Nuclear fission: The "onset of dissipation" from a microscopic point of view

Semi-analytical expressions are suggested for the temperature dependence of those combinations of transport coefficients which govern the fission process. This is based on experience with numerical calculations within the linear response approach and the locally harmonic approximation. A reduced version of the latter is seen to comply with Kramers' simplified picture of fission. It is argued that for variable inertia his formula has to be generalized, as already required by the need that for overdamped motion the inertia must not appear at all. This situation may already occur above T=2 MeV, where the rate is determined by the Smoluchowski equation. Consequently, comparison with experimental results do not give information on the effective damping rate, as often claimed, but on a special combination of local stiffnesses and the friction coefficient calculated at the barrier.Comment: 31 pages, LaTex, 9 postscript figures; final, more concise version, accepted for publication in PRC, with new arguments about the T-dependence of the inertia; e-mail: [email protected]

Possible high TcT_c superconductivity mediated by antiferromagnetic spin fluctuations in systems with Fermi surface pockets

We propose that if there are two small pocket-like Fermi surfaces, and the spin susceptibility is pronounced around a wave vector {\bf Q} that bridges the two pockets, the spin-singlet superconductivity mediated by spin fluctuations may have a high transition temperature. Using the fluctuation exchange approximation, this idea is confirmed for the Hubbard on a lattice with alternating hopping integrals, for which $T_c$ is estimated to be almost an order of magnitude larger than those for systems with a large connected Fermi surface.Comment: 5 pages, uses RevTe

Low-temperature specific heat for ferromagnetic and antiferromagnetic orders in CaRu1-xMnxO3

Low-temperature specific heat of CaRu1-xMnxO3 was measured to clarify the role of d electrons in ferromagnetic and antiferromagnetic orders observed above x=0.2. Specific heat divided by temperature C_p/T is found to roughly follow a T^2 function, and relatively large magnitudes of electronic specific heat coefficient gamma were obtained in wide x range. In particular, gamma is unchanged from the value at x=0 (84 mJ/K^2 mol) in the paramagnetic state for x<=0.1, but linearly reduced with increasing x above x= 0.2. These features of gamma strongly suggest that itinerant d electrons are tightly coupled with the evolution of magnetic orders in small and intermediate Mn concentrations.Comment: 4 pages, 2 figures, to be published in J. Phys.: Conf. Ser. (SCES 2011, Cambridge, UK

High Accuracy and Automatic Measurement of the Pattern Linewidth on Very Large Scale Integrated Circuits

High accuracy measurement of pattern linewidth is particularly important in Very Large Scale Integrated Circuits (VLSI) manufacturing. The measurement of pattern linewidth has been done by optical methods. However, the optical methods have several problems: as the measured value depends on slope angle at pattern edge, thickness and optical property of film and also substrate, there exists a large difference in size (0.3 μm) between the defined edge and the true edge in case of photoresist linewidth measurements. Especially, the optical methods have severe problems to measure bottom of pattern edge and are unsuitable to measure pattern linewidth in VLSI\u27s manufacturing. The secondary electron signal obtained by electron beam irradiation can be used to measure pattern linewidth with high accuracy. In order to avoid radiation damage and contamination during in-process measurement, low primary electron energy (1 keV) and low dosage of primary electrons (1X1020electrons/cm2) are used. As secondary electron signal includes much random noise, signal averaging and smoothing methods for random noise reduction are utilized. The automatic detection of bottom edge from secondary electron profile is achieved by detecting the increasing point of line profile which corresponds to the cross point of the average line and the slope line. The linewidths obtained by this method agree with the linewidths calculated from the pattern pitch of cross section image obtained by scanning electron microscopy(SEM) within the error of 0.04μm

Ground state of the three-band Hubbard model

The ground state of the two-dimensional three-band Hubbard model in oxide superconductors is investigated by using the variational Monte Carlo method. The Gutzwiller-projected BCS and spin- density wave (SDW) functions are employed in the search for a possible ground state with respect to dependences on electron density. Antiferromagnetic correlations are considerably enhanced near half-filling. It is shown that the d-wave state may exist away from half-filling for both the hole and electron doping cases. The overall structure of the phase diagram obtained by the calculations qualitatively agrees with experimental indications. The superconducting condensation energy is in reasonable agreement with the experimental value obtained from specific heat and critical magnetic field measurements for optimally doped samples. The inhomogeneous SDW state is also examined near 1/8-hole doping.Comment: 10 pages, 17 figure

Localizations in coupled electronic chains

We studied effects of random potentials and roles of electron-electron interactions in the gapless phase of coupled Hubbard chains, using a renormalization group technique. For non-interacting electrons, we obtained the localization length proportional to the number of chains, as already shown in the other approaches. For interacting electrons, the localization length is longer for stronger interactions, that is, the interactions counteract the random potentials. Accordingly, the localization length is not a simple linear function of the number of chains. This interaction effect is strongest when there is only a single chain. We also calculate the effects of interactions and random potentials on charge stiffness.Comment: no figure, to appear in Phys. Rev.

Unconventional charge density wave in the organic conductor alpha-(BEDT-TTF)_2KHg(SCN)_4

The low temperature phase (LTP) of alpha-(BEDT-TTF)_2KHg(SCN)_4 salt is known for its surprising angular dependent magnetoresistance (ADMR), which has been studied intensively in the last decade. However, the nature of the LTP has not been understood until now. Here we analyse theoretically ADMR in unconventional (or nodal) charge density wave (UCDW). In magnetic field the quasiparticle spectrum in UCDW is quantized, which gives rise to spectacular ADMR. The present model accounts for many striking features of ADMR data in alpha-(BEDT-TTF)_2KHg(SCN)_4.Comment: 5 pages, 6 figure

Persistent current of two-chain Hubbard model with impurities

The interplay between impurities and interactions is studied in the gapless phase of two-chain Hubbard model in order to see how the screening of impurity potentials due to repulsive interactions in single-chain model will be changed by increasing the number of channels. Renormalization group calculations show that charge stiffness, and hence persistent current, of the two-chain model are less enhanced by interactions than single chain case.Comment: 4 Pages, RevTeX, No figures, Submitted to PR

Spin-Density-Wave Phase Transitions in Quasi-One-Dimensional Dimerized Quarter-Filled Organic Conductors

We have studied spin density wave (SDW) phase transitions in dimerized quarter-filled Hubbard chains weakly coupled via interchain one-particle hopping, $t_{b0}$. It is shown that there exists a critical value of $t_{b0}$, $t_{b}^\ast$, between the incoherent metal regime ($t_{b0}<t_{b}^\ast$) and the Fermi liquid regime ($t_{b0}>t_{b}^\ast$) in the metallic phase above the SDW transition temperature. By using the 2-loop perturbative renormalization-group approach together with the random-phase-approximation, we propose a SDW phase diagram covering both of the regimes. The SDW phase transition from the incoherent metal phase for $t_{b0}<t_{b}^\ast$ is caused by growth of the intrachain electron-electron umklapp scattering toward low temperatures, which is regarded as preformation of the Mott gap. We discuss relevance of the present result to the SDW phase transitions in the quasi-one-dimensional dimerized quarter-filled organic conductors, (TMTTF)$_2$X and (TMTSF)$_2$X.Comment: 19 pages, 13 eps figures, uses jpsj.sty, corrected typo in the text and figures, no changes to the paper, to appear in J. Phys. Soc. Jpn. 68, No.8 (1999