Screening in Two-Dimensional Electron Liquid

Bulutay, Ceyhun; Gunalp, N.; Tomak, Mehmet

doi:10.1007/978-94-009-1778-1_39

Cited by 2 publications

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“…We thus arrive at the important conclusion that it is the electrons' spin that plays a crucial role. Indeed, among the theoretical suggestions that have been offered as possible explanations of the conducting phase at H = 0 [15,16,17,18,19,20,21], several involve electron spins [15,17,18,19].…”

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Effect of a tilted magnetic field on the anomalousH=0conducting phase in high-mobility Si MOSFET’s

et al. 1998

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The suppression by a magnetic field of the anomalous H = 0 conducting phase in high-mobility silicon MOSFETs is independent of the angle between the field and the plane of the 2D electron system. In the presence of a parallel field large enough to fully quench the anomalous conducting phase, the behavior is similar to that of disordered GaAs/AlGaAs heterostructures: the system is insulating in zero (perpendicular) field and exhibits reentrant insulator-quantum Hall effect-insulator transitions as a function of perpendicular field. The results demonstrate that the suppression of the low-T phase is related only to the electrons' spin.PACS numbers: 71.30.+h, 73.40.Qv, 73.40.Hm According to the one-parameter scaling theory of localization for non-interacting electrons [1], a twodimensional electron system (2DES) is always insulating at sufficiently large length scales (i.e., in the limit of zero temperature) in the absence of a magnetic field. In high-mobility silicon metal-oxide-semiconductor field-effect transistors (MOSFETs), however, a metalinsulator transition has been observed at a critical electron density, n c ∼ 10 11 cm −2 , and a H = 0 conducting phase has been shown to exist below 1 K [2]. Similar critical behavior has been reported in a p-type SiGe quantum well [3] and in the hole gas in GaAs/AlGaAs heterostructures [4,5]. At low carrier densities, the interaction energy in these systems is more than an order of magnitude larger than the Fermi energy, so that one does not expect the non-interacting theory of localization [1] to be applicable in its simplest form.In a disordered 2DES, Khmel'nitskii [6] predicted that the extended states that exist at the centers of each Landau level in large perpendicular magnetic fields should "float" up in energy as H ⊥ → 0, leading to an insulating phase at H = 0. Consistent with this expectation, insulating behavior has been observed in low-density, strongly disordered 2DES in GaAs/AlGaAs heterostructures [7,8]. In contrast, the low-density 2DES in highmobility Si MOSFETs exhibits quite different behavior. As H ⊥ → 0, the extended states shift upward from the centers of the Landau levels [9], as expected. However, instead of "floating" up indefinitely with decreasing magnetic field, the states apparently combine at the Fermi level [9,10], giving rise to anomalous field dependence of ρ xx in small magnetic fields first reported in Ref. [11] and shown in the inset to Fig. 1. This behavior is a puzzle, and its physical origin has remained unclear.We have recently shown that the anomalous lowdensity/low-temperature conducting phase in silicon MOSFETs is suppressed by a magnetic field applied parallel to the 2D plane of the electrons [12,13]: as shown in Fig. 2 in Ref. [12], the resistivity increases by several orders of magnitude as the parallel magnetic field is increased to H || ∼ 20 kOe, above which it saturates to a value that is approximately independent of magnetic field. This prompted us to suggest that the enigmatic behavior in small perpendicular fields is ass...

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Effect of a tilted magnetic field on the anomalousH=0conducting phase in high-mobility Si MOSFET’s

et al. 1998

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“…Another source of motivation for the present work is related to the recently observed Metal-Insulator transition in a 2D system, Si MOSFET, towards zero temperature. [20][21][22][23] We commented 24 that this observation could be due to valley phase transition in Si inversion layers, a many-body effect originally anticipated by Bloss, Sham and Vinter. 25 For this reason, the effect of valley degeneracy on several physical phenomena needs further investigation; the screening of charged impurity centers is just one of them.…”

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Effect of valley-spin degeneracy on the screening of charged-impurity centers in two- and three-dimensional electronic devices

1997

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Accurate characterization of charged impurity centers is of importance for the electronic devices and materials. The role of valley-spin degeneracy on the screening of an attractive ion by the mobile carriers is assessed within a range of systems from spin-polarized single-valley to six-valley. The screening is treated using the self-consistent local-field correction of Singwi and co-workers known as STLS. The bound electron wave function is formulated in the form of an integral equation. Friedel oscillations are seen to be influential especially in two-dimensions which cannot be adequately accounted for by the hydrogenic variational approaches. Our results show appreciable differences at certain densities with respect to simplified techniques, resulting mainly in the enhancement of the impurity binding energies. The calculated Mott constants are provided where available. The main conclusion of the paper is the substantial dependence of the charged impurity binding energy on the valley-spin degeneracy in the presence of screening. 73.20.Hb, 71.45.Gm

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Screening in Two-Dimensional Electron Liquid

Cited by 2 publications

References 3 publications

Effect of a tilted magnetic field on the anomalousH=0conducting phase in high-mobility Si MOSFET’s

Effect of a tilted magnetic field on the anomalousH=0conducting phase in high-mobility Si MOSFET’s

Effect of valley-spin degeneracy on the screening of charged-impurity centers in two- and three-dimensional electronic devices

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