From the Berkovits formulation to the Witten formulation in open superstring field theory

The Berkovits formulation of open superstring field theory is based on the large Hilbert space of the superconformal ghost sector. We discuss its relation to the Witten formulation based on the small Hilbert space. We introduce a one-parameter family of conditions for partial gauge fixing of the Berkovits formulation such that the cubic interaction of the theory under the partial gauge fixing reduces to that of the Witten formulation in a singular limit. The local picture-changing operator at the open-string midpoint in the Witten formulation is regularized in our approach, and the divergence in on-shell four-point amplitudes coming from collision of picture-changing operators is resolved. The quartic interaction inherited from the Berkovits formulation plays a role of adjusting different behaviors of the picture-changing operators in the $s$ channel and in the $t$ channel of Feynman diagrams with two cubic vertices, and correct amplitudes in the world-sheet theory are reproduced. While gauge invariance at the second order in the coupling constant is obscured in the Witten formulation by collision of picture-changing operators, it is well defined in our approach and is recovered by including the quartic interaction inherited from the Berkovits formulation.Comment: 50 pages, 2 figures; v2: references added, minor changes, version published in JHE

Photophysics and Inverted Solvatochromism of 7,7,8,8-Tetracyanoquinodimethane (TCNQ)

We report the absorption, fluorescence, and Raman spectroscopy of 7,7,8,8- tetracyanoquinodimethane (TCNQ) in a variety of solvents. The fluorescence quantum yields (QYs) of linear alkane solutions are similar to one another, but QY is shown to acutely decrease in other solvents with increasing polarities. The slope of the solvatochromic plot of absorption maxima is inverted from negative to positive with an increase in solvent polarity. A significant change in the frequency of carbon-carbon double bond stretching modes is not observed in Raman spectra of TCNQ in different solvents. The molar absorption coefficient is determined to calculate the oscillator strength of the absorption band. The radiative decay rate constant calculated from the oscillator strength is approximately ten times larger than that elucidated from the fluorescence lifetime and QY. These spectroscopic parameters reveal that the relaxation occurs from a Franck-Condon excited state to a distinct fluorescence emissive state with a smaller transition dipole moment

Molecular-based light-activated thyristor

A photoinduced electrical conductivity switching is observed in the molecular conductor of alpha-[bis(ethylenedithio)tetrathiafulvalene](2)I-3 at different temperatures with different irradiation light intensities. The threshold voltage for the differential-negative-resistance effect appearing in the current-voltage characteristic curve decreases and increases, respectively, as the light intensity is increased and as the temperature decreases below the insulator-metal phase transition. The potential application of molecular conductor in bidirectional light-activated thyristor devices is demonstrated. (c) 2007 American Institute of Physics

Reversible photoswitching behavior in bulk resistance and in color of polycrystalline AgI at room temperature

A photoinduced reversible change in bulk resistance of polycrystalline AgI is observed at room temperature. The original yellow color of the sample changes to dark brown with UV (308 nm) photoirradiation, associated with the small decrease in the bulk resistance. A reversible switching of color between dark brown and yellow is observed by alternative UV-visible photoirradiation, associated with a switching between high and low resistance states. The observed reversible photoswitching is interpreted in terms of the photoinduced reversible change in the beta-gamma-polytype stacking structure of the polycrystalline AgI

Fluorescence enhancement induced by quadratic electric-field effects on dynamics of singlet exciton in poly(3-hexylthiophene) dispersed in poly(methyl methacrylate)

The dynamics of the exciton generated by photoexcitation of regioregular poly(3-hexylthiophene) (P3HT) polymer dispersed into a poly(methyl methacrylate) (PMMA) matrix has been examined by using electro-photoluminescence (E-PL) spectroscopy, where electric field effects on photoluminescence (PL) spectra have been measured. The quadratic electric-field effect have been investigated by using the modulation technique, with which the field-induced change in PL intensity synchronized at the second harmonic of a modulation frequency of the applied electric fields was monitored. Absorption and PL spectra are indicative of the formation both of the ordered crystalline aggregates and of the amorphous regions of P3HT polymer chains. Although previous studies of the electric field effects on π-conjugated polymers showed, in general, that the PL intensity was decreased by electric fields, we report that the PL intensity of P3HT increases and the PL lifetime becomes longer, as the quadratic electric-field effect. The magnitude of the change in PL intensity was quantitatively explained in terms of the field-induced decrease in the nonradiative decay rate constants of exciton. We conjecture that a delayed PL which originates from the recombination of the charge carriers is enhanced in the presence of electric fields. It is also implied that the rate constant of the downhill relaxation process of the exciton, which originates from the relaxation in distributed energy levels due to inherent energetic disorder in P3HT aggregates, becomes smaller in the presence of electric fields. The radiative decay rate constant and PL quantum yield of P3HT dissolved in solution, which are evaluated from the molar extinction coefficient and the PL lifetime, are compared with the ones of P3HT dispersed in a PMMA matrix

