Variable range hopping in Si:P at very low temperature

The resistivity of doped semiconductor Si: P in the intermidiate concentration range was measured in low temperature region down to 10 mK. In the lowest temperatures Mott's formula for the variable range hopping is shown to be not applicable and T^-n-like temperature dependence of resistivity is confirmed. The Importance of the level correlation in the random system is discussed.     

Anomalous magnetoresistance in heavily antimony doped germanium

Anomalous magnetoresistance in heavily antimony doped germanium is studied down to 5 mK. The experimental results is reasonably interpreted within a framework of s-d interaction with a negative exchange constant. Electrons localized in a sense of Anderson are suggested to play a role of d electrons when Coulomb correlation is introduced.     

Tunneling spectroscopy of isolated gold clusters grown on thiol/dithiol mixed self-assembled monolayers

We report a scanning tunneling spectroscopy study on the size-tunable isolated gold nanoclusters grown on thiol/dithiol mixed self-assembled monolayers (SAMs) where the effect of neighboring clusters are practically excluded. The structure forms double tunnel junction system in which the spectra exhibit Coulomb staircases. With increasing cluster size the standard deviation of the offset charge distribution for clusters increases, accompanied with the increase of total capacitance. The results are qualitatively same with the previous ones where clusters are densely grown on the substrate, indicating that this behavior is an intrinsic property for the double tunnel junction structures of tip/vacuum/single cluster/SAMs/Au(1 1 1) systems.     

Superconductor-insulator transition in a two-dimensional array of resistively shunted small josephson junctions

Using a scattering technique based on a parametrized linear combination of atomic orbitals Hamiltonian, we calculate the ballistic quantum conductance of multiwall carbon nanotubes. We find that interwall interactions not only block some of the quantum conductance channels, but also redistribute the current nonuniformly over individual tubes across the structure. Our results provide a natural explanation for the unexpected integer and noninteger conductance values reported for multiwall nanotubes by Stefan Frank et al. [Stefan Frank et al., Science 280, 1744 (1998)].     

Experimental evidence for giant vortex states in a mesoscopic superconducting disk

The response of a mesoscopic superconducting disk to perpendicular magnetic fields is studied by using the multiple-small-tunnel-junction method, in which transport properties of several small tunnel junctions attached to the disk are measured simultaneously. This allows us to make the first experimental distinction between the giant vortex states and multivortex states. Moreover, we experimentally find a magnetic-field induced rearrangement and combination of vortices. The experimental results are well reproduced in numerical results based on the nonlinear Ginzburg-Landau theory.     

Gate-voltage dependence of zero-bias anomalies in multiwall carbon nanotubes

Temperature dependence of zero-bias conductance of the vanadium (V)/multiwall carbon nanotube (MWNT)/V structure is studied. As temperature is reduced, the conductance decreases with a functional form consistent with a power law. For the first time, we find that the exponent depends significantly on gate voltage. This exponent dependence cannot be explained by Luttinger-liquid theory for ballistic MWNTs. We interpret the obtained results within the framework of the nonconventional Coulomb blockade theory for strongly disordered MWNTs.     

Experimental distinction between giant vortex and multivortex states in mesoscopic superconducting squares

We study the distinction between giant vortex states and multivortex states in a thin mesoscopic superconducting square by using the temperature dependence of the vortex expulsion fields. We find that the results agree well with those obtained from the multiple-small-tunnel-junction method, indicating that the distinction by the temperature dependence of the vortex expulsion fields is applicable to superconducting squares.     

Simple and controlled fabrication of nanoscale gaps using double-angle evaporation

A simple and controlled method for fabricating nanometer-spaced electrodes is presented. This method uses electron-beam lithography followed by double-angle evaporation of thin metallic films. By simply changing the film thickness, one can adjust the separation of the electrodes. In this method, error is caused mainly by the granularity of the deposited metals. We have observed the Coulomb blockade effect of 20 nm Au colloidal particles captured in a gap fabricated using this method.     

Molecular effect of Al K α X-ray yields from aluminum oxide films for H+ and H+2 ion bombardments

Al Kα X-ray spectra for equi-velocity H⁺ and H⁺₂ ions of ? 0.9 MeV/amu incident on thin aluminum oxide films with thickness 100 and 300 Å were observed. The intensity ratio of the KL¹ satellite line to the KL⁰ main one for H⁺₂ incident on the films of thickness 100 and 300 Å was about 10% and 4% larger than that for incident H⁺, respectively.