53 research outputs found
Low-field magnetoresistance in GaAs 2D holes
We report low-field magnetotransport data in two-dimensional hole systems in
GaAs/AlGaAs heterostructures and quantum wells, in a large density range, cm, with primary focus on
samples grown on (311)A GaAs substrates. At high densities, cm, we observe a remarkably strong positive magnetoresistance.
It appears in samples with an anisotropic in-plane mobility and predominantly
along the low-mobility direction, and is strongly dependent on the
perpendicular electric field and the resulting spin-orbit interaction induced
spin-subband population difference. A careful examination of the data reveals
that the magnetoresistance must result from a combination of factors including
the presence of two spin-subbands, a corrugated quantum well interface which
leads to the mobility anisotropy, and possibly weak anti-localization. None of
these factors can alone account for the observed positive magnetoresistance. We
also present the evolution of the data with density: the magnitude of the
positive magnetoresistance decreases with decreasing density until, at the
lowest density studied ( cm), it vanishes and is
replaced by a weak negative magnetoresistance.Comment: 8 pages, 8 figure
The effect of inter-edge Coulomb interactions on the transport between quantum Hall edge states
In a recent experiment, Milliken {\em et al.} demonstrated possible evidence
for a Luttinger liquid through measurements of the tunneling conductance
between edge states in the quantum Hall plateau. However, at low
temperatures, a discrepancy exists between the theoretical predictions based on
Luttinger liquid theory and experiment. We consider the possibility that this
is due to long-range Coulomb interactions which become dominant at low
temperatures. Using renormalization group methods, we calculate the cross-over
behaviour from Luttinger liquid to the Coulomb interaction dominated regime.
The cross-over behaviour thus obtained seems to resolve one of the
discrepancies, yielding good agreement with experiment.Comment: 4 pages, RevTex, 2 postscript figures, tex file and figures have been
uuencode
Charge Density Wave Behaviour of the Integer Quantum Hall Effect Edge States
We analyze the effect that the Coulomb interaction has on the edge
excitations of an electron gas confined in a bar of thickness , and in
presence of a magnetic field corresponding to filling factor 1 Quantum Hall
effect. We find that the long-range interaction between the edges leads the
system to a ground state with a quasi-long range order, similar to a Charge
Density Wave. The spectral density of states vanishes at zero frequency, and
increases with frequency faster than any power law, being the conductance of a
infinite long system zero.Comment: 10 pages, latex, 3 figures available by FAX upon request from
[email protected]
In-plane magnetic field-induced spin polarization and transition to insulating behavior in two-dimensional hole systems
Using a novel technique, we make quantitative measurements of the spin
polarization of dilute (3.4 to 6.8*10^{10} cm^{-2}) GaAs (311)A two-dimensional
holes as a function of an in-plane magnetic field. As the field is increased
the system gradually becomes spin polarized, with the degree of spin
polarization depending on the orientation of the field relative to the crystal
axes. Moreover, the behavior of the system turns from metallic to insulating
\textit{before} it is fully spin polarized. The minority-spin population at the
transition is ~8*10^{9} cm^{-2}, close to the density below which the system
makes a transition to an insulating state in the absence of a magnetic field.Comment: 4 pages with figure
Inter-Edge interaction in the Quantum Hall Effect
We consider effects of the interaction between electrons drifting along the
opposite sides of a narrow sample under the conditions of the quantum Hall
effect. A spatial variation of this interaction leads to backward scattering of
collective excitations propagating along the edges. Experiments on propagation
of the edge modes in samples with constrictions may give information about the
strength of the inter-edge electron interaction in the quantum Hall regime.Comment: 12 Pages, Latex, Accepted for publication in PRL
Non-monotonic magnetic field and density dependence of in-plane magnetoresistance in dilute two-dimensional holes in GaAs/AlGaAs
We studied low temperature (T=50mK) in-plane magnetoresistance of a dilute
two-dimensional hole system in GaAs/AlGaAs heterostructure that exhibits an
apparent metal-insulator transition. We found an anisotropic magnetoresistance,
which changes dramatically at high in-plane fields (B_{\parallel}\agt5T) as
the hole density is varied. At high densities where the system behaves metallic
at , the transverse magnetoresistance is larger than the
longitudinal magnetoresistance. With decreasing the hole density the difference
becomes progressively smaller, and at densities near the "critical" density and
lower, the longitudinal magnetoresistance becomes larger than the transverse
magnetoresistance
Repulsion of Single-well Fundamental Edge Magnetoplasmons in Double Quantum Wells
A {\it microscopic} treatment of fundamental edge magnetoplasmons (EMPs)
along the edge of a double quantum well (DQW) is presented for strong magnetic
fields, low temperatures, and total filling factor \nu=2. It is valid for
lateral confining potentials that Landau level (LL) flattening can be
neglected. The cyclotron and Zeeman energies are assumed larger than the DQW
energy splitting \sqrt{\Delta^2 +4T^2}, where \Delta is the splitting of the
isolated wells and T the tunneling matrix element. %hen calculated unperturbed
density profile is sharp at the edge. Using a random-phase approximation (RPA),
which includes local and nonlocal contributions to the current density, it is
shown that for negligible tunnel coupling 2T << \Delta the inter-well Coulomb
coupling leads to two DQW fundamental EMPs which are strongly renormalized in
comparison with the decoupled, single-well fundamental EMP. These DQW modes can
be modified further upon varying the inter-well distance d, along the z axis,
and/or the separation of the wells' edges \Delta y along the y axis. The charge
profile of the {\it fast} and {\it slow} DQW mode varies, respectively, in an
{\it acoustic} and {\it optical} manner along the y axis and is not smooth on
the \ell_{0} scale. For strong tunneling \Delta\alt 2T these DQW modes are
essentially modified when \Delta is changed by applying a transverse electric
field to the DQW.Comment: Text 18 pages in Latex/Revtex/Preprint format, 2 Postscript figure
Electronic Spectral Functions for Quantum Hall Edge States
We have evaluated wavevector-dependent electronic spectral functions for
integer and fractional quantum Hall edge states using a chiral Luttinger liquid
model. The spectral functions have a finite width and a complicated line shape
because of the long-range of the Coulomb interaction. We discuss the
possibility of probing these line shapes in vertical tunneling experiments.Comment: 4 pages, RevTex, two figures included, to appear as a Rapid
Communication in PRB; we updated references which have recently appeared in
print and were cited as preprints in our ealier submissio
Plasmon Modes and Correlation Functions in Quantum Wires and Hall Bars
We present microscopic derivations of the one-dimensional low-energy boson
effective Hamiltonians of quantum wire and quantum Hall bar systems. The
quantum Hall system is distinguished by its spatial separation of oppositely
directed electrons. We discuss qualitative differences in the plasmon
collective mode dispersions and the ground state correlation functions of the
two systems which are consequences of this difference. The slowly-decaying
quasi-solid correlations expected in a quantum wire are strongly suppressed in
quantum Hall bar systems.Comment: 7 pages, RevTex, 3 figures and 1 table included; references updated
and minor typos correcte
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