We propose a one-dimensional (1D) diffusion equation (heat equation) for systems in which the diffusion constant (thermal diffusivity) varies alternately with a spatial period $a$. We solve the time evolution of the field (temperature) profile from a
given initial distribution, by diagonalising the Hamiltonian, i.e., the Laplacian with alternating diffusion constants, and expanding the temperature profile by its eigenstates. We show that there are basically phases with or without edge states. The edge states affect the heat conduction around heat baths. In particular, rapid heat transfer to heat baths would be observed in a short time regime, which is estimated to be $t<10^{-2}$s for $asim 10^{-3}$m system and $t< 1$s for $asim 10^{-2}$m system composed of two kinds of familiar metals such as titanium, zirconium and aluminium, gold, etc. We also discuss the effective lattice model which simplifies the calculation of edge states up to high energy. It is suggested that these high energy edge states also contribute to very rapid heat conduction in a very short time regime.
Hybridization of Bogoliubov quasiparticles (BQPs) between the CuO$_2$ layers in the triple-layer cuprate high-temperature superconductor Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+delta}$ is studied by angle-resolved photoemission spectroscopy (ARPES). In the su
perconducting state, an anti-crossing gap opens between the outer- and inner-BQP bands, which we attribute primarily to interlayer single-particle hopping with possible contributions from interlayer Cooper pairing. We find that the $d$-wave superconducting gap of both BQP bands smoothly develops with momentum without abrupt jump in contrast to a previous ARPES study. Hybridization between the BQPs also gradually increases in going from the off-nodal to the anti-nodal region, which is explained by the momentum-dependence of the interlayer single-particle hopping. As possible mechanisms for the enhancement of the superconducting transition temperature, the hybridization between the BQPs, as well as the combination of phonon modes of the triple CuO$_2$ layers and spin fluctuations are discussed.
We report on robust measurements of elemental abundances of the Type IIn supernova SN 1978K, based on the high-resolution X-ray spectrum obtained with the Reflection Grating Spectrometer (RGS) onboard XMM-Newton. The RGS clearly resolves a number of
emission lines, including N Ly$alpha$, O Ly$alpha$, O Ly$beta$, Fe XVII, Fe XVIII, Ne He$alpha$ and Ne Ly$alpha$ for the first time from SN 1978K. The X-ray spectrum can be represented by an absorbed, two-temperature thermal emission model, with temperatures of $kT sim 0.6$ keV and $2.7$ keV. The elemental abundances are obtained to be N $=$ $2.36_{-0.80}^{+0.88}$, O $=$ $0.20 pm{0.05}$, Ne $=$ $0.47 pm{0.12}$, Fe $=$ $0.15_{-0.02}^{+0.01}$ times the solar values. The low metal abundances except for N show that the X-ray emitting plasma originates from the circumstellar medium blown by the progenitor star. The abundances of N and O are far from CNO-equilibrium abundances expected for the surface composition of a luminous blue variable, and resemble the H-rich envelope of less-massive stars with masses of 10-25 M$_odot$. Together with other peculiar properties of SN 1978K, i.e., a low expansion velocity of 500-1000 km s$^{-1}$ and SN IIn-like optical spectra, we propose that SN 1978K is a result of either an electron-capture SN from a super asymptotic giant branch star, or a weak Fe core-collapse explosion of a relatively low-mass ($sim$10 M$_odot$) or high-mass ($sim$20-25 M$_odot$) red supergiant star. However, these scenarios can not naturally explain the high mass-loss rate of the order of $dot{M} sim 10^{-3} rm{M_{odot} yr^{-1}}$ over $gtrsim$1000 yr before the explosion, which is inferred by this work as well as many other earlier studies. Further theoretical studies are required to explain the high mass-loss rates at the final evolutionary stages of massive stars.
We have investigated the superconducting gap of optimally doped Ba(Fe$_{0.65}$Ru$_{0.35}$)$_2$As$_2$ by angle-resolved photoemission spectroscopy (APRES) using bulk-sensitive 7 eV laser and synchrotron radiation. It was found that the gap is isotropi
c in the $k_x$-$k_y$ plane both on the electron and hole Fermi surfaces (FSs). The gap magnitudes of two resolved hole FSs show similar $k_z$ dependences and decrease as $k_z$ approaches $sim$ 2$pi$/$c$ (i.e., around the Z point) unlike the other Fe-based superconductors reported so far, where the superconducting gap of only one hole FS shows a strong $k_z$ dependence. This unique gap structure can be understood in the scenario that the $d_{z^2}$ orbital character is mixed into both hole FSs due to the finite spin-orbit coupling between almost degenerate FSs and is reproduced by calculations within the random phase approximation including the spin-orbit coupling.
We have performed an angle-resolved photoemission study of the nodal quasi-particle spectra of the high-Tc cuprate tri-layer Bi2Sr2Ca2Cu3O10+d (Tc~ 110 K). The spