87 research outputs found
Mobility-Dependence of the Critical Density in Two-Dimensional Systems: An Empirical Relation
For five different electron and hole systems in two dimensions (Si MOSFET's,
p-GaAs, p-SiGe, n-GaAs and n-AlAs), the critical density, that marks the
onset of strong localization is shown to be a single power-law function of the
scattering rate deduced from the maximum mobility. The resulting curve
defines the boundary separating a localized phase from a phase that exhibits
metallic behavior. The critical density in the limit of infinite
mobility.Comment: 2 pages, 1 figur
Analysis of the resistance in p-SiGe over a wide temperature range
The temperature dependence of a system exhibiting a `metal-insulator
transition in two dimensions at zero magnetic field' (MIT) is studied up to
90K. Using a classical scattering model we are able to simulate the
non-monotonic temperature dependence of the resistivity in the metallic high
density regime. We show that the temperature dependence arises from a complex
interplay of metallic and insulating contributions contained in the calculation
of the scattering rate 1/\td(E,T), each dominating in a limited temperature
range.Comment: 4 pages with 5 figure
Analysis of the temperature-dependent quantum point contact conductance in view of the metal-insulator transition in two dimensions
The temperature dependence of the conductance of a quantum point contact has
been measured. The conductance as a function of the Fermi energy shows
temperature-independent fixed points, located at roughly multiple integers of
. Around the first fixed point at e/h, the experimental data for
different temperatures can been scaled onto a single curve. For pure thermal
smearing of the conductance steps, a scaling parameter of one is expected. The
measured scaling parameter, however, is significantly larger than 1. The
deviations are interpreted as a signature of the potential landscape of the
quantum point contact, and of the source-drain bias voltage. We relate our
results phenomenologically to the metal-insulator transition in two dimensions.Comment: 5 pages, 3 figure
Analysis of the Metallic Phase of Two-Dimensional Holes in SiGe in Terms of Temperature Dependent Screening
We find that temperature dependent screening can quantitatively explain the
metallic behaviour of the resistivity on the metallic side of the so-called
metal-insulator transition in p-SiGe. Interference and interaction effects
exhibit the usual insulating behaviour which is expected to overpower the
metallic background at sufficiently low temperatures. We find empirically that
the concept of a Fermi-liquid describes our data in spite of the large r_s = 8.Comment: 4 pages, 3 figure
Metallicity and its low temperature behavior in dilute 2D carrier systems
We theoretically consider the temperature and density dependent transport
properties of semiconductor-based 2D carrier systems within the RPA-Boltzmann
transport theory, taking into account realistic screened charged impurity
scattering in the semiconductor. We derive a leading behavior in the transport
property, which is exact in the strict 2D approximation and provides a zeroth
order explanation for the strength of metallicity in various 2D carrier
systems. By carefully comparing the calculated full nonlinear temperature
dependence of electronic resistivity at low temperatures with the corresponding
asymptotic analytic form obtained in the limit, both within the
RPA screened charged impurity scattering theory, we critically discuss the
applicability of the linear temperature dependent correction to the low
temperature resistivity in 2D semiconductor structures. We find quite generally
that for charged ionized impurity scattering screened by the electronic
dielectric function (within RPA or its suitable generalizations including local
field corrections), the resistivity obeys the asymptotic linear form only in
the extreme low temperature limit of . We point out the
experimental implications of our findings and discuss in the context of the
screening theory the relative strengths of metallicity in different 2D systems.Comment: We have substantially revised this paper by adding new materials and
figures including a detailed comparison to a recent experimen
Compressibility of a two-dimensional hole gas in tilted magnetic field
We have measured compressibility of a two-dimensional hole gas in
p-GaAs/AlGaAs heterostructure, grown on a (100) surface, in the presence of a
tilted magnetic field. It turns out that the parallel component of magnetic
field affects neither the spin splitting nor the density of states. We conclude
that: (a) g-factor in the parallel magnetic field is nearly zero in this
system; and (b) the level of the disorder potential is not sensitive to the
parallel component of the magnetic field
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
The relative importance of electron-electron interactions compared to disorder in the two-dimensional "metallic" state
The effect of substrate bias and surface gate voltage on the low temperature
resistivity of a Si-MOSFET is studied for electron concentrations where the
resistivity increases with increasing temperature. This technique offers two
degrees of freedom for controlling the electron concentration and the device
mobility, thereby providing a means to evaluate the relative importance of
electron-electron interactions and disorder in this so-called ``metallic''
regime. For temperatures well below the Fermi temperature, the data obey a
scaling law where the disorder parameter (), and not the
concentration, appears explicitly. This suggests that interactions, although
present, do not alter the Fermi-liquid properties of the system fundamentally.
Furthermore, this experimental observation is reproduced in results of
calculations based on temperature-dependent screening, in the context of
Drude-Boltzmann theory.Comment: 5 pages, 6 figure
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