40 research outputs found
Recommended from our members
Infra-red tunneling absorption in semiconductor double quantum wells in tilted magnetic fields
Using a linear response theory, interwell-tunneling absorption is calculated in a double-quantum-well structure with a wide center barrier in tilted magnetic fields. Tunneling absorption of infra-red photons occurs between the ground sublevels of the two quantum wells, with an energy difference that is tunable. In zero magnetic field, the absorption intensity decreases significantly as the linewidth increases with temperature. The absorption also depends strongly on the carrier densities of the wells. In magnetic fields, both the in-plane and perpendicular components of the field sensitively control and tune the absorption lineshape in very different ways, affecting the absorption threshold, the resonance energy of absorption, and the linewidth
Correlations, compressibility, and capacitance in double-quantum-well systems in the quantum Hall regime
In the quantum Hall regime, electronic correlations in double-layer
two-dimensional electron systems are strong because the kinetic energy is
quenched by Landau quantization. In this article we point out that these
correlations are reflected in the way the partitioning of charge between the
two-layers responds to a bias potential. We report on illustrative calculations
based on an unrestricted Hartree-Fock approximation which allows for
spontaneous inter-layer phase coherence. The possibility of studying
inter-layer correlations by capacitive coupling to separately contacted
two-dimensional layers is discussed in detail.Comment: RevTex style, 21 pages, 6 postscript figures in a separate file;
Phys. Rev. B (in press
Recommended from our members
Magnetic breakdown and Landau level spectra of a tunable double-quantum-well Fermi surface
By measuring longitudinal resistance, the authors map the Landau level spectra of double quantum wells as a function of both parallel (B{sub {parallel}}) and perpendicular (B{sub {perpendicular}}) magnetic fields. In this continuously tunable highly non-parabolic system, the cyclotron masses of the two Fermi surface orbits change in opposite directions with B{sub {parallel}}. This causes the two corresponding ladders of Landau levels formed at finite B{sub {perpendicular}} to exhibit multiple crossings. They also observe a third set of landau levels, independent of B{sub {parallel}}, which arise from magnetic breakdown of the Fermi surface. Both semiclassical and full quantum mechanical calculations show good agreement with the data
Magnetotunneling Between Two-dimensional Electron Gases in InAs-AlSb-GaSb Heterostructures
We have observed that the tunneling magnetoconductance between
two-dimensional (2D) electron gases formed at nominally identical InAs-AlSb
interfaces most often exhibits two sets of Shubnikov-de Haas oscillations with
almost the same frequency. This result is explained quantitatively with a model
of the conductance in which the 2D gases have different densities and can
tunnel between Landau levels with different quantum indices. When the epitaxial
growth conditions of the interfaces are optimized, the zero-bias
magnetoconductance shows a single set of oscillations, thus proving that the
asymmetry between the two electron gases can be eliminated.Comment: RevTeX format including 4 figures; submit for publicatio
Magnetoresistance and electronic structure of asymmetric GaAs/AlGaAs double quantum wells in the in-plane/tilted magnetic field
Bilayer two-dimensional electron systems formed by a thin barrier in the GaAs
buffer of a standard heterostructure were investigated by magnetotransport
measurements. In magnetic fields oriented parallel to the electron layers, the
magnetoresistance exhibits an oscillation associated with the depopulation of
the higher occupied subband and the field-induced transition into a decoupled
bilayer. Shubnikov-de Haas oscillations in slightly tilted magnetic fields
allow to reconstruct the evolution of the electron concentration in the
individual subbands as a function of the in-plane magnetic field. The
characteristics of the system derived experimentally are in quantitative
agreement with numerical self-consistent-field calculations of the electronic
structure.Comment: 6 pages, 5 figure
Phonon-drag effects on thermoelectric power
We carry out a calculation of the phonon-drag contribution to the
thermoelectric power of bulk semiconductors and quantum well structures for the
first time using the balance equation transport theory extended to the weakly
nonuniform systems. Introducing wavevector and phonon-mode dependent relaxation
times due to phonon-phonon interactions, the formula obtained can be used not
only at low temperatures where the phonon mean free path is determined by
boundary scattering, but also at high temperatures. In the linear transport
limit, is equivalent to the result obtained from the Boltzmann equation
with a relaxation time approximation. The theory is applied to experiments and
agreement is found between the theoretical predictions and experimental
results. The role of hot-electron effects in is discussed. The importance
of the contribution of to thermoelectric power in the hot-electron
transport condition is emphasized.Comment: 8 pages, REVTEX 3.0, 7 figures avilable upon reques
Localization corrections to the anomalous Hall effect in a ferromagnet
We calculate the localization corrections to the anomalous Hall conductivity
related to the contribution of spin-orbit scattering into the current vertex
(side-jump mechanism). We show that in contrast to the ordinary Hall effect,
there exists a nonvanishing localization correction to the anomalous Hall
resistivity. The correction to the anomalous Hall conductivity vanishes in the
case of side-jump mechanism, but is nonzero for the skew scattering. The total
correction to the nondiagonal conductivity related to both mechanisms, does not
compensate the correction to the diagonal conductivity.Comment: 7 pages with 7 figure
Evidence of Novel Quasiparticles in a Strongly Interacting Two-Dimensional Electron System: Giant Thermopower and Metallic Behaviour
We report thermopower () and electrical resistivity ()
measurements in low-density (10 m), mesoscopic two-dimensional
electron systems (2DESs) in GaAs/AlGaAs heterostructures at sub-Kelvin
temperatures. We observe at temperatures 0.7 K a linearly growing
as a function of temperature indicating metal-like behaviour. Interestingly
this metallicity is not Drude-like, showing several unusual characteristics: i)
the magnitude of exceeds the Mott prediction valid for non-interacting
metallic 2DESs at similar carrier densities by over two orders of magnitude;
and ii) in this regime is two orders of magnitude greater than
the quantum of resistance and shows very little temperature-dependence.
We provide evidence suggesting that these observations arise due to the
formation of novel quasiparticles in the 2DES that are not electron-like.
Finally, and show an intriguing decoupling in their
density-dependence, the latter showing striking oscillations and even sign
changes that are completely absent in the resistivity.Comment: QFS2012 Conference proceedings, Journal of Low Temperature Physics,
accepted (figure and discussion added upon referee suggestions