Madoka Tokumoto

Superconductivity with the Onset at 8 K in the Organic Conductor β-(BEDT-TTF)2I3 under Pressure

We report the superconductivity with the onset temperature as high as 8 K in the organic conductor of β-(BEDT-TTF) 2 I 3 , bis-ethylenedithio otetrathiofulvalene-triiodide. The increased superconducting transition temperature was achieved by an application of a soft pressure, i.e. 1.3 kb. High value of the upper critical field, H c2 was observed. ( H c2 >13 kOe at 1.5 K along the c * -axis.)

Ultrashort pulse-generation by saturable absorber mirrors based on polymer-embedded carbon nanotubes.

We demonstrate passive mode locking of solid-state lasers by saturable absorbers based on carbon nanotubes (CNT). These novel absorbers are fabricated by spin-coating a polymer doped with CNTs onto commercial dielectric laser-mirrors. We obtain broadband artificial saturable absorber mirrors with ultrafast recovery times without the use of epitaxial growth techniques and the well-established spin-coating process allows the fabrication of devices based on a large variety of substrate materials. First results on passive mode locking of Nd:glass and Er/Yb:glass lasers are discussed. In the case of Er/Yb:glass we report the to our knowledge shortest pulse generated in a self-starting configuration based on Er/Yb:bulk-glass: 68 fs (45 fs Fourier-limit) at 1570 nm wavelength at a pulse-repetition rate of 85 MHz.

Sub-200-fs pulsed erbium-doped fiber laser using a carbon nanotube-polyvinylalcohol mode locker

We study the difference in mode-locked operations of different saturable absorber films made of single wall carbon nanotube-polyvinylalcohol nanocomposite. The films have different nanotube concentrations and thicknesses. For the study, a mode-locked erbium-doped fiber laser in a ring cavity configuration was constructed by setting the films in a microgap between a pair of fiber end facets. With the optimum film among those we have tested, the shortest pulses with a width of 178fs were achieved at 1.56μm with a repetition rate of 22.8MHz and an average power of 1.55mW.

Simple synthesis of three primary colour nanoparticle inks of Prussian blue and its analogues

Historic Prussian blue (PB) pigment is easily obtained as an insoluble precipitate in quantitative yield from an aqueous mixture of Fe3+ and [FeII(CN)6]4? (Fe2+ and [FeIII(CN)6]3?). It has been found that the PB pigment is inherently an agglomerate of 10?20?nm nanoparticles, based on powder x-ray diffraction (XRD) line broadenings and transmission electron microscopy (TEM) images. The PB pigment has been revived as both organic-solvent-soluble and water-soluble nanoparticle inks. Through crystal surface modification with aliphatic amines, the nanoparticles are stably dispersed from the insoluble agglomerate into usual organic solvents to afford a transparent blue solution. Identical modification with [Fe(CN)6]4? yields water-soluble PB nanoparticles. A similar ink preparation is applicable to Ni-PBA and Co-PBA (nickel and cobalt hexacyanoferrates). The PB (blue), Ni-PBA (yellow), and Co-PBA (red) nanoparticles function as three primary colour inks.

Superconductivity in an Organic Insulator at Very High Magnetic Fields

We investigate by electrical transport the field-induced superconducting state (FISC) in the organic conductor lambda-(BETS)2FeCl4. Below 4 K, antiferromagnetic-insulator, metallic, and eventually superconducting (FISC) ground states are observed with increasing in-plane magnetic field. The FISC state survives between 18 and 41 T and can be interpreted in terms of the Jaccarino-Peter effect, where the external magnetic field compensates the exchange field of aligned Fe3+ ions. We further argue that the Fe3+ moments are essential to stabilize the resulting singlet, two-dimensional superconducting state.

