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New measurements of photofission and photoneutron reactions on $^{238}$U and $^{232}$Th in the Giant Dipole Resonance (GDR) energy region have been performed at the laser Compton-scattering $\gamma$-ray source of the NewSUBARU synchrotron radiation facility using a high-and-flat efficiency moderated $^3$He detection array. The neutron-multiplicity sorting of high-multiplicity fission neutron coincidence events has been performed using a dedicated energy dependent, multiple firing statistical treatment. The photoneutron $(\gamma,\,in)$ with $i$~=~1~--~3 and photofission $(\gamma,\,F)$ reactions have been discriminated by considering a Gaussian distribution of prompt-fission-neutron (PFN) multiplicities predicted by the theory of evaporation in sequential neutron emission from excited fission fragments. We report experimental $(\gamma,\,n)$, $(\gamma,\,2n)$, $(\gamma,\,3n)$ and $(\gamma,\,F)$ cross sections, average energies of PFNs and of $(\gamma,\,in)$ photoneutrons, as well as the mean number of PFNs per fission act and the width of the PFNs multiplicity distribution. Based on these primary experimental results and combined with reasonable assumptions, we extract also the first- and second-chance fission contributions. The new experimental results are compared with statistical-model calculations performed with the EMPIRE-3.2 Malta and TALYS-1.964 codes on the present data and with prompt fission emission calculations obtained with the Los Alamos model in the frame of the most probable fragmentation approach with and without sequential emission.

Nd2Ir2O7 is a correlated semimetal with the pyrochlore structure, in which competing spin-orbit coupling and electron-electron interactions are believed to induce a time-reversal symmetry broken Weyl semimetal phase characterized by pairs of topologically protected Dirac points at the Fermi energy. However, the emergent properties in these materials are far from clear, and exotic new states of matter have been conjectured. Here we demonstrate optically that at low temperatures the free carrier spectral weight is proportional to T^2 where T is the temperature, as expected for massless Dirac electrons. However, we do {\em not} observe the corresponding T^3 term in the specific heat. That the system is not in a Fermi liquid state is further corroborated by the "Planckian" T-linear temperature dependence of the momentum relaxation rate and the progressive opening of a correlation-induced gap at low temperatures. These observations can not be reconciled within the framework of band theory of electron-like quasiparticles and point toward the effective decoupling of the charge transport from the single particle sector., Comment: 7 pages, 5 figures

Dirac and Weyl semimetals with linearly crossing bands are the focus of much recent interest in condensed matter physics. Although they host fascinating phenomena, their physics can be understood in terms of weakly interacting electrons. In contrast, more than 40 years ago, Abrikosov pointed out that quadratic band touchings are generically strongly interacting. We have performed terahertz spectroscopy on films of the conducting pyrochlore Pr$_2$Ir$_2$O$_7$, which has been shown to host a quadratic band touching. A dielectric constant as large as $\tilde{\varepsilon }/\epsilon_0 \sim 180 $ is observed at low temperatures. In such systems the dielectric constant is a measure of the relative scale of interactions, which are therefore in our material almost two orders of magnitude larger than the kinetic energy. Despite this, the scattering rate exhibits a $T^2$ dependence, which shows that for finite doping a Fermi liquid state survives, however with a scattering rate close to the maximal value allowed., Comment: To appear in Nature Communications (2017)

We have estimated the critical exponent describing the divergence of the localization length at the metal-quantum spin Hall insulator transition. The critical exponent for the metal-ordinary insulator transition in quantum spin Hall systems is known to be consistent with that of topologically trivial symplectic systems. However, the precise estimation of the critical exponent for the metal-quantum spin Hall insulator transition proved to be problematic because of the existence, in this case, of edge states in the localized phase. We have overcome this difficulty by analyzing the second smallest positive Lyapunov exponent instead of the smallest positive Lyapunov exponent. We find a value for the critical exponent $\nu=2.73 \pm 0.02$ that is consistent with that for topologically trivial symplectic systems., Comment: 5 pages, 4 figures, submitted to the proceedings of Localisation 2011

