Local current injection into mesoscopic superconductors for the manipulation of quantum states

We perform strategic current injection in a small mesoscopic superconductor and control the (non)equilibrium quantum states in an applied homogeneous magnetic field. In doing so, we realize a current-driven splitting of multi-quanta vortices, current-induced transitions between states with different angular momenta, and current-controlled switching between otherwise degenerate quantum states. These fundamental phenomena form the basis for discussed electronic and logic applications, and are confirmed in both theoretical simulations and multiple-small-tunnel-junction transport measurements.Comment: To appear in Physical Review Letter

First Results from Dark Matter Search Experiment in the Nokogiriyama Underground Cell

An experiment to search for hypothetical particle dark matter using cryogenic thermal detector, or bolometer is ongoing. The bolometer consists of eight pieces of 21 g LiF absorbers and sensitive NTD germanium thermistors attached to them and is installed in the Nokogiriyama underground cell which is a shallow depth site ($\sim 15$ m w.e.). We report on the results from the first running for about ten days using this arrayed bolometer system together with appropriate shieldings and muon veto counters. From the obtained energy spectra the exclusion limits for the cross section of the elastic neutralino-proton scattering are derived under commonly accepted astrophysical assumptions. The sensitivity for the light neutralino with a mass below 5 GeV is improved by this work.Comment: 8 pages, Revtex, 4 figure

Magetoresistance of RuO_2-based resistance thermometers below 0.3 K

We have determined the magnetoresistance of RuO_2-based resistors (Scientific Instruments RO-600) between 0.05 K and 0.3 K in magnetic fields up to 8 T. The magnetoresistance is negative around 0.5 T and then becomes positive at larger fields. The magnitude of the negative magnetoresistance increases rapidly as the temperature is lowered, while that of the positive magnetoresistance has smaller temperature dependence. We have also examined the temperature dependence of the resistance below 50 mK in zero magnetic field. It is described in the context of variable-range-hopping conduction down to 15 mK. Hence, the resistors can be used as thermometers down to at least 15 mK.Comment: 6 pages with 7 embedded figures. Published version (very minor changes

First results from dark matter search experiment with LiF bolometer at Kamioka Underground Laboratory

Tokyo group has performed first underground dark matter search experiment in 2001 through 2002 at Kamioka Observatory(2700m.w.e). The detector is eight LiF bolometers with total mass 168g aiming for the direct detection of WIMPs via spin-dependent interaction. With a total exposure of 4.1 kg days, we derived the limits in the a_p-a_n (WIMP-nucleon couplings) plane and excluded a large part of the parameter space allowed by the UKDMC experiment.Comment: 15 pages, 5 figure

Introducing Nonuniform Strain to Graphene Using Dielectric Nanopillars

A method for inducing nonuniform strain in graphene films is developed. Pillars made of a dielectric material (electron beam resist) are placed between graphene and the substrate, and graphene sections between pillars are attached to the substrate. The strength and spatial pattern of the strain can be controlled by the size and separation of the pillars. Application of strain is confirmed by Raman spectroscopy as well as from scanning electron microscopy (SEM) images. From SEM images, the maximum stretch of the graphene film reaches about 20%. This technique can be applied to the formation of band gaps in graphene.Comment: Appl. Phys. Express, in pres

Influence of electronic correlations on the frequency-dependent hopping transport in Si:P

At low energy scales charge transport in the insulating Si:P is dominated by activated hopping between the localized donor electron states. Thus, theoretical models for a disordered system with electron-electron interaction are appropriate to interpret the electric conductivity spectra. With a newly developed technique we have measured the complex broadband microwave conductivity of Si:P from 100 MHz to 5 GHz in a broad range of phosphorus concentration $n/n_c$ from 0.56 to 0.95 relative to the critical value $n_c=3.5\times 10^{18}$ cm$^{-3}$ corresponding to the metal-insulator transition driven by doping. At our base temperature of $T =1.1$ K the samples are in the zero-phonon regime where they show a super-linear frequency dependence of the conductivity indicating the influence of the Coulomb gap in the density of the impurity states. At higher doping $n\to n_c$, an abrupt drop in the conductivity power law \sig(\omega)\sim\omega^\alpha is observed. The dielectric function \eps increases upon doping following a power law in ($1-n/n_c$). Dynamic response at elevated temperatures has also been investigated.Comment: 5 pages, 7 figures, conference "Transport in Interacting Disordered Systems" Marburg, August 6 - 10, 200