Tunneling Conductance Between Parallel Two Dimensional Electron Systems

We derive and evaluate expressions for the low temperature {\it dc} equilibrium tunneling conductance between parallel two-dimensional electron systems. Our theory is based on a linear-response formalism and on impurity-averaged perturbation theory. The disorder broadening of features in the dependence of tunneling conductance on sheet densities and in-plane magnetic field strengths is influenced both by the finite lifetime of electrons within the wells and by non-momentum-conserving tunneling events. Disorder vertex corrections are important only for weak in-plane magnetic fields and strong interwell impurity-potential correlations. We comment on the basis of our results on the possibility of using tunneling measurements to determine the lifetime of electrons in the quantum wells.Comment: 14 pages, 5 Fig. not included, revtex, IUcm92-00

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]

Mesoscopic effects in tunneling between parallel quantum wires

We consider a phase-coherent system of two parallel quantum wires that are coupled via a tunneling barrier of finite length. The usual perturbative treatment of tunneling fails in this case, even in the diffusive limit, once the length L of the coupling region exceeds a characteristic length scale L_t set by tunneling. Exact solution of the scattering problem posed by the extended tunneling barrier allows us to compute tunneling conductances as a function of applied voltage and magnetic field. We take into account charging effects in the quantum wires due to applied voltages and find that these are important for 1D-to-1D tunneling transport.Comment: 8 pages, 7 figures, improved Figs., added Refs. and appendix, to appear in Phys. Rev.

Scanning Capacitance Microscopy Investigations of Focused Ion Beam Damage in Silicon

In this article, we explore the application of Scanning Capacitance Microscopy (SCM) for studying focused ion beam (FIB) induced damage in silicon. We qualitatively determine the technologically important beam shape by measuring the SCM image of FIB processed implantation spots and by comparison of topographical and SCM data. Further, we investigate the question how deep impinging ions generate measurable damage below the silicon surface. For this purpose, trenches were manufactured using FIB and analyzed by SCM in cross sectional geometry

Inhomogeneous broadening of tunneling conductance in double quantum wells

The lineshape of the tunneling conductance in double quantum wells with a large-scale roughness of heterointerfaces is investigated. Large-scale variations of coupled energy levels and scattering due to the short-range potential are taken into account. The interplay between the inhomogeneous broadening, induced by the non-screened part of large-scale potential, and the homogeneous broadening due to the scattering by short-range potentials is considered. It is shown that the large inhomogeneous broadening can be strongly modified by nonlocal effects involved in the proposed mechanism of inhomogeneity. Related change of lineshape of the resonant tunneling conductance between Gaussian and Lorentzian peaks is described. The theoretical results agree quite well with experimental data.Comment: 11 pages, 5 figure

Magnetotunneling spectroscopy of mesoscopic correlations in two-dimensional electron systems

An approach to experimentally exploring electronic correlation functions in mesoscopic regimes is proposed. The idea is to monitor the mesoscopic fluctuations of a tunneling current flowing between the two layers of a semiconductor double-quantum-well structure. From the dependence of these fluctuations on external parameters, such as in-plane or perpendicular magnetic fields, external bias voltages, etc., the temporal and spatial dependence of various prominent correlation functions of mesoscopic physics can be determined. Due to the absence of spatially localized external probes, the method provides a way to explore the interplay of interaction and localization effects in two-dimensional systems within a relatively unperturbed environment. We describe the theoretical background of the approach and quantitatively discuss the behavior of the current fluctuations in diffusive and ergodic regimes. The influence of both various interaction mechanisms and localization effects on the current is discussed. Finally a proposal is made on how, at least in principle, the method may be used to experimentally determine the relevant critical exponents of localization-delocalization transitions.Comment: 15 pages, 3 figures include

Observation of a Linearly Dispersing Collective Mode in a Quantum Hall Ferromagnet

Double layer two-dimensional electron systems can exhibit a fascinating collective phase believed to exhibit both quantum ferromagnetism and excitonic superfluidity. This unusual phase has recently been found to exhibit tunneling phenomena reminiscent of the Josephson effect. A key element of the theoretical understanding of this bizarre quantum fluid is the existence of linearly dispersing Goldstone collective modes. Using the method of tunneling spectroscopy, we have demonstrated the existence of these modes. We find the measured velocity to be in reasonable agreement with theoretical estimates.Comment: 5 pages, 4 figures; accepted for publication in PRL. Contains new data, a new figure, and a new titl

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

Enhancement of tunneling from a correlated 2D electron system by a many-electron Mossbauer-type recoil in a magnetic field

We consider the effect of electron correlations on tunneling from a 2D electron layer in a magnetic field parallel to the layer. A tunneling electron can exchange its momentum with other electrons, which leads to an exponential increase of the tunneling rate compared to the single-electron approximation. Explicit results are obtained for a Wigner crystal. They provide a qualitative and quantitative explanation of the data on electrons on helium. We also discuss tunneling in semiconductor heterostructures.Comment: published version, 4 pages, 2 figures, RevTeX 3.

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 $B_{\parallel}$ and interwell spacing $d$. This is done for variety of incompressible states including a pair of $\nu=1/3$ layers ([330]), pair of $\nu=1/5$ 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