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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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We present a systematic study of the corrections to both the longitudinal conductivity and Hall resistivity due to electron-electron interactions in high quality GaAs systems using the recent theory of Zala et al. [Phys. Rev. B 64, 214204 (2001)]. We demonstrate that the interaction corrections to the longitudinal conductivity and Hall resistivity predicted by the theory are consistent with each other. This suggests that the anomalous metallic drop in resistivity at B=0 is due to interaction effects and supports the theory of Zala et al.

This paper presents a short review of localisation in strongly interacting, high quality dilute 2D GaAs systems. At zero magnetic field, studies of the temperature dependent resistance of both 2D electron and hole systems show a transition from insulating to metallic behaviour with increasing carrier density. However, careful examination of the 2D hole systems reveal the presence of localising quantum corrections to the conductivity which persist down to the lowest measurement temperatures. Our results highlight the importance of avoiding electron/hole heating at low temperatures and argue against the existence of a 2D metallic phase at B ¼ 0.The scaling theory of localisation [1] predicts that there is no metallic phase in noninteracting two-dimensional (2D) systems at zero magnetic field and therefore that there can be no metal-insulator transition at T ¼ 0. Early experiments on weak localisation and interaction effects in 2D systems provided strong support for this theory, revealing a logarithmic increase in the low temperature resistance as T ! 0 [2, 3]. However, recent experimental studies of a wide variety of 2D semiconductor systems have demonstrated an unexpectedly large decrease in the resistance as the temperature is reduced below T $ 1 K, suggesting the possible existence of a 2D metal (see Ref.[4] for a recent review).In this paper, we present results from both high quality 2D GaAs electron and hole systems which exhibit this anomalous metallic-like behaviour at low temperatures. In the p-GaAs systems we use temperature dependent magneto-resistivity measurements to show that even in the metallic regime, both weak localisation and localising interaction corrections to the Drude conductivity are still present and increase logarithmically as T ! 0. The importance of sample heating is discussed. For the ultra-high quality electron systems it is extremely difficult to observe quantum corrections at experimentally accessible temperatures due to the long mean free path. In a separate work [5] we have used an alternative technique to ascertain the ultimate ground state of the n-GaAs system at T ¼ 0. Results from both n-and p-type GaAs argue against the existence of a 2D metallic phase at B ¼ 0.The samples used in this study have been described in detail elsewhere [5][6][7][8]. Sample A is an electron device fabricated from an undoped GaAs/AlGaAs heterostructure where the carriers are induced with a gate [5], whereas samples B and C are p-type 2D GaAs hole devices fabricated from modulation doped heterostructures [7,8]. The peak phys. stat. sol. (b) 230,