73 research outputs found
Spin polarization of strongly interacting 2D electrons: the role of disorder
In high-mobility silicon MOSFET's, the inferred indirectly from
magnetoconductance and magnetoresistance measurements with the assumption that
are in surprisingly good agreement with obtained by
direct measurement of Shubnikov-de Haas oscillations. The enhanced
susceptibility exhibits critical behavior of the form
. We examine the significance of the field
scale derived from transport measurements, and show that this field
signals the onset of full spin polarization only in the absence of disorder.
Our results suggest that disorder becomes increasingly important as the
electron density is reduced toward the transition.Comment: 4 pages, 3 figure
Can mesoscopic fluctuations reverse the supercurrent through a disordered Josephson junction?
We calculate the Josephson coupling energy (related to the
supercurrent ) for a disordered normal metal between
two superconductors with a phase difference . We demonstrate that the
symmetry of the scattering matrix of non-interacting quasiparticles in zero
magnetic field implies that has a minimum at . A maximum
(that would lead to a -junction or negative superfluid density) is
excluded for any realization of the disorder.Comment: 2 page
Exact analytical expression for magnetoresistance using quantum groups
We obtain an exact analytical expression for magnetoresistance using
noncommutative geometry and quantum groups.Then we will show that there is a
deep relationship between magnetoresistance and the quantum group ,
from which we understand the quantum interpretation of the quantum corrections
to the conductivity.Comment: 8 pages, 3 figures, replaced with the version published in Physics
Letters
Effect of Nyquist Noise on the Nyquist Dephasing Rate in 2d Electron Systems
We measure the effect of externally applied broadband Nyquist noise on the
intrinsic Nyquist dephasing rate of electrons in a two-dimensional electron gas
at low temperatures. Within the measurement error, the phase coherence time is
unaffected by the externally applied Nyquist noise, including applied noise
temperatures of up to 300 K. The amplitude of the applied Nyquist noise from
100 MHz to 10 GHz is quantitatively determined in the same experiment using a
microwave network analyzer.Comment: 5 pages, 4 figures. Author affiliation clarified; acknowledgements
modified. Replacement reason clarifie
Interaction Corrections to Two-Dimensional Hole Transport in Large Limit
The metallic conductivity of dilute two-dimensional holes in a GaAs HIGFET
(Heterojunction Insulated-Gate Field-Effect Transistor) with extremely high
mobility and large is found to have a linear dependence on temperature,
consistent with the theory of interaction corrections in the ballistic regime.
Phonon scattering contributions are negligible in the temperature range of our
interest, allowing comparison between our measured data and theory without any
phonon subtraction. The magnitude of the Fermi liquid interaction parameter
determined from the experiment, however, decreases with
increasing for r_{s}\agt22, a behavior unexpected from existing
theoretical calculations valid for small .Comment: 6 pages, 4 figure
Fate of the extended states in a vanishing magnetic field: the role of spins in strongly-interacting 2D electron systems
In non-interacting or weakly-interacting 2D electron systems, the energy of
the extended states increases as the perpendicular magnetic field approaches
zero: the extended states "float up" in energy, giving rise to an insulator.
However, in those 2D systems where metallic conductivity has been recently
observed in zero magnetic field, the energy of the extended states remains
constant or even decreases as B -> 0, thus allowing conduction in the limit of
zero temperature. Here we show that aligning the electrons' spins causes the
extended states to once more "float up" in energy in the vanishing
perpendicular magnetic field, as they do for non- or weakly-interacting
electrons. The difference between extended states that float up (an insulator)
or remain finite (a metal) is thus tied to the existence of the spins
Hall Coefficient in an Interacting Electron Gas
The Hall conductivity in a weak homogeneous magnetic field, , is calculated. We have shown that to leading order in
the Hall coefficient is not renormalized by the
electron-electron interaction. Our result explains the experimentally observed
stability of the Hall coefficient in a dilute electron gas not too close to the
metal-insulator transition. We avoid the currently used procedure that
introduces an artificial spatial modulation of the magnetic field. The problem
of the Hall effect is reformulated in a way such that the magnetic flux
associated with the scattering process becomes the central element of the
calculation.Comment: 23 pages, 15 figure
Two-Component Scaling near the Metal-Insulator Bifurcation in Two-Dimensions
We consider a two-component scaling picture for the resistivity of
two-dimensional (2D) weakly disordered interacting electron systems at low
temperature with the aim of describing both the vicinity of the bifurcation and
the low resistance metallic regime in the same framework. We contrast the
essential features of one-component and two-component scaling theories. We
discuss why the conventional lowest order renormalization group equations do
not show a bifurcation in 2D, and a semi-empirical extension is proposed which
does lead to bifurcation. Parameters, including the product , are
determined by least squares fitting to experimental data. An excellent
description is obtained for the temperature and density dependence of the
resistance of silicon close to the separatrix. Implications of this
two-component scaling picture for a quantum critical point are discussed.Comment: 7 pages, 1 figur
Experimental study of weak antilocalization effect in a high mobility InGaAs/InP quantum well
The magnetoresistance associated with quantum interference corrections in a
high mobility, gated InGaAs/InP quantum well structure is studied as a function
of temperature, gate voltage, and angle of the tilted magnetic field.
Particular attention is paid to the experimental extraction of phase-breaking
and spin-orbit scattering times when weak anti- localization effects are
prominent. Compared with metals and low mobility semiconductors the
characteristic magnetic field in high mobility
samples is very small and the experimental dependencies of the interference
effects extend to fields several hundreds of times larger. Fitting experimental
results under these conditions therefore requires theories valid for arbitrary
magnetic field. It was found, however, that such a theory was unable to fit the
experimental data without introducing an extra, empirical, scale factor of
about 2. Measurements in tilted magnetic fields and as a function of
temperature established that both the weak localization and the weak
anti-localization effects have the same, orbital origin. Fits to the data
confirmed that the width of the low field feature, whether a weak localization
or a weak anti-localization peak, is determined by the phase-breaking time and
also established that the universal (negative) magnetoresistance observed in
the high field limit is associated with a temperature independent spin-orbit
scattering time.Comment: 13 pages including 10 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
- …