New aspect of photophysics of 7,7,8,8-tetracyanoquinodimethane and its solvated complexes: intra- vs. inter-molecular charge-transfer

We performed laser-induced fluorescence (LIF) spectroscopy of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and its solvated complexes with acetonitrile (ACN) and benzene (Bz), under the jet-cooled gas-phase condition. We also carried out fluorescence and its time profile measurements in TCNQ/Bz/hexane solution to compare with the gas-phase results. The LIF excitation spectrum of the S-1 (pi pi*)-S-0 electronic transition of TCNQ monomer exhibited unusual vibronic structure with the maximum intensity at similar to 3000 cm(-1) above the band origin. In addition, the fluorescence lifetime is more than 100 times longer than that in hexane solution with most of the bands showing double exponential decay. The unusual feature of the vibronic bands is intrinsic and not due to the presence of other species, as confirmed by UV-UV hole-burning (HB) spectroscopy. These unusual features of S-1 are thought to be due to the coupling with the S-2 state, where S-2 was revealed to have intramolecular charge-transfer (ICT) character. The S-1-S-0 transition of the TCNQ-ACN complex exhibited sharp vibronic bands which are red-shifted by 120 cm(-1) from those of the monomer, indicating van der Waals (vdW) interaction between them; however, the fluorescence lifetime was drastically shortened. In contrast, the TCNQ-Bz complex gave a broad electronic spectrum. The study of the fluorescence and its time profile in TCNQ/Bz/hexane solution clearly shows the formation of the CT complex between TCNQ and Bz. Based on the experimental results and density functional theory (DFT) calculations, we propose that in the TCNQ monomer and TCNQ-ACN complex the S-1 (pi pi*) state is coupled to the intramolecular CT state, while the S-1 state of TCNQ in the TCNQ-Bz complex is more strongly coupled to the intermolecular CT state

ベンゼン クラスター ノ レーザー ブンコウガクテキ ケンキュウ

京都大学0048新制・課程博士博士(理学)甲第9164号理博第2396号新制||理||1244(附属図書館)UT51-2001-N210京都大学大学院理学研究科化学専攻(主査)教授 鷲田 伸明, 教授 梶本 興亜, 助教授 大島 康裕学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDA

Time-Resolved Photoresponse Measurements of the Electrical Conductivity of the Quasi-Two-Dimensional Organic Superconductor β-(BEDT-TTF)2I3 Using a Nanosecond Laser Pulse

Time-resolved photoresponses in resistance have been measured following the nanosecond laser pulse excitation for the quasi-two-dimensional organic superconductors of hydrogenated and deuterated β-(BEDT-TTF)2I3 [BEDT-TTF = bis-(ethylenedithio)tetrathiafulvalene], which show two different superconducting states with high-Tc and low-Tc at temperatures near the critical temperatures. A transient increase of the resistance is induced by photoirradiation at all the temperatures, but a marked temperature dependence of the decay time is observed at temperatures close to the high-Tc phase transition temperature; the decay rate becomes faster and then becomes constant in both compounds, as the temperature decreases across the high-Tc phase transition temperature. The temperature dependence of the photoresponse intensity is different from the one expected from the bolometric effects, indicating the presence of the nonbolometric photoresponse. A possible mechanism explaining the photoresponse of the conductivity is discussed, based on the isotope effect on the photoresponse. A comparison is also made between β-(BEDT-TTF)2I3 and κ-(BEDT-TTF)2Cu[N(CN)2]Br for the transient photoresponse in resistance at temperatures across the metal-superconductor phase transition temperature

Molecular-based light-activated thyristor

A photoinduced electrical conductivity switching is observed in the molecular conductor of -[bis(ethylenedithio)tetrathiafulvalene]2I3 at different temperatures with different irradiation light intensities. The threshold voltage for the differential-negative-resistance effect appearing in the current-voltage characteristic curve decreases and increases, respectively, as the light intensity is increased and as the temperature decreases below the insulator-metal phase transition. The potential application of molecular conductor in bidirectional light-activated thyristor devices is demonstrated