Time-resolved photoelectron spectroscopy (trPES) can directly detect transient electronic structure, thus bringing out its promising potential to clarify nonequilibrium processes arising in condensed matters. Here we report the result of core-level (CL) trPES on 1T-TaS2, realized by developing a high-intensity 60 eV laser obtained by high-order harmonic (HH) generation. Ta4f CL-trPES offers the transient amplitude of the charge-density-wave (CDW), via the site-selective and real-time observation of Ta electrons. The present result indicates an ultrafast photoinduced melting and recovery of CDW amplitude, followed by a peculiar long-life oscillation (i.e. collective amplitudon excitation) accompanying the transfer of 0.01 electrons among adjacent Ta atoms. CL-trPES offers a broad range of opportunities for investigating the ultrafast atom-specific electron dynamics in photo-related phenomena of interest.

We report on the electronic structure of the perovskite oxide CaCrO3 using valence-band, core-level, and Cr 2p - 3d resonant photoemission spectroscopy (PES). Despite its antiferromagnetic order, a clear Fermi edge characteristic of a metal with dominant Cr 3d character is observed in the valence band spectrum. The Cr 3d single particle density of states are spread over 2 eV, with the photoemission spectral weight distributed in two peaks centered at ~ 1.2 eV and 0.2 eV below EF, suggestive of the coherent and incoherent states resulting from strong electron-electron correlations. Resonant PES across the Cr 2p - 3d threshold identifies a 'two-hole' correlation satellite and yields an on-site Coulomb energy U ~4.8 eV. The metallic DOS at EF is also reflected through the presence of a well-screened feature at low binding energy side of the Cr 2p core-level spectrum. X-ray absorption spectroscopy (XAS) at Cr L3,2 and O K edges exhibit small temperature dependent changes that point towards a small change in Cr-O hybridization. The multiplet splitting in Cr 2p core level spectrum as well as the spectral shape of the Cr XAS can be reproduced using cluster model calculations which favour a negative value for charge transfer energy between the Cr 3d and O 2p states. The overall results indicate that CaCrO3 is a strongly hybridized antiferromagnetic metal, lying in the regime intermediate to Mott-Hubbard and charge-transfer systems.

We study the surface and bulk electronic structure of the room-temperature ferromagnet Co:TiO2 anatase films using soft and hard x-ray photoemission spectroscopy with probe sensitivities of ~1 nm and ~10 nm, respectively. We obtain direct evidence of metallic Ti$^{3+}$ states in the bulk, which get suppressed to give a surface semiconductor, thus indicating a surface-bulk dichotomy. X-ray absorption and high-sensitivity resonant photoemission spectroscopy reveal Ti$^{3+}$ electrons at the Fermi level (E$_F$) and high-spin Co$^{2+}$ electrons occurring away from E$_F$. The results show the importance of the charge neutrality condition: Co$^{2+}$ + V$_{O}$$^{2-}$ + 2Ti$^{4+}$ $\leftrightarrow$ Co$^{2+}$ + 2Ti$^{3+}$ (V$_O$ is oxygen vacancy), which gives rise to the elusive Ti 3d carriers mediating ferromagnetism via the Co 3d-O 2p-Ti 3d exchange interaction pathway of the occupied orbitals., Comment: 4 pages, 4 figures

We study numerically the charge conductance distributions of disordered quantum spin-Hall (QSH) systems using a quantum network model. We have found that the conductance distribution at the metal-QSH insulator transition is clearly different from that at the metal-ordinary insulator transition. Thus the critical conductance distribution is sensitive not only to the boundary condition but also to the presence of edge states in the adjacent insulating phase. We have also calculated the point-contact conductance. Even when the two-terminal conductance is approximately quantized, we find large fluctuations in the point-contact conductance. Furthermore, we have found a semi-circular relation between the average of the point-contact conductance and its fluctuation., Comment: 9 pages, 17 figures, published version

We investigate numerically the spin polarization of the current in the presence of Rashba spin-orbit interaction in a T-shaped conductor proposed by A.A. Kiselev and K.W. Kim (Appl. Phys. Lett. {\bf 78} 775 (2001)). The recursive Green function method is used to calculate the three terminal spin dependent transmission probabilities. We focus on single-channel transport and show that the spin polarization becomes nearly 100 % with a conductance close to $e^{2}/h$ for sufficiently strong spin-orbit coupling. This is interpreted by the fact that electrons with opposite spin states are deflected into an opposite terminal by the spin dependent Lorentz force. The influence of the disorder on the predicted effect is also discussed. Cases for multi-channel transport are studied in connection with experiments.

An overview of the random network model invented by Chalker and Coddington, and its generalizations, is provided. After a short introduction into the physics of the Integer Quantum Hall Effect, which historically has been the motivation for introducing the network model, the percolation model for electrons in spatial dimension 2 in a strong perpendicular magnetic field and a spatially correlated random potential is described. Based on this, the network model is established, using the concepts of percolating probability amplitude and tunneling. Its localization properties and its behavior at the critical point are discussed including a short survey on the statistics of energy levels and wave function amplitudes. Magneto-transport is reviewed with emphasis on some new results on conductance distributions. Generalizations are performed by establishing equivalent Hamiltonians. In particular, the significance of mappings to the Dirac model and the two dimensional Ising model are discussed. A description of renormalization group treatments is given. The classification of two dimensional random systems according to their symmetries is outlined. This provides access to the complete set of quantum phase transitions like the thermal Hall transition and the spin quantum Hall transition in two dimension. The supersymmetric effective field theory for the critical properties of network models is formulated. The network model is extended to higher dimensions including remarks on the chiral metal phase at the surface of a multi-layer quantum Hall system., Comment: 176 pages, final version, references corrected

This is a list of open problems on invariants of knots and 3-manifolds with expositions of their history, background, significance, or importance. This list was made by editing open problems given in problem sessions in the workshop and seminars on `Invariants of Knots and 3-Manifolds' held at Kyoto in 2001., Comment: Edited by T. Ohtsuki. Published by Geometry and Topology Monographs at http://www.maths.warwick.ac.uk/gt/GTMon4/paper24.abs.html

We perform exact coupled-channels calculations, taking into account properly the effects of Coulomb coupling and the finite excitation energy of collective excitations in the colliding nuclei, for three Fm formation reactions, $^{37}$Cl + $^{209}$Bi, $^{45}$Sc + $^{197}$Au, and $^{59}$Co + $^{181}$Ta. For the $^{37}$Cl + $^{209}$Bi and $^{45}$Sc + $^{197}$Au reactions, those calculations well reproduce the experimental total fission cross sections, and a part of the extra-push phenomena can be explained in terms of the Coulomb excitations to multi-phonon states. On the other hand, for the heaviest system, the deep-inelastic collisions become much more significant, and the fission cross sections are strongly overestimated. We also discuss the surprisingly large surface diffuseness parameters required to fit recent high-precision fusion data for medium-heavy systems, in connection with the fusion supression observed in massive systems., Comment: 10 pages, 6 ps figures. Uses aipxfm.sty. A talk given at the Tours Symposium on Nuclear Physics V, August 26 - 29, 2003, Tours, France

Electron transport through disordered systems that include spin scatterers is studied numerically. We consider three kinds of magnetic impurities: the Ising, the XY and the Heisenberg. By extending the transfer matrix method to include the spin degree of freedom, the two terminal conductance is calculated. The variance of conductance is halved as the number of spin components of the magnetic impurities increases. Application of the Zeeman field in the lead causes a further halving of the variance under certain conditions., Comment: to be published in Phys. Rev. B

Sharp localization transitions of chiral edge states in disordered quantum wires, subject to strong magnetic field, are shown to be driven by crossovers from two- to one-dimensional localization of bulk states. As a result, the two-terminal conductance is found to exhibit at zero temperature discontinuous transitions between {\it exactly} integer plateau values and zero, reminiscent of first order phase transitions. We discuss the corresponding phase diagram. The spin of the electrons is shown to result in a multitude of phases, when the spin degeneracy is lifted by the Zeeman energy. The width of conductance plateaus is found to depend sensitively on the spin flip rate $1/\tau_s$., Comment: 4 pages, 3 figures

