Classical tunneling

A classical representation of an extended body over barriers of height greater than the energy of the incident body is shown to have many features in common with quantum tunneling as the center-of-mass literally goes through the barrier. It is even classically possible to penetrate any finite barrier with a body of arbitrarily low energy if the body is sufficiently long. A distribution of body lengths around the de Broglie wavelength leads to reasonable agreement with the quantum transmission coefficient.     

Dissipative tunneling

Zeitschrift für Physik B Condensed Matter - The rate of escape of a metastable state is studied in a temperature regime where quantum tunneling acts as the rate limiting process. The particle...     

Fluctuation dominated Josephson tunneling with a scanning tunneling microscope

We demonstrate Josephson tunneling in vacuum tunnel junctions formed between a superconducting scanning tunneling microscope tip and a Pb film, for junction resistances in the range 50-300 k Omega. We show that the superconducting phase dynamics is dominated by thermal fluctuations, and that the Josephson current appears as a peak centered at small finite voltage. In the presence of microwave fields ( f = 15.0 GHz) the peak decreases in magnitude and shifts to higher voltages with increasing rf power, in agreement with theory.     

Vacuum phonon tunneling

Field-induced phonon tunneling, a previously unknown mechanism of interfacial thermal transport, has been revealed by ultrahigh vacuum inelastic scanning tunneling microscopy (STM). Using thermally broadened Fermi-Dirac distribution in the STM tip as in situ atomic-scale thermometer we found that thermal vibrations of the last tip atom are effectively transmitted to sample surface despite few angstroms wide vacuum gap. We show that phonon tunneling is driven by interfacial electric field and thermally vibrating image charges, and its rate is enhanced by surface electron-phonon interaction.     

Inelastic electron tunneling

Inelastic Electron Tunneling Spectroscopy (IETS) is a new technique for measuring the vibrational spectrum of minute quantities of organic compounds. Sensitivity is its key advantage over the conventional techniques of infrared and Raman spectroscopy. This article will first discuss the technique itself: its theoretical basis, selection rules, sensitivity, vibrational mode shifts due to surface interactions and superconductivity, and sample preparation. Then it will discuss applications of the technique to problems in biology, radiation physics, surface physics, and catalysis.     

Inelastic resonant tunneling

A general expression for the resonant contribution to a tunneling current has been obtained and analyzed in the tunneling Hamiltonian approximation. Two types of resonant tunneling structures are considered: structures with a random impurity distribution and double-barrier structures, where the resonant level results from size quantization. The effect of temperature on the current-voltage curves of tunneling structures is discussed. The study of the effect of potential barrier profile on the d ² I/dV ² line shape is of interest for experiments in inelastic tunneling spectroscopy. Various experimental situations where the inelastic component of the tunneling current can become comparable to the elastic one are discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 1151–1155 (June 1998)     

Microwave assisted tunneling

Results obtained from experiments on microwave assisted tunneling are found to be in excellent agreement with the existence of geometrical resonances in the superconducting junction structure.     

Possibility of observing magnetic macroscopic quantum tunneling using a scanning tunneling microscope

A theory describing the detection of magnetic macroscopic quantum tunneling on the basis of current fluctuations in a scanning tunneling microscope is proposed. Zh. éksp. Teor. Fiz. 112, 1011–1020 (September 1997)     

Spectral stability under tunneling

We study the spectral properties of multiple well Schrödinger operators on ⁿ . We give in particular upper bounds on energy shifts due to tunnel effect and localization properties of wave packets. Our methods are based on Agmon type estimates for resolvents in classically forbidden regions and geometric perturbation theory. Our results are valid also for an infinite number of wells, arbitrary spectral type and in non-semi-classical regimes.Laboratoire Propre, Centre National de la Recherche ScientifiquePhymat, Université de Toulon et du Var     

Superconducting tunneling in PdH

Tunneling measurements have been made on superconducting PdH films. The measured2Δ₀/kT_c ratio was 3.80 ± 0.15 meV. Structure was found in the tunneling density of states at an energy of 48 ± 2 meV, approximately the energy of optic phonons in PdH.     

Nanoelectromechanics and single-charge tunneling

The coupling of electronic and mechanical degrees of freedom has important consequences in nanoscale systems, as emphasized in recent theoretical and experimental work. In particular, the electrical properties of composite nanosystems containing elements with quite different abilities to conduct electricity and with different mechanical properties have been found to be strongly affected. Here we briefly review some of our recent work on the nanoelectromechanics of “heteroconducting” and “heteroelastic” Coulomb blockade systems, where single charge tunneling is the dominant conduction mechanism. We examplify nanoelectromechanical effects both in normal and superconducting systems by discussing (i) a self-assembled single-electron tunneling device exhibiting a dynamical instability leading to “shuttling” of electrons by a movable Coulomb dot and (ii) shuttling of Cooper pairs by a movable single-Cooper-pair box.     

Quasi-distribution of tunneling time

Using real time Feynman histories, a quasi-distribution of tunneling time Q(τ) is introduced. For the tunneling time of resident time type, an explicit expression for Q is shown for square barriers. Q becomes oscillatory as the barrier becomes opaque. Some well-known tunneling times fall within the range of τ where Q takes non-negligible values. The formal “average” and the “variance” of the tunneling time are found to be related to known tunneling times. It is thus demonstrated that the quasi-distribution extracts the temporal information about tunneling from real time Feynman histories.