共查询到20条相似文献,搜索用时 15 毫秒
1.
The transition from partial to complete spin polarization of two-dimensional electrons at half filling of the lowest Landau level has been studied using resistively detected nuclear magnetic resonance (RDNMR). The nuclear spin-lattice relaxation time is observed to be density independent in the partially polarized phase but to increase sharply at the transition to full polarization. At low temperatures the RDNMR signal exhibits a strong maximum near the critical density. 相似文献
2.
C. -T. Liang J. E. F. Frost M. Y. Simmons D. A. Ritchie M. Pepper 《Physica E: Low-dimensional Systems and Nanostructures》1998,2(1-4)
We have measured the low-temperature transport properties of a high-mobility front-gated GaAs/Al
Ga
As heterostructure. By changing the applied gate voltage, we can vary the amount of disorder within the system. At a Landau level filling factor
, where the system can be described by the composite fermion picture, we observe a crossover from metallic to insulating behaviour as the disorder is increased, in agreement with theory. We also report experimental evidence of geometric effect for composite fermions induced by an effective magnetic field. 相似文献
3.
Abstract Existing experimental data for the antiferroelastic phase transition in strontium titanate are reviewed and analysed using a Landau free energy of the form ΔG = 1/2Aθs (cothθs/ Tc-colb.θ/T)Q2 + 1/4BQ 4 + 1/6CQ 6, with A = 0·6472 J K?1mol?1, B = 29·12 Jmol?1, C = 39·27 Jmol, T c= 105·6 K, θ S = 60·8 K. The temperature dependence of the critical exponent is found to be due to the delicate balance between the Q 4 and Q 6 terms in the free energy expansion, and the saturation of the order parameter at low temperatures. The spontaneous strains observed in this phase transition are not consistent with simple rotation of the TiO6 octahedra around [001], An alternative model is proposed, where these octahedra expand in order to preserve the volume of the twelve-fold co-ordinated Sr site and the spacing between SrO3 pseudo-closepacked layers. 相似文献
4.
5.
Csáthy GA Xia JS Vicente CL Adams ED Sullivan NS Stormer HL Tsui DC Pfeiffer LN West KW 《Physical review letters》2005,94(14):146801
We have investigated the behavior of electronic phases of the second Landau level under tilted magnetic fields. The fractional quantum Hall liquids at nu=2+1/5 and 2+4/5 and the solid phases at nu=2.30, 2.44, 2.57, and 2.70 are quickly destroyed with tilt. This behavior can be interpreted as a tilt driven localization of the 2+1/5 and 2+4/5 fractional quantum Hall liquids and a delocalization through the melting of solid phases in the top Landau level, respectively. The evolution towards the classical Hall gas of the solid phases is suggestive of antiferromagnetic ordering. 相似文献
6.
In this paper we will discuss the conditions under which the
free-electron laser interaction in a storage ring may reinforce
the effect of the Landau damping, thus leading to the suppression
of different types of instabilities. The problem will be discussed
both by making use of general arguments and referring to the
specific examples. 相似文献
7.
The lowest Landau level of graphene is studied numerically by considering a tight-binding Hamiltonian with disorder. The Hall conductance sigma_{xy} and the longitudinal conductance sigma_{xx} are computed. We demonstrate that bond disorder can produce a plateaulike feature centered at nu=0, while the longitudinal conductance is nonzero in the same region, reflecting a band of extended states between +/-E_{c}, whose magnitude depends on the disorder strength. The critical exponent corresponding to the localization length at the edges of this band is found to be 2.47+/-0.04. When both bond disorder and a finite mass term exist the localization length exponent varies continuously between approximately 1.0 and approximately 7/3. 相似文献
8.
近年来, 硅烯(单层硅)由于其独特的结构和电子性质以及在量子霍尔效应等领域的潜在应用而成为理论和实验研究的一个热点. 借助于四带次近邻紧束缚模型, 详细计算和研究了硅烯中受电场调制的体能隙和电子能级. 结果表明: 硅烯原胞中的两个子格处于不同的平面上, 可以通过外电场区分和控制这两个子格, 这将破坏在纯石墨烯中无法被破坏的K-K'对称性, 并消除由这一对称性导致的电子能级的二重简并; 外加电场还会引起硅烯中次近邻格点之间的Rashba自旋轨道耦合, 这一作用会在不同狄拉克点有选择地消除电子能级在部分电场点的简并, 相邻能级从交叉状态变为反交叉状态; 电子能级中除一些孤立的交叉点外, 每个能级都具有确定的自旋取向, 石墨烯中电子能级的四重简并在硅烯中被完全消除, 从而导致填充因子ν=0, ±1, ±2, ±3,…的量子霍尔平台. 相似文献
9.
10.
Schweikhard V Coddington I Engels P Mogendorff VP Cornell EA 《Physical review letters》2004,92(4):040404
We create rapidly rotating Bose-Einstein condensates in the lowest Landau level by spinning up the condensates to rotation rates Omega > 99% of the centrifugal limit for a harmonically trapped gas, while reducing the number of atoms. As a consequence, the chemical potential drops below the cyclotron energy 2 variant Planck's over 2pi Omega. While in this mean-field quantum-Hall regime we still observe an ordered vortex lattice, its elastic shear strength is strongly reduced, as evidenced by the observed very low frequency of Tkachenko modes. Furthermore, the gas approaches the quasi-two-dimensional limit. The associated crossover from interacting- to ideal-gas behavior along the rotation axis results in a shift of the axial breathing mode frequency. 相似文献
11.
