Comment on "Theory of metal-insulator transitions in gated semiconductors" (B. L. Altshuler and D. L. Maslov, Phys. Rev. Lett. 82, 145 (1999))

In a recent Letter, Altshuler and Maslov propose a model which attributes the anomalous temperature and field dependence of the resistivity of two-dimensional electron (or hole) systems to the charging and discharging of traps in the oxide (spacer), rather than to intrinsic behavior of interacting particles associated with a conductor-insulator transition in two dimensions. We argue against this model based on existing experimental evidence.Comment: 1 page; submitted to PR

Deconstruction of the Trap Model for the New Conducting State in 2D

A key prediction of the trap model for the new conducting state in 2D is that the resistivity turns upwards below some characteristic temperature, $T_{\rm min}$. Altshuler, Maslov, and Pudalov have argued that the reason why no upturn has been observed for the low density conducting samples is that the temperature was not low enough in the experiments. We show here that $T_{\rm min}$ within the Altshuler, Maslov, and Pudalov trap model actually increases with decreasing density, contrary to their claim. Consequently, the trap model is not consistent with the experimental trends.Comment: Published version of Deconstructio

Novel Properties of The Apparent Metal-Insulator Transition in Two-Dimensional Systems

The low-temperature conductivity of low-density, high-mobility, two-dimensional hole systems in GaAs was studied. We explicitly show that the metal-insulator transition, observed in these systems, is characterized by a well-defined critical density, p_0c. We also observe that the low-temperature conductivity of these systems depends linearly on the hole density, over a wide density range. The high-density linear conductivity extrapolates to zero at a density close to the critical density.Comment: 4 Figure

Observation of the Metal-Insulator Transition in Two-Dimensional n-type GaAs

The observation of a carrier-density driven metal-insulator transition in n-type GaAs-based heterostructure is reported. Although weaker than in comparable-quality p-type GaAs samples, the main features of the transition are rather similar.Comment: 3 pages, 3 figure

Charged impurity scattering limited low temperature resistivity of low density silicon inversion layers

We calculate within the Boltzmann equation approach the charged impurity scattering limited low temperature electronic resistivity of low density $n$-type inversion layers in Si MOSFET structures. We find a rather sharp quantum to classical crossover in the transport behavior in the $0 - 5$K temperature range, with the low density, low temperature mobility showing a strikingly strong non-monotonic temperature dependence, which may qualitatively explain the recently observed anomalously strong temperature dependent resistivity in low-density, high-mobility MOSFETs.Comment: 5 pages, 2 figures, will appear in PRL (12 July, 1999

Coexistence of Weak Localization and a Metallic Phase in Si/SiGe Quantum Wells

Magnetoresistivity measurements on p-type Si/SiGe quantum wells reveal the coexistence of a metallic behavior and weak localization. Deep in the metallic regime, pronounced weak localization reduces the metallic behavior around zero magnetic field without destroying it. In the insulating phase, a positive magnetoresistivity emerges close to B=0, possibly related to spin-orbit interactions.Comment: 4 pages, 3 figure

Parallel Magnetic Field Induced Transition in Transport in the Dilute Two-Dimensional Hole System in GaAs

A magnetic field applied parallel to the two-dimensional hole system in the GaAs/AlGaAs heterostructure, which is metallic in the absence of an external magnetic field, can drive the system into insulating at a finite field through a well defined transition. The value of resistivity at the transition is found to depend strongly on density

Classical versus Quantum Effects in the B=0 Conducting Phase in Two Dimensions

In the dilute two-dimensional electron system in silicon, we show that the temperature below which Shubnikov-de Haas oscillations become apparent is approximately the same as the temperature below which an exponential decrease in resistance is seen in B=0, suggesting that the anomalous behavior in zero field is observed only when the system is in a degenerate (quantum) state. The temperature dependence of the resistance is found to be qualitatively similar in B=0 and at integer Landau level filling factors.Comment: 3 pages, 3 figure

Universal scaling, beta function, and metal-insulator transitions

We demonstrate a universal scaling form of longitudinal resistance in the quantum critical region of metal-insulator transitions, based on numerical results of three-dimensional Anderson transitions (with and without magnetic field), two-dimensional quantum Hall plateau to insulator transition, as well as experimental data of the recently discovered two-dimensional metal-insulator transition. The associated reflection symmetry and a peculiar logarithmic form of the beta function exist over a wide range in which the resistance can change by more than one order of magnitude. Interesting implications for the two-dimensional metal-insulator transition are discussed.Comment: 4 pages, REVTEX, 4 embedded figures; minor corrections to figures and tex