689 research outputs found
Universal Behaviour of Metal-Insulator Transitions in the p-SiGe System
Magnetoresistance measurements are presented for a strained p-SiGe quantum
well sample where the density is varied through the B=0 metal-insulator
transition. The close relationship between this transition, the high field Hall
insulator transition and the filling factor =3/2 insulating state is
demonstrated.Comment: 6 pages, 4 figures. Submitted to EP2DS XIII conference 199
On the thermal broadening of a quantum critical phase transition
The temperature dependence of an integer Quantum Hall effect transition is
studied in a sample where the disorder is dominated by short-ranged potential
scattering. At low temperatures the results are consistent with a
scaling behaviour and at higher temperatures by a linear
dependence similar to that reported in other material systems. It is shown that
the linear behaviour results from thermal broadening produced by the
Fermi-Dirac distribution function and that the temperature dependence over the
whole range depends only on the scaling parameter T
Metal Insulator transition at B=0 in p-SiGe
Observations are reported of a metal-insulator transition in a 2D hole gas in
asymmetrically doped strained SiGe quantum wells. The metallic phase, which
appears at low temperatures in these high mobility samples, is characterised by
a resistivity that decreases exponentially with decreasing temperature. This
behaviour, and the duality between resistivity and conductivity on the two
sides of the transition, are very similar to that recently reported for high
mobility Si-MOSFETs.Comment: 4 pages, REVTEX with 3 ps figure
Universality in an integer Quantum Hall transition
An integer Quantum Hall effect transition is studied in a modulation doped
p-SiGe sample. In contrast to most examples of such transitions the
longitudinal and Hall conductivities at the critical point are close to 0.5 and
1.5 (e^2/h), the theoretically expected values. This allows the extraction of a
scattering parameter, describing both conductivity components, which depends
exponentially on filling factor. The strong similarity of this functional form
to those observed for transitions into the Hall insulating state and for the
B=0 metal- insulator transition implies a universal quantum critical behaviour
for the transitions. The observation of this behaviour in the integer Quantum
Hall effect, for this particular sample, is attributed to the short-ranged
character of the potential associated with the dominant scatterers
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
Weak antilocalization in a strained InGaAs/InP quantum well structure
Weak antilocalization (WAL) effect due to the interference corrections to the
conductivity has been studied experimentally in a strained InGaAs/InP quantum
well structure. From measurements in tilted magnetic filed, it was shown that
both weak localization and WAL features depend only on the normal component of
the magnetic field for tilt angles less than 84 degrees. Weak antilocalization
effect showed non-monotonous dependence on the gate voltage which could not be
explained by either Rashba or Dresselhouse mechanisms of the spin-orbit
coupling. To describe magnetic field dependence of the conductivity, it was
necessary to assume that spin-orbit scattering time depends on the external
magnetic field which quenches the spin precession around effective, spin-orbit
related, magnetic fields.Comment: Presented at EP2DS 2003 (Nara), to be published in Physica
The Quantum Hall Effect and Inter-edge State Tunneling Within a Barrier
We have introduced a controllable nano-scale incursion into a potential
barrier imposed across a two-dimensional electron gas, and report on the
phenomena that we observe as the incursion develops. In the quantum Hall
regime, the conductance of this system displays quantized plateaus, broad
minima and oscillations. We explain these features and their evolution with
electrostatic potential geometry and magnetic field as a progression of current
patterns formed by tunneling between edge and localized states within the
barrier.Comment: RevTeX + 4 postscript figures. Self-unpacking uuencoded files.
Unpacking instructions are at the beginning of the files. To appear in
Physical Review
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