Quenching of phase coherence in quasi-one dimensional ring crystals

The comparison of the single-particle (SP) dynamics between the whisker and ring NbSe$_3$ crystals provides new insight into the phase transition properties in quasi-one-dimensional charge density wave (CDW) systems.Comment: 9 pages, 4 figure

Shot Noise with Interaction Effects in Single Walled Carbon Nanotubes

We have measured shot noise in single walled carbon nanotubes (SWNT) with good contacts at 4.2 K at low frequencies ($f=600 - 850$ MHz). We find a strong modulation of shot noise over the Fabry-Perot pattern; in terms of differential Fano factor the variation ranges over 0.4 - 1.2. The shot noise variation, in combination with differential conductance, is analyzed using two (spin-degenerate) modes with different, energy-dependent transmission coefficients. No power law dependence of shot noise, as expected for Luttinger liquids, was found in our measurements.Comment: 5 pages, 4 figure

Diffusive Josephson junctions made out of multiwalled carbon nanotubes

We have investigated electrical transport in diffusive multiwalled carbon nanotubes (MWNT) contacted using superconducting leads made of Ti/Al/Ti sandwich structure. We measure proximity-induced supercurrents up to Icm = 1.3 nA and find tunability by the gate voltage due to variation of the Thouless energy via the diffusion constant that is controlled by scattering in the MWNT. The modeling of these results by long, diffusive SNS junctions, supplemented with phase diffusion effects is discussed: the agreement between theory and experiments is tested especially on the basis of the temperature dependence of the Josephson coupling energy. In order to prove conclusively that the diffusive model works for MWNT proximity junctions, we propose an improved measurement scheme that is based on the kinetic inductance of superconducting junctions.Peer reviewe

The Mixed State of Charge-Density-Wave in a Ring-Shaped Single Crystals

Charge-density-wave (CDW) phase transition in a ring-shaped crystals, recently synthesized by Tanda et al. [Nature, 417, 397 (2002)], is studied based on a mean-field-approximation of Ginzburg-Landau free energy. It is shown that in a ring-shaped crystals CDW undergoes frustration due to the curvature (bending) of the ring (geometrical frustration) and, thus, forms a mixed state analogous to what a type-II superconductor forms under a magnetic field. We discuss the nature of the phase transition in the ring-CDW in relation to recent experiments.Comment: 6 pages, 4 figure

Drift-Kinetic Modeling of Particle Acceleration and Transport in Solar Flares

Based on the drift-kinetic theory, we develop a model for particle acceleration and transport in solar flares. The model describes the evolution of the particle distribution function by means of a numerical simulation of the drift-kinetic Vlasov equation, which allows us to directly compare simulation results with observations within an actual parameter range of the solar corona. Using this model, we investigate the time evolution of the electron distribution in a flaring region. The simulation identifies two dominant mechanisms of electron acceleration. One is the betatron acceleration at the top of closed loops, which enhances the electron velocity perpendicular to the magnetic field line. The other is the inertia drift acceleration in open magnetic field lines, which produces antisunward electrons. The resulting velocity space distribution significantly deviates from an isotropic distribution. The former acceleration can be a generation mechanism of electrons that radiate loop-top nonthermal emissions, and the latter be of escaping electrons from the Sun that should be observed by in-situ measurements in interplanetary space and resulting radio bursts through plasma instabilities.Comment: 32 Pages, 11 figures, accepted by Ap

Measurements of shot noise in single walled carbon nanotubes

We have measured shot noise in single walled carbon nanotubes (SWNT) at 4.2K over frequencies f = 600 – 850 MHz. Here we report results obtained on shot noise without DC bias by applying an AC modulation at ω0 and recording the noise variation at 2ω0: the Fano factor is obtained by extrapolating down to zero excitation amplitude. We also discuss the applicability of this method in samples which have strongly non‐linear IV characteristics like carbon nanotubes. The obtained results are compared with regular differential noise measurements where both DC and AC bias are employed.Peer reviewe

Formation Process of a Light Bridge Revealed with the Hinode Solar Optical Telescope

The Solar Optical Telescope (SOT) aboard HINODE successfully and continuously observed a formation process of a light bridge in a matured sunspot of the NOAA active region 10923 for several days with high spatial resolution. During its formation, many umbral dots were observed emerging from the leading edges of penumbral filaments, and intruding into the umbra rapidly. The precursor of the light bridge formation was also identified as the relatively slow inward motion of the umbral dots which emerged not near the penumbra, but inside the umbra. The spectro-polarimeter on SOT provided physical conditions in the photosphere around the umbral dots and the light bridges. We found the light bridges and the umbral dots had significantly weaker magnetic fields associated with upflows relative to the core of the umbra, which implies that there was hot gas with weak field strength penetrating from subphotosphere to near the visible surface inside those structures. There needs to be a mechanism to drive the inward motion of the hot gas along the light bridges. We suggest that the emergence and the inward motion are triggered by a buoyant penumbral flux tube as well as the subphotospheric flow crossing the sunspot.Comment: 8 pages, 6 figures, accepted in the PASJ Hinode special issu