The two terminal conductance for two dimensional systems is calculated in the presence of the spin-orbit scattering. The level statistics of the transmission eigenvalue is shown to be sensitive to the asymmetry of the spin population in the lead. The nearest neighbor spacing is GUE instead of GSE when sufficiently large Zeeman splitting is assumed in one of the lead., Comment: accepted in Proceedings of Localisation 2002 Conference, Tokyo, Japan (to be published as supplement of J. Phys. Soc. Japan)

We present a theoretical study of spin-dependent transport through a ferromagnetic domain wall. With an increase of the number of components of the exchange coupling, we have observed that the variance of the conductance becomes half. As the strength of the domain wall magnetization is increased, negative magnetoresistance is also observed., Comment: accepted in Proceedings of Localisation 2002 Conference, Tokyo, Japan (to be published as supplement of J. Phys. Soc. Japan)

The Anderson transitions in a random magnetic field in three dimensions are investigated numerically. The critical behavior near the transition point is analyzed in detail by means of the transfer matrix method with high accuracy for systems both with and without an additional random scalar potential. We find the critical exponent $\nu$ for the localization length to be $1.45 \pm 0.09$ with a strong random scalar potential. Without it, the exponent is smaller but increases with the system sizes and extrapolates to the above value within the error bars. These results support the conventional classification of universality classes due to symmetry. Fractal dimensionality of the wave function at the critical point is also estimated by the equation-of-motion method., Comment: 9 pages, 3 figures, to appear in Annalen der Physik

The Anderson transition in three dimensions in a randomly varying magnetic flux is investigated in detail by means of the transfer matrix method with high accuracy. Both, systems with and without an additional random scalar potential are considered. We find a critical exponent of $\nu=1.45\pm0.09$ with random scalar potential. Without it, $\nu$ is smaller but increases with the system size and extrapolates within the error bars to a value close to the above. The present results support the conventional classification of universality classes due to symmetry., Comment: 4 pages, 2 figures, to appear in Phys. Rev. B

The Anderson transition in a 3D system with symplectic symmetry is investigated numerically. From a one-parameter scaling analysis the critical exponent $\nu$ of the localization length is extracted and estimated to be $\nu = 1.3 \pm 0.2$. The level statistics at the critical point are also analyzed and shown to be scale independent. The form of the energy level spacing distribution $P(s)$ at the critical point is found to be different from that for the orthogonal ensemble suggesting that the breaking of spin rotation symmetry is relevant at the critical point., Comment: 4 pages, revtex, to appear in Physical Review Letters. 3 figures available on request either by fax or normal mail from tkawa@eagle.issp.u-tokyo.ac.jp or ohtsuki@hoffman.cc.sophia.ac.jp

The scaling property of level statistics in the quantum Hall regime, i.e. 2D disordered electron systems subject to strong magnetic fields, is analyzed numerically in the light of the random matrix theory. The energy dependences of the effective level repulsion parameter, the two level correlation, the GUE-GOE crossover parameter, and the rigidity (or $\Delta_3$-statistics) of the level distributions are investigated for different system sizes by unfolding the original data and by dividing the unfolded spectrum into small regions. It is shown that the critical exponent of the localization length as a function of energy can be determined through the energy dependence of the level statistics. The analyses are carried out not only for the lowest Landau band (LB) but also for the second lowest LB. Furthermore the effect of finite range of disordered potential is studied. The short-ranged potential case in the second lowest LB is found to be pathological as in other studies of critical behavior, and it is confirmed that this pathological behavior is improved in the case of disordered potential with finite ranges., Comment: 16 pages, latex, 10 figures (postscript figures available on request to ono@polaron.ph.sci.toho-u.ac.jp), to be published in J. Phys. Soc. Jpn. vol. 65 (1996) No. 6B; misprint in eq.(5.3) is corrected