63 research outputs found
Lifetime of Two-Dimensional Electrons Measured by Tunneling Spectroscopy
For electrons tunneling between parallel two-dimensional electron systems,
conservation of in-plane momentum produces sharply resonant current-voltage
characteristics and provides a uniquely sensitive probe of the underlying
electronic spectral functions. We report here the application of this technique
to accurate measurements of the temperature dependence of the electron-electron
scattering rate in clean two-dimensional systems. Our results are in
qualitative agreement with existing calculations.Comment: file in REVTEX format produces 11 pages, 3 figures available from
[email protected]
Tunneling Between a Pair of Parallel Hall Droplets
In this paper, we examine interwell tunneling between a pair of fractional
quantum Hall liquids in a double quantum well system in a tilted magnetic
field. Using a variational Monte Carlo method, we calculate moments of the
intra-Landau level tunneling spectrum as a function of in-plane field component
and interwell spacing . This is done for variety of
incompressible states including a pair of layers ([330]), pair of
layers ([550]), and Halperin's [331] state. The results suggest a
technique to extract interwell correlations from the tunneling spectral data.Comment: 21 pages and 8 figures (included), RevTeX, preprint no. UCSDCU
Electron-electron interactions and two-dimensional - two-dimensional tunneling
We derive and evaluate expressions for the dc tunneling conductance between
interacting two-dimensional electron systems at non-zero temperature. The
possibility of using the dependence of the tunneling conductance on voltage and
temperature to determine the temperature-dependent electron-electron scattering
rate at the Fermi energy is discussed. The finite electronic lifetime produced
by electron-electron interactions is calculated as a function of temperature
for quasiparticles near the Fermi circle. Vertex corrections to the random
phase approximation substantially increase the electronic scattering rate. Our
results are in an excellent quantitative agreement with experiment.Comment: Revtex style, 21 pages and 8 postscript figures in a separate file;
Phys. Rev. B (in press
Tunneling transverse to a magnetic field, and how it occurs in correlated 2D electron systems
We investigate tunneling decay in a magnetic field. Because of broken
time-reversal symmetry, the standard WKB technique does not apply. The decay
rate and the outcoming wave packet are found from the analysis of the set of
the particle Hamiltonian trajectories and its singularities in complex space.
The results are applied to tunneling from a strongly correlated 2D electron
system in a magnetic field parallel to the layer. We show in a simple model
that electron correlations exponentially strongly affect the tunneling rate.Comment: 4 pages, 3 figure
Tunneling Between Parallel Two-Dimensional Electron Gases
The tunneling between two parallel two-dimensional electron gases has been
investigated as a function of temperature , carrier density , and the
applied perpendicular magnetic field . In zero magnetic field the
equilibrium resonant lineshape is Lorentzian, reflecting the Lorentzian form of
the spectral functions within each layer. From the width of the tunneling
resonance the lifetime of the electrons within a 2DEG has been measured as a
function of and , giving information about the density dependence of the
electron-impurity scattering and the temperature dependence of the
electron-electron scattering. In a magnetic field there is a general
suppression of equilibrium tunneling for fields above T. A gap in the
tunneling density of states has been measured over a wide range of magnetic
fields and filling factors, and various theoretical predictions have been
examined. In a strong magnetic field, when there is only one partially filled
Landau level in each layer, the temperature dependence of the conductance
characteristics has been modeled with a double-Gaussian spectral density.Comment: LaTeX requires REVTeX macros. Eighteen pages. Fourteen postscript
figures are included. (All figures have been bitmapped to save space. The
original can be requested by email from [email protected]). Accepted for
publication in Phys. Rev.
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
Itinerant Electron Ferromagnetism in the Quantum Hall Regime
We report on a study of the temperature and Zeeman-coupling-strength
dependence of the one-particle Green's function of a two-dimensional (2D)
electron gas at Landau level filling factor where the ground state is
a strong ferromagnet. Our work places emphasis on the role played by the
itinerancy of the electrons, which carry the spin magnetization and on
analogies between this system and conventional itinerant electron ferromagnets.
We discuss the application to this system of the self-consistent Hartree-Fock
approximation, which is analogous to the band theory description of metallic
ferromagnetism and fails badly at finite temperatures because it does not
account for spin-wave excitations. We go beyond this level by evaluating the
one-particle Green's function using a self-energy, which accounts for
quasiparticle spin-wave interactions. We report results for the temperature
dependence of the spin magnetization, the nuclear spin relaxation rate, and
2D-2D tunneling conductances. Our calculations predict a sharp peak in the
tunneling conductance at large bias voltages with strength proportional to
temperature. We compare with experiment, where available, and with predictions
based on numerical exact diagonalization and other theoretical approaches.Comment: 29 pages, 20 figure
Signatures of phonon and defect-assisted tunneling in planar metal-hexagonal boron nitride-graphene junctions
Electron tunneling spectroscopy measurements on van der Waals heterostructures consisting of metal and graphene (or graphite) electrodes separated by atomically thin hexagonal boron nitride tunnel barriers are reported. The tunneling conductance, dI/dV, at low voltages is relatively weak, with a strong enhancement reproducibly observed to occur at around |V| ≈ 50 mV. While the weak tunneling at low energies is attributed to the absence of substantial overlap, in momentum space, of the metal and graphene Fermi surfaces, the enhancement at higher energies signals the onset of inelastic processes in which phonons in the heterostructure provide the momentum necessary to link the Fermi surfaces. Pronounced peaks in the second derivative of the tunnel current, d2I/dV2, are observed at voltages where known phonon modes in the tunnel junction have a high density of states. In addition, features in the tunneling conductance attributed to single electron charging of nanometer-scale defects in the boron nitride are also observed in these devices. The small electronic density of states of graphene allows the charging spectra of these defect states to be electrostatically tuned, leading to “Coulomb diamonds” in the tunneling conductance
Tunneling decay in a magnetic field
We provide a semiclassical theory of tunneling decay in a magnetic field and
a three-dimensional potential of a general form. Because of broken
time-reversal symmetry, the standard WKB technique has to be modified. The
decay rate is found from the analysis of the set of the particle Hamiltonian
trajectories in complex phase space and time. In a magnetic field, the
tunneling particle comes out from the barrier with a finite velocity and behind
the boundary of the classically allowed region. The exit location is obtained
by matching the decaying and outgoing WKB waves at a caustic in complex
configuration space. Different branches of the WKB wave function match on the
switching surface in real space, where the slope of the wave function sharply
changes. The theory is not limited to tunneling from potential wells which are
parabolic near the minimum. For parabolic wells, we provide a bounce-type
formulation in a magnetic field. The theory is applied to specific models which
are relevant to tunneling from correlated two-dimensional electron systems in a
magnetic field parallel to the electron layer.Comment: 16 pages, 11 figure
Spontaneous Coherence and Collective Modes in Double-Layer Quantum Dot Systems
We study the ground state and the collective excitations of
parabolically-confined double-layer quantum dot systems in a strong magnetic
field. We identify parameter regimes where electrons form maximum density
droplet states, quantum-dot analogs of the incompressible states of the bulk
integer quantum Hall effect. In these regimes the Hartree-Fock approximation
and the time-dependent Hartree-Fock approximations can be used to describe the
ground state and collective excitations respectively. We comment on the
relationship between edge excitations of dots and edge magneto-plasmon
excitations of bulk double-layer systems.Comment: 20 pages (figures included) and also available at
http://fangio.magnet.fsu.edu/~jhu/Paper/qdot_cond.ps, replaced to fix figure
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