Coexistence of weak localization and a metallic phase in Si/SiGe quantum wells

Senz, Volkmar; Heinzel, T.; Ihn, Thomas; Ensslin, Klaus; Dehlinger, G.; Grützmacher, D.; Gennser, U.

doi:10.1103/physrevb.61.r5082

Cited by 46 publications

(46 citation statements)

References 57 publications

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“…But due to the lack of the "metallic" state in these low-mobility samples, no appropriate conclusion could be drawn. In recent studies on high-mobility samples with "metallic" behavior, it was shown that the WL has only small effects on ρ for GaAs/AlGaAs [6] and Si/SiGe [7]. Also for Si-MOS structures in the low ρ (high n) regime, the WL contribution is small and it was shown that spinorbit coupling is not visible for τ ϕ up to 100 ps [8].…”

mentioning

confidence: 99%

Exclusion of Quantum Coherence as the Origin of the 2D Metallic State in High-Mobility Silicon Inversion Layers

et al. 2001

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The temperature and density dependence of the phase coherence time τϕ in high-mobility silicon inversion layers was determined from the magnetoresistivity due to weak localization. The upper temperature limit for single-electron quantum interference effects was delineated by comparing τϕ with the momentum relaxation time τ . A comparison between the density dependence of the borders for quantum interference effects and the strong resistivity drop reveals that theses effects are not related to each other. As the strong resistivity drop occurs in the Drude regime, the apparent metallic behavior can not be caused by quantum coherent effects.The apparent "metallic" state in two dimensions (2D)[1] has attracted much attention as it seems to contradict the one parameter scaling theory of Abrahams et al. [2]. Following the confirmation of the "metallic" behavior in several material systems, the question was raised whether the "metallic" state constitutes a new quantum mechanical ground state, or if the resistivity drop towards lower temperature is based on semiclassical (i.e., noncoherent) effects (see [3] and references therein).We answer this question for Si-metal oxide semiconductor (MOS) structures, by excluding quantum interference (QI) effects as the origin of the "metallic" state. This is achieved by determining the phase coherence time τ ϕ from the weak localization (WL) behavior and comparing it with the momentum relaxation time τ at different temperatures T and densities n. For τ ϕ > τ (low-T regime), single-electron quantum interference effects occur, whereas for τ ϕ < τ (high-T ) they do not, as the coherence time is too short to allow electrons a coherent return to their origin. By comparing the phase coherent regime with the "metallic" regime, we find that they are not correlated with each other and that "metallic" behavior exists even without phase coherence. In addition, we dertermine the temperature where k B T =h/τ , which marks the threshold for coherent electron-electron (e − e) interaction effects. Again, no correlation with the "metallic" regime is found.The T dependence of the phase coherence was already investigated in the early 80's in Si-MOS structures (see [4,5]). But due to the lack of the "metallic" state in these low-mobility samples, no appropriate conclusion could be drawn. In recent studies on high-mobility samples with "metallic" behavior, it was shown that the WL has only small effects on ρ for GaAs/AlGaAs [6] and Si/SiGe [7]. Also for Si-MOS structures in the low ρ (high n) regime, the WL contribution is small and it was shown that spinorbit coupling is not visible for τ ϕ up to 100 ps [8]. But so far, the borders for phase coherence were not determined systematically on a sample with strong "metallic" behavior in order to decide among the possible underlying mechanisms.Our investigations were performed on two highmobility Si-MOS samples Si-15 and Si-43 with peak mobilities of µ = 31 000 and 20 000 cm 2 /Vs, respectively. Resistivity and Hall measurements were performed with a four t...

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confidence: 99%

Exclusion of Quantum Coherence as the Origin of the 2D Metallic State in High-Mobility Silicon Inversion Layers

et al. 2001

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“…(iii) Some experiments have been successfully interpreted in the framework of normal Fermi-liquid behavior of charge carriers on the metallic side of the transition (using the Hartree-Fock approximation), including weak-localization corrections [100,102,103]. In [102], magnetoresistance measurements were used to extract the logarithmic corrections to the Drude conductivity in the 'metallic' phase of a high-quality two-dimensional GaAs hole system at low temperatures.…”

Section: Evidence Against a True Metal-insulator Transition In Two-dimentioning

confidence: 99%

Charge Transport via Delocalized States in Disordered Materials

Zvyagin

2006

Charge Transport in Disordered Solids With Applications in Electronics

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“…10,13 Both studies find values of three to five times smaller than those predicted from Fermi-liquid theory. Phase breaking rates −1 have also been extracted and compared to theoretical values in other material systems, for example, p-SiGe, 9,15 and Si. 12 In all these cases where the method of Hikami was used to fit the data, the value of extracted was found to differ by the factor of 3-5 from the theoretical value.…”

Section: B Analysis Of the Phase Breaking Rate In P-gaasmentioning

confidence: 99%

“…Analysis of this positive magnetoconductivity has been widely used to measure the phase-coherence time and probe the dephasing mechanisms in 2D systems. [5][6][7][8][9][10][11][12][13][14][15] In order to reliably extract from the measured data it is essential to have an accurate method for determining the effect of the weak localization on the magnetoconductivity. While a good physical understanding of the weak localization effect exists, the numerical process by which experimental data are analyzed is not so well understood.…”

Section: Introductionmentioning

confidence: 99%

“…This factor of approximately 3 between the value of extracted using the Hikami method and the Fermi-liquid prediction has been repeatedly observed in experimental measurements of the phase breaking rate −1 on a variety of material systems. 8,9,[12][13][14][15] Our analysis of the B dependence of ⌬ wl allows us to explain the discrepancy.…”

Section: Introductionmentioning

confidence: 99%

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Weak localization in high-quality two-dimensional systems

et al. 2004

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We investigate five different methods of modeling the correction to the magnetoconductivity due to the weak localization effect in two-dimensional (2D) systems. The phase breaking rate is extracted using each method by fitting experimental magnetoconductivity data of high-quality 2D GaAs hole systems over the range of carrier densities and temperatures that weak localization is observed. We find that despite corrections to the magnetoconductivity differing by more than 100% between different methods valid beyond the diffusion approximation, the phase breaking rate extracted is approximately the same. We also find that if diffusive transport is incorrectly assumed in high-quality systems, then values of the phase breaking rate approximately 2.5 times too high are extracted. We demonstrate the regime in which the diffusive transport approximation holds and explain previous discrepancies in the literature where phase breaking rates much higher than expected from Fermi-liquid theory have been obtained. We find good agreement of the phase breaking rate with Fermi-liquid theory until k F l begins to approach 1.

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Coexistence of weak localization and a metallic phase in Si/SiGe quantum wells

Cited by 46 publications

References 57 publications

Exclusion of Quantum Coherence as the Origin of the 2D Metallic State in High-Mobility Silicon Inversion Layers

Exclusion of Quantum Coherence as the Origin of the 2D Metallic State in High-Mobility Silicon Inversion Layers

Charge Transport via Delocalized States in Disordered Materials

Weak localization in high-quality two-dimensional systems

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