New carbon-based superconductors are synthesized by intercalating metal atoms into the solid-phase hydrocarbons picene and coronene. The highest reported superconducting transition temperature, T(c), of a hydrocarbon superconductor is 18 K for K(3)picene. The physics and chemistry of the hydrocarbon superconductors are extensively described for A(x)picene (A: alkali and alkali earth-metal atoms) for x = 0-5. The theoretical picture of their electronic structure is also reviewed. Future prospects for hydrocarbon superconductors are discussed from the viewpoint of combining electronics with condensed-matter physics: modification of the physical properties of hydrocarbon solids is explored by building them into a field-effect transistor. The features of other carbon-based superconductors are compared to clarify the nature of hydrocarbon superconductors.

The competition between electron localization and de-localization in Mott insulatorsunderpins the physics of strongly-correlated electron systems. Photo-excitation, which redistributes charge between sites, can control this many-body process on the ultrafast In Mott insulators, conductivity at low energies is prevented by repulsion among electrons.This state is fundamentally different from that of conventional band insulators, in which Bragg scattering from the lattice opens gaps in the single particle density of states. The electronic structure of Mott insulators is, therefore, sensitive to doping. Photo-excitation, in analogy to static doping, can trigger large changes in the macroscopic properties viii .However, the coherent physics driving these transitions has not been fully observed because the many-body electronic dynamics are determined by hopping and correlation processes that only persist for a few femtoseconds.We report measurements of coherent many-body dynamics with ultrafast optical spectroscopy in the one-dimensional Mott insulator ET-F2TCNQ. Several factors make this possible: ET-F2TCNQ has a narrow bandwidth (~ 100 meV), which corresponds to hopping times of tens of femtoseconds; the material has a weak electron-lattice interaction; we use a novel optical device producing pulses of 9 fs at the 1.7 m Mott gap; we study this physics in a one-dimensional system, allowing the evolution of the many-body wavefunction to be calculated and compared with experimental data. The characteristics of this new peak are time dependent, as visualized in Fig. 2c, where we have normalized the reflectivity at each time step. Two contours are shown in Fig. 2c. On the blue side, a prompt red-shift and recovery of the resonance is observed, whereas the red side shows a longer-lived component, containing a damped oscillatory response at 25 THz. StaticRaman data on ET-F2TCNQ does not show any equivalent features, strongly suggesting that the oscillation is not due to coherent phonons, but of an electronic origin xiv .To investigate such dynamics, we used a one-dimensional Mott-Hubbard Hamiltonian for a half-filled chain, with N = 10 sites, with electron hopping, t, and onsite and nearest neighbourCoulomb repulsion U and V, where, c †l, and cl, are the creation and annihilation operators for an electron at site l with spin , nl, is the number operatorand nl = nl, + nl,. We described the initial state, where  represents a many-body wavefunction with one electron per site and total spin-vector . This reflects the fact that, at room temperature, charges are localized, but posses no magnetic ordering.We calculate the static optical conductivity (see methods section) to find values of U, V and t that provide the best fit to the experimental results. The best fit, shown in Fig. 3c (t = -200 fs), gave U = 820 meV, V = 100 meV and t = 50 meV. It was not possible to fit the optical conductivity using U and t alone and inter-site correlation energy, V, was needed xv .These static parameters were used to fit to the...

Charge dynamics in a one-dimensional (1D) Mott insulator was investigated by fs pump-probe reflection spectroscopy on an organic charge-transfer compound, bis(ethylenedithio)tetrathiafulvalene-difluorotetracyanoquinodimethane (ET-F2TCNQ). The analyses of the transient reflectivity changes demonstrate that low-energy spectral weight induced by photocarrier doping is concentrated on a Drude component being independent of the doping density, and midgap state is never formed. Such phenomena can be explained by the concept of spin-charge separation characteristic of 1D correlated electron systems.