We investigate the influence of a cosmological constant on the energy levels of a one-electron atom in Fermi normal coordinates.
The non-relativistic nS, nP energy levels and the relativistic 1S
1/2, 2S
1/2, 2P
1/2, 2P
3/2 energy levels are calculated in terms of the Riemann tensor. These energy level shifts are non-zero which indicate that the
first order gravitational perturbations can partly remove the degeneracy of the studied states in de Sitter space. We show
that it is not possible to use the hydrogen atom as a probe of background curvature of the universe. In the second order of
perturbation, for 1S state, an upper limit for the energy shifts is obtained. 相似文献
12.
The observation of new insulating phases of two-dimensional electrons in the first excited Landau level is reported. These states, which are manifested as reentrant integer quantized Hall effects, exist alongside well-developed even-denominator fractional quantized Hall states at nu = 7/2 and 5/2 and new odd-denominator states at nu = 3+1/5 and 3+4/5. 相似文献
13.
Laminar-turbulent transition in circular Couette flow is discussed. Phenomenological equations are proposed describing the breakdown of azimuthal waves coherency. The correspondence is established between the flow turbulization and the stochastic attractor in the phase space of these equations. Evolution of attractor structure is investigated experimentally in terms of motion in some effective phase space. It is shown that during the transition to turbulence the increase in number of degrees of freedom is combined with the stochastic behaviour of rapid motion envelopes. 相似文献
14.
《Current Applied Physics》2009,9(1):234-237
Sputtered deposited thin films of AlN:Pr and GaN:Pr emit in ultraviolet–visible and visible regions of the spectrum, respectively, under electron excitation in cathodoluminescence apparatus. The goal is to study the ultraviolet emission from Pr+3 when doped in nitride semiconductor hosts. Luminescence peaks at a wavelength of 295 nm (4.2 eV), 335 nm (3.7 eV) and 385 nm (3.24 eV) are observed as a result from 1S0 → 1G4, 1S0 → 1D2 and 1S0 → 1I6 transitions, respectively. However the 1S0 → 1G4 and 1S0 → 1D2 transitions are not observed when Pr+3 is doped in GaN host. The bandgap of GaN absorbs the ultraviolet radiation emitted from Pr+3 and hence GaN can be used as ultraviolet filter for radiation shielding and protection purposes. AlN is transparent to ultraviolet due to its wide bandgap of 6.2 eV. 相似文献
15.
Y. Kopelevich V. V. Lemanov S. Moehlecke J. H. S. Torres 《Physics of the Solid State》1999,41(12):1959-1962
Measurements of the basal-plane resistivity ρ
a(T,H) performed on highly oriented pyrolitic graphite, with magnetic field H∥c-axis in the temperature interval 2–300K and fields up to 8 T, provide evidence for the occurrence of both field-induced and
zero-field superconducting instabilities. Additionally, magnetization M(T,H) measurements suggest the occurrence of Fermi surface instabilities which compete with the superconducting correlations.
Fiz. Tverd. Tela (St. Petersburg) 41, 2135–2138 (December 1999) 相似文献
16.
Thirty one new cw far-infrared laser lines have been discovered in COF2 optically pumped by a CO2 laser and a N2O laser, in a metallic waveguide resonator. This number appreciably increases the number of eighteen lines appearing in the literature. Moreover, some of the new lines show that intense far-infrared laser action might be obtained with an optimized cavity, as it was the case for some of the previously reported lines. Twenty-seven, amongst the thirty one new lines, have been fully identified. 相似文献
17.
18.
S. R. Rotman 《Applied physics. B, Lasers and optics》1989,49(1):59-64
We apply a recently developed model for non-radiative energy transfer in correlated systems to recently published data on energy transfer in garnets. We show that even in well-studied materials in which the analysis of the data appears straightforward, subtle deviations from theory and difficulty in quantitatively evaluating interaction parameters may be due to a non-random distribution of donors and acceptors in the crystal. 相似文献
19.
20.
在超冷费米系统中实现人造规范势的突破,吸引了许多新问题的研究,展现了许多新奇的物理现象.本文研究了在环阱中,具有自旋轨道耦合和塞曼作用的两体相互作用费米模型.通过平面波展开的方法,解析求解了两体费米系统的本征能态.系统的总动量为守恒量,可以在不同总动量空间中研究能谱.研究发现:随着塞曼相互作用增大,在不同总动量空间,两体费米系统的本征能量均逐渐降低,系统基态从总动量为零空间转变到有限值空间.从吸引到排斥相互作用,无塞曼相互作用时,基态总动量始终为零,有塞曼相互作用时,基态总动量从零转变为有限值.通过单粒子和基态动量分布研究,本文直观地揭示了由塞曼能级劈裂引起的基态转变. 相似文献