667 research outputs found
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
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
"Forbidden" transitions between quantum Hall and insulating phases in p-SiGe heterostructures
We show that in dilute metallic p-SiGe heterostructures, magnetic field can
cause multiple quantum Hall-insulator-quantum Hall transitions. The insulating
states are observed between quantum Hall states with filling factors \nu=1 and
2 and, for the first time, between \nu=2 and 3 and between \nu=4 and 6. The
latter are in contradiction with the original global phase diagram for the
quantum Hall effect. We suggest that the application of a (perpendicular)
magnetic field induces insulating behavior in metallic p-SiGe heterostructures
in the same way as in Si MOSFETs. This insulator is then in competition with,
and interrupted by, integer quantum Hall states leading to the multiple
re-entrant transitions. The phase diagram which accounts for these transition
is similar to that previously obtained in Si MOSFETs thus confirming its
universal character
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
Coleridge, Sara
An encylopaedia article on the life and writings of Sara Coleridge (1802-1852), for an online work of reference and scholarshi
Duality and Non-linear Response for Quantum Hall Systems
We derive the implications of particle-vortex duality for the electromagnetic
response of Quantum Hall systems beyond the linear-response regime. This
provides a first theoretical explanation of the remarkable duality which has
been observed in the nonlinear regime for the electromagnetic response of
Quantum Hall systems.Comment: 7 pages, 1 figure, typeset in LaTe
In-plane Magnetoconductivity of Si-MOSFET's: A Quantitative Comparison between Theory and Experiment
For densities above cm in the strongly
interacting system of electrons in two-dimensional silicon inversion layers,
excellent agreement between experiment and the theory of Zala, Narozhny and
Aleiner is obtained for the response of the conductivity to a magnetic field
applied parallel to the plane of the electrons. However, the Fermi liquid
parameter and the valley splitting obtained from
fits to the magnetoconductivity, although providing qualitatively correct
behavior (including sign), do not yield quantitative agreement with the
temperature dependence of the conductivity in zero magnetic field. Our results
suggest the existence of additional scattering processes not included in the
theory in its present form
Electron spin-orbit splitting in InGaAs/InP quantum well studied by means of the weak antilocalization and spin-zero effects in tilted magnetic fields
The coupling between Zeeman spin splitting and Rashba spin-orbit terms has
been studied experimentally in a gated InGaAs/InP quantum well structure by
means of simultaneous measurements of the weak antilocalization (WAL) effect
and beating in the SdH oscillations. The strength of the Zeeman splitting was
regulated by tilting the magnetic field with the spin-zeros in the SdH
oscillations, which are not always present, being enhanced by the tilt. In
tilted fields the spin-orbit and Zeeman splittings are not additive, and a
simple expression is given for the energy levels. The Rashba parameter and the
electron g-factor were extracted from the position of the spin zeros in tilted
fields. A good agreement is obtained for the spin-orbit coupling strength from
the spin-zeros and weak antilocalization measurements.Comment: Accepted for publication in Semiconductors Science and Technolog
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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