kekulébond texture lifts the valley degeneracy of all Landau levels except that of the zero mode,leading to additional plateaus in the Hall conductivity accompanied by a split of the corresponding peaks in the longitudinal conductivity.Consequently,the Hall conductivity is quantized as±ne2/h for n=2,4,6,8,10,...,excluding some plateaus that disappear due to the complete overlap of the Landau levels of different cones.These results also suggest that DC Hall conductivity measurements will allow us to determine the Kekulébond texture amplitude. 相似文献
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The present study pertains to the trilayer graphene in the presence of spin orbit coupling to probe the quantum spin/valley Hall effect. The spin Chern-number C_s for energy-bands of trilayer graphene having the essence of intrinsic spin–orbit coupling is analytically calculated. We find that for each valley and spin, C_s is three times larger in trilayer graphene as compared to single layer graphene. Since the spin Chern-number corresponds to the number of edge states,consequently the trilayer graphene has edge states, three times more in comparison to single layer graphene. We also study the trilayer graphene in the presence of both electric-field and intrinsic spin–orbit coupling and investigate that the trilayer graphene goes through a phase transition from a quantum spin Hall state to a quantum valley Hall state when the strength of the electric field exceeds the intrinsic spin coupling strength. The robustness of the associated topological bulk-state of the trilayer graphene is evaluated by adding various perturbations such as Rashba spin–orbit(RSO) interaction αR, and exchange-magnetization M. In addition, we consider a theoretical model, where only one of the outer layers in trilayer graphene has the essence of intrinsic spin–orbit coupling, while the other two layers have zero intrinsic spin–orbit coupling.Although the first Chern number is non-zero for individual valleys of trilayer graphene in this model, however, we find that the system cannot be regarded as a topological insulator because the system as a whole is not gaped. 相似文献
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J. S. Moon J. A. Simmons B. L. Johnson J. L. Reno 《Physica E: Low-dimensional Systems and Nanostructures》2000,6(1-4)
The propagation direction of fractional quantum Hall effect (FQHE) edge states has been investigated experimentally via the symmetry properties of the multi-terminal capacitances of a two-dimensional electron gas. Although strong asymmetries with respect to zero magnetic field appear, no asymmetries with respect to even denominator Landau level filling factor ν are seen. This indicates that current-carrying FQHE edge states propagate in the same direction as integer QHE edge states. In addition, anomalous capacitance features, indicative of enhanced bulk conduction, are observed at and . 相似文献
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Current breakdown of the integer and fractional quantum Hall effects detected by torque magnetometry
A. J. Matthews J. P. Watts M. Zhu A. Usher M. Elliott W. G. Herrenden-Harker P. R. Morris M. Y. Simmons D. A. Ritchie 《Physica E: Low-dimensional Systems and Nanostructures》2000,6(1-4)
We have developed a novel technique that enables measurements of the breakdown of both the integer and fractional quantum Hall effects in a two-dimensional electron system without the need to contact the sample. The critical Hall electric fields that we measure are significantly higher than those reported by other workers, and support the quasi-elastic inter-Landau-level tunnelling model of breakdown. Comparison of the fractional quantum Hall effect results with those obtained on the integer quantum Hall effect allows the fractional quantum Hall effect energy gap to be determined and provides a test of the composite-fermion theory. The temperature dependence of the critical current gives an insight into the mechanism by which momentum may be conserved during the breakdown process. 相似文献