1,658 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
A New Transport Regime in the Quantum Hall Effect
This paper describes an experimental identification and characterization of a
new low temperature transport regime near the quantum Hall-to-insulator
transition. In this regime, a wide range of transport data are compactly
described by a simple phenomenological form which, on the one hand, is
inconsistent with either quantum Hall or insulating behavior and, on the other
hand, is also clearly at odds with a quantum-critical, or scaling, description.
We are unable to determine whether this new regime represents a clearly defined
state or is a consequence of finite temperature and sample-size measurements.Comment: Revtex, 3 pages, 2 figure
The Quantized Hall Insulator: A New Insulator in Two-Dimensions
Quite generally, an insulator is theoretically defined by a vanishing
conductivity tensor at the absolute zero of temperature. In classical
insulators, such as band insulators, vanishing conductivities lead to diverging
resistivities. In other insulators, in particular when a high magnetic field
(B) is added, it is possible that while the magneto-resistance diverges, the
Hall resistance remains finite, which is known as a Hall insulator. In this
letter we demonstrate experimentally the existence of another, more exotic,
insulator. This insulator, which terminates the quantum Hall effect series in a
two-dimensional electron system, is characterized by a Hall resistance which is
approximately quantized in the quantum unit of resistance h/e^2. This insulator
is termed a quantized Hall insulator. In addition we show that for the same
sample, the insulating state preceding the QHE series, at low-B, is of the HI
kind.Comment: 4 page
The quantized Hall effect in the presence of resistance fluctuations
We present an experimental study of mesoscopic, two-dimensional electronic
systems at high magnetic fields. Our samples, prepared from a low-mobility
InGaAs/InAlAs wafer, exhibit reproducible, sample specific, resistance
fluctuations. Focusing on the lowest Landau level we find that, while the
diagonal resistivity displays strong fluctuations, the Hall resistivity is free
of fluctuations and remains quantized at its value, . This is
true also in the insulating phase that terminates the quantum Hall series.
These results extend the validity of the semicircle law of conductivity in the
quantum Hall effect to the mesoscopic regime.Comment: Includes more data, changed discussio
Evidence for a Finite Temperature Insulator
In superconductors the zero-resistance current-flow is protected from
dissipation at finite temperatures (T) by virtue of the short-circuit condition
maintained by the electrons that remain in the condensed state. The recently
suggested finite-T insulator and the "superinsulating" phase are different
because any residual mechanism of conduction will eventually become dominant as
the finite-T insulator sets-in. If the residual conduction is small it may be
possible to observe the transition to these intriguing states. We show that the
conductivity of the high magnetic-field insulator terminating superconductivity
in amorphous indium-oxide exhibits an abrupt drop, and seem to approach a zero
conductance at T<0.04 K. We discuss our results in the light of theories that
lead to a finite-T insulator
Phase Diagram of Integer Quantum Hall Effect
The phase diagram of integer quantum Hall effect is numerically determined in
the tight-binding model, which can account for overall features of recently
obtained experimental phase diagram. In particular, the quantum Hall plateaus
are terminated by two distinct insulating phases, characterized by the Hall
resistance with classic and quantized values, respectively, which is also in
good agreement with experiments.Comment: 4 pages, RevTex, 4 PostScript figures; one new figure is added; minor
modifications in the tex
Universality in the Crossover between Edge Channel and Bulk Transport in the Quantum Hall Regime
We present a new theoretical approach for the integer quantum Hall effect,
which is able to describe the inter-plateau transitions as well as the
transition to the Hall insulator. We find two regimes (metallic and insulator
like) of the top Landau level, in which the dissipative bulk current appears in
different directions. The regimes are separated by a temperature invariant
point.Comment: 4 page, 2 eps figures included, submitte
Universality at integer quantum Hall transitions
We report in this paper results of experimental and theoretical studies of
transitions between different integer quantum Hall phases, as well as
transition between the insulating phase and quantum Hall phases at high
magnetic fields. We focus mainly on universal properties of the transitions. We
demonstrate that properly defined conductivity tensor is universal at the
transitions. We also present numerical results of a non-interacting electron
model, which suggest that the Thouless conductance is universal at integer
quantum Hall transitions, just like the conductivity tensor. Finite temperature
and system size effects near the transition point are also studied.Comment: 20 pages, 15 figure
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