Transport properties of organic conductor (BEDT-TTF)2KHg(SCN)4: I. Resistance and magnetoresistance anomaly

Abstract The electrical resistance of the single crystalline organic salt (BEDT-TTF) 2 KHg(SCN) 4 has been measured at temperatures down to 0.5 K and under magnetic fields up to 13 T. The zero-field resistance decreases almost monotonously with decreasing temperature down to 9–10 K and then exhibits a step-like anomaly accompanying the 30–40% resistance drop around below T a =8 K. Under fields perpendicular to the conducting a-c plane, the resistance below T a is so enhanced that an upturn in the temperature-dependent resistance appears and the resistance, for example, at 13 T and 0.5 K, becomes higher by a factor of 12 than the resistance at T a and H =13 T. This anomalous magnetoresistance is never observed under fields precisely aligned parallel to the a-c plane. The dc magnetic susceptibility shows a broad maximum at T a , which seems to be an evidence that weak anti-ferromagnetic correlations like spin-density-wave ordering takes place among p (п) electrons itinerating in the metallic states.

Carbon Nanotube-Poly(vinylalcohol) Nanocomposite Film Devices: Applications for Femtosecond Fiber Laser Mode Lockers and Optical Amplifier Noise Suppressors

We fabricated single-wall carbon nanotube (SWNT)/poly(vinylalcohol) (PVA) nanocomposite freestanding films and examined their application in devices in which the saturable absorption of SWNTs at near-infrared optical telecommunication wavelengths can be utilized. In a passively mode-locked fiber laser, we integrated a 30-µm-thick SWNT/PVA film into a fiber connection adaptor with the film sandwiched by a pair of fiber ferrules. A ring fiber laser with a SWNT/PVA saturable absorber was operated very easily in the mode-locked short-pulse mode with a pulse width of about 500 fs. Reproducible stable device performance was confirmed. In examining noise suppression for optical amplifiers, mixed light of semiconductor amplified spontaneous emission (ASE) source and 370 fs laser pulses was passed through a 100-µm-thick SWNT/PVA film. The transmission loss of the femtosecond pulse light was smaller than that of the ASE light. This proved that the SWNT/PVA film has the ability to suppress ASE noise.

Selective etching of metallic single-wall carbon nanotubes with hydrogen plasma

We present Raman scattering and scanning tunnelling microscopy (STM) measurements on hydrogen plasma etched single-wall carbon nanotubes (SWNTs). Interestingly, both the STM and Raman spectroscopy show that the metallic SWNTs are dramatically altered and highly defected by the plasma treatment. In addition, structural characterizations show that metal catalysts are detached from the ends of the SWNT bundles. For semiconducting SWNTs we observe no feature of defects or etching along the nanotubes. Raman spectra in the radial breathing mode region of plasma-treated SWNT material show that most of the tubes are semiconducting. These results show that hydrogen plasma treatment favours etching of metallic nanotubes over semiconducting ones and therefore could be used to tailor the electronic properties of SWNT raw materials.

Atomic structure and electronic properties of single-wall carbon nanotubes probed by scanning tunneling microscope at room temperature

A detailed three-dimensional structural analysis of single-walled carbon nanotubes was carried out using a scanning tunneling microscope (STM) operated at room temperature in ambient conditions. On a microscopic scale, the images show tubes condensed in ropes as well as tubes which are separated from each other. For a single-wall nanotube rope, the outer portion is composed of highly oriented nanotubes with nearly uniform diameter and chirality. On separated nanotubes, atomically resolved images show variable chirality ranges between 0°–30°, and variable diameter (1–3 nm), with no one type dominant. From STM and scanning tunneling spectroscopy measurements we confirmed the correlation between chirality and the electronic properties, namely the tuning from metallic to semiconducting. We also observed a rectifying behavior correlated with the chiral angle of 25°, an important observation for nanodevices application.

How to make superconducting-anisotropy least in high-Tc cuprate superconductors

Abstract The guiding principles to reduce superconducting-anisotropy were derived for high-T c cuprate superconductors. Based on the principles, we have attained the least superconducting-anisotropy γ=1.6 for a Cu-based CuBa 2 Ca 3 Cu 4 O 12−y (Cu-1234) superconductor. Further lower superconducting-anisotropy has been proposed for Cu-1245 (γ=1.3) and Cu-1256 (γ≌1.0) Cu-based superconductors.