We report electronic structure and physical properties of metal-doped picene as well as selective synthesis of the phase that exhibits 18 K superconducting transition. First, Raman scattering is used to characterize the number of electrons 2 transferred from the dopants to picene molecules, where a softening of Raman scattering peaks enables us to determine the number of transferred electrons.From this we have identified that three electrons are transferred to each picene molecule in the superconducting doped picene solids. Second, we report pressure dependence of T c in 7 K and 18 K phases of K 3 picene. The 7 K phase shows a negative pressure-dependence, while the 18 K phase exhibits a positive pressure-dependence which cannot be understood with a simple phonon mechanism of BCS superconductivity. Third, we report a new synthesis method for superconducting K 3 picene by a solution process with monomethylamine, CH 3 NH 2 . This method enables us to prepare selectively the K 3 picene sample exhibiting 18 K superconducting transition. The method for preparing K 3 picene with T c = 18 K found here may facilitate clarification of the mechanism of superconductivity.Corresponding author: Takashi Kambe, kambe@cc.okayama-u.ac.jp & Yoshihiro Kubozono, kubozono@cc.okayama-u.ac.jp 3 I. IntroductionRecently a new class of organic superconductors has been discovered in aromatic systems. They are solids of hydrocarbons that include picene, coronene, phenanthrene and 1,2:8,9-dibenzopentacene, 1-6 doped with metal atoms. Namely, the superconductivity was first discovered in potassium-doped picene, K 3 picene, which showed two different superconducting transition temperatures, one with T c = 7 K and the other as high as 18 K. 1 This has been followed by other studies, and the highest T c among these hydrocarbon superconductors to date attains 33 K observed in K 3.45 dibenzopentacene, 6 whose T c is much higher than the highest T c (14.2 K at 8.2 GPa 7 in β'-(BEDT-TTF) 2 ICl 2 ) in charge-transfer organic superconductors. Thus the hydrocarbon superconductors are very attractive from viewpoints of development of new high-T c superconductors as well as fundamental physics of superconductivity.Theoretical calculations for picene superconductors were also achieved, which suggests that the electron-phonon coupling is strong, 8,9 the conduction band comprises four bands arising from two LUMO orbitals, 10 and that strong hybridization between the dopants and molecules invalidates a rigid-band picture. 10The departure from the rigid-band picture was experimentally evidenced by photoemission spectroscopy. 11 This photoemission study clearly showed a metallic ground state for potassium-doped picene films. Our recent resistivity data also indicate a metallic behavior for the K 3 picene phase. 12 Further, a Pauli paramagnetic susceptibility was observed for a K 3 picene bulk sample. 1 These results support a metallic ground state for K 3 picene.The T c for the solid K 3 picene was found to be either 7 or 18 K, 1,2 while the T c of K 3 phenant...

We established tobacco tumour cell lines from crown galls induced by Agrobacterium. Restriction fragments containing T-DNA/plant DNA junctions were cloned from one of the cell lines, which has a single copy of the T-DNA in a unique region of its genome. We also isolated a DNA fragment that contained the integration target site from nontransformed tobacco cells. Nucleotide sequence analyses showed that the right and left breakpoints of the T-DNA mapped ca. 7.3 kb internal to the right 25 bp border and ca. 350 bp internal to the left border respectively. When the nucleotide sequences around these breakpoints were compared with the sequence of the target, significant homology was seen between the region adjacent to the integration target site and both external regions of the T-DNA breakpoints. In addition, a short stretch of plant DNA in the vicinity of the integration site was deleted. This deletion seems to have been promoted by homologous recombination between short repeated sequences that were present on both sides of the deleted stretch. Minor rearrangements, which included base substitutions, insertions and deletions, also took place around the integration site in the plant DNA. These results, together with previously reported results showing that in some cases sequences homologous to those in T-DNA are present in plant DNA regions adjacent to left recombinational junctions, indicate that sequence homology between the incoming T-DNA and the plant chromosomal DNA has an important function in T-DNA integration.(ABSTRACT TRUNCATED AT 250 WORDS)