Showing papers by "Chao Zhang published in 1990"
TL;DR: Cette theorie est fondee sur l'approximation auto-coherente de Born pour la diffusion par des impuretes de courtes distances distribuees aleatoirement, un nouveau type d'oscillation de periode B −1 dependant a la fois of the densite d'electrons and of the periodes de the modulation spatiale.
Abstract: A consistent theory of magnetotransport and collision broadening for a two-dimensional electron system with a periodic modulation in one direction is presented. The theory is based on the self-consistent Born approximation for the scattering by randomly distributed short-range impurities and explains recent experiments which revealed, in addition to the familiar Shubnikov--de Haas oscillations at stronger magnetic field, a new type of low-field oscillation, also periodic in ${\mathit{B}}^{\mathrm{\ensuremath{-}}1}$ but with a period depending on both the electron density and the period of the spatial modulation. It is shown that the antiphase oscillations observed for the resistivity components ${\mathrm{\ensuremath{\rho}}}_{\mathit{x}\mathit{x}}$ and ${\mathrm{\ensuremath{\rho}}}_{\mathit{y}\mathit{y}}$ have as a common origin the oscillating bandwidth of the modulation-broadened Landau bands, which reflects the commensurability of the period of the spatial modulation and the extent of the Landau wave functions. Recent magnetocapacitance experiments are also well understood within this theory.
108 citations
24 citations
TL;DR: In this paper, the authors calculate transport coefficients and collision broadening due to random impurity scattering within a self-consistent quantum mechanical damping theory, and obtain, in addition to the Shubnikov-de Haas oscillations, antiphase oscillations for different resistance components as a consequence of a unidirectional periodic modulation.
12 citations
TL;DR: In a recent Letter, Cui, Fessatidis, and Horing calculated the new intra-Landau-band magnetoplasma spectrum co for a periodically density-modulated twodimensional electron gas (2DEG), and it is pointed out that the spectrum presented is not correct.
Abstract: In a recent Letter, Cui, Fessatidis, and Horing calculated the new intra-Landau-band magnetoplasma spectrum co for a periodically density-modulated twodimensional electron gas (2DEG). Such low-energy plasmon excitation again exhibits the novel commensurability oscillations due to the modulation broadening of the Landau bands. The existence of this new plasmon mode and its period of oscillations have the same origin as in the magnetoresistance and magnetocapacitance of a modulated 2DEG. In this Comment, I would like to point out that the spectrum presented in Ref. 1 is not correct. According to their final result (also see Fig. 1 of Ref. 1) the frequency co vanishes with the modulation potential as |K„| and there are finite gaps between the Landau bands in co (all notations used here are adopted from Ref. 1). The former is correct within the perturbation scheme but the latter is qualitatively wrong. The gaps appearing in co are not physically meaningful. If one treats the Fermi energy self-consistently, the spectrum should be gapless regardless of how small the modulation potential is. This can be illustrated as follows. From Ref. 1, the intra-Landau-band mode is given as co — Z j K „ | ( l A „ ) 1 / 2 0 ( 1 A „ ) . For 2\\Vn\\ > coc, it is clear that co is nonzero everywhere. I can also show that even for 2\\Vn\\<£coc, co only contains discrete zeros but has no finite gaps. In the absence of other scatterers, the density of states can be written as
7 citations
TL;DR: In this article, the hopping rate of localized defects interacting with a two-dimensional electron system is studied, and it is shown that, at low temperatures, hopping rate is an oscillatory function of the inverse of the magnetic field.
3 citations
TL;DR: In this article, longitudinal field muon spin relaxation was used to probe the local charge density correlations in two-dimensional systems and heterostructures, and magnetic quantum oscillations in the local density of extended states showed up in the relaxation time T1.
Abstract: It is shown that longitudinal field muon spin relaxation may be used to probe the local charge density correlations in two-dimensional systems and heterostructures. Magnetic quantum oscillations in the local density of extended states show up in the relaxation time T1. This method should reveal the variation of electronic parameters within the sample.