Tunneling spectroscopy of a two-dimensionally periodic electron system

The tunneling current between an electron gas with a periodic potential in two dimensions and a plain two-dimensional electron system (2DES) has been studied. The strength of the periodic potential, the subband energy of the plain 2DES, and an applied in-plane magnetic field were varied, mapping the Fourier transform of the periodic wave function. Periodic peaks were observed and explained by translations in the reciprocal lattice. When the potential was strongly modulated to form an array of antidots, commensurability peaks were seen in lateral transport, but, as expected, not in tunneling.     

Tunneling spectroscopy of electron space charge layers on (111)-Si

MgSiO₂Si tunnel junctions were prepared on nondegenerate substrates in a planar structure. By suitable technology-steps a low-resistance connection between the diffused drain contact and an electron enhancement channel, which was generated by the work function difference of the electrodes and charged defects in the barrier region, can be realized; therefore low-temperature measurements of the current-voltage characteristic and its derivatives were possible. In the $\text{d}{}^2\text{I}\text{dU}{}^2$ vs. U-traces various structures have been observed, which were caused by band edge effects of numerous surface subbands, by phonon-assisted tunneling and by a zero-bias anomaly. At nearly constant surface charge density the energy separation of the subbands and its dependence on depletion charge density, varied by the application of a substrate bias, has been measured. Because of the direct reading of the subband energies relative to the Fermi-level the surface density could be estimated.     

Spin current in an electron waveguide tunnel-coupled to a topological insulator

We show that electron tunneling from edge states in a two-dimensional topological insulator into a parallel electron waveguide leads to the appearance of spin-polarized current in the waveguide. The spin polarization P can be very close to unity and the electron current passing through the tunnel contact splits in the waveguide into two branches flowing from the contact. The polarization essentially depends on the electron scattering by the contact and the electron-electron interaction in the one-dimensional edge states. The electron-electron interaction is treated within the Luttinger liquid model. The main effect of the interaction stems from the renormalization of the electron velocity, due to which the polarization increases with the interaction strength. Electron scattering by the contact leads to a decrease in P. A specific effect occurs when the bottom of the subbands in the waveguide crosses the Dirac point of the spectrum of edge states when changing the voltage or chemical potential. This leads to changing the direction of the spin current.     

Tunneling spectroscopy of voltage tunable quantum wires

Resonant tunneling spectroscopy is used to investigate the tuning range for the one-dimensional subband spacing of side-gated quantum wires. We introduce a simplified selective depletion scheme for the implementation of a resonant tunneling device. From the analysis of the differential tunneling conductance obtained for a single-wire device we conclude that the energetic spacing for the one-dimensional subbands can be varied from effectively 0 to about 6 meV. Measurements in magnetic fields directed parallel and perpendicular to the tunnel current confirm the one-dimensional nature of the tunneling processes as well as the order of magnitude of the subband spacing by comparison of the tunneling characteristics with a model calculation that assumes a parabolic confinement.     

Wakefield radiation generated by an electron bunch in a rectangular dielectric waveguide

Vavilov-Cerenkov radiation generated by a relativistic electron bunch in a rectangular waveguide with a transverse-inhomogeneous dielectric filling is analyzed. A method is proposed for constructing an orthogonal basis of the transverse operator, which can be subsequently used for determining the wakefield of the relativistic bunch moving parallel to the waveguide axis. The dispersion equation for the structure is derived and the expressions for the wake field produced by such a bunch are obtained. The formalism described here forms the basis for calculating parameters of the accelerating structure for generator bunches of the Argonne Wakefield Accelerator (AWA) at the Argonne National Laboratory and the FACET complex of the SLAC accelerator. It is shown that using such structures, accelerating field gradients higher than 150 MV/m can be generated at frequencies 20?C35 GHz and exceeding 1 GeV/m in the frequency range ??1 THz.     

Tunneling spectroscopy as a probe of adsorbate-surface interactions

Tunneling spectroscopy is a sensitive probe of two classes of adsorbate-surface interactions: interactions of the adsorbate with the substrate on which it is adsorbed and adsorbate interactions with the top metal electrode that is evaporated on top of it. The talk by Professor Hipps focuses on the first of these classes. This talk focuses on the second. In general, the interaction of the adsorbed molecules with the top metal electrode produces a down-shift in the vibrational mode position ranging in size from 0.1% to 10% depending on the dipole derivative of the mode and the type of top metal electrode.     

Superlight source of radiation with a waveguide used for bunching an electron beam

A scheme of a generator of electromagnetic-wave radiation is proposed in which a radiating region moves along a radiator with a velocity greater than the velocity of light in vacuum. The superlight motion of the generating region leads to the situation in which the resulting radiation has the properties of Vavilov-Cherenkov radiation. The electron beam of a superlight source is formed while the particles travel across a waveguide along which an electromagnetic wave propagates. The construction of the generator makes it possible to vary the velocity of the radiating region, the radiation pattern, and the radiation beamwidth. Calculations are performed that allow one to evaluate the parameters of the generator and the characteristics of radiation.     

Infrared wave interaction with an electron in the rectangular and circular plasma waveguide

In this article, the effect of the electron collision frequency with background ions on TM mode field components, the trajectory, and the electron energy gain in interaction infrared radiation with collisional plasma is studied. The field components of the TM mode in the rectangular and circular collisional plasma waveguides are obtained. The deflection angle and acceleration gradient of an electron in the fields associated with a transverse magnetic (TM) wave propagating inside a plasma waveguide for TM mode is studied. The relativistic momentum and energy equations for an electron are solved, which was injected initially along the propagation direction of the infrared. The results for collisionless and collisional plasma are graphically represented. Finally, the results for rectangular and circular waveguides are compared.     

Tunneling spectroscopy and vortex imaging in boron-doped diamond

We present the first scanning tunneling spectroscopy study of single-crystalline boron-doped diamond. The measurements were performed below 100 mK with a low temperature scanning tunneling microscope. The tunneling density of states displays a clear superconducting gap. The temperature evolution of the order parameter follows the weak-coupling BCS law with Delta(0)/kBTc approximately 1.74. Vortex imaging at low magnetic field also reveals localized states inside the vortex core that are unexpected for such a dirty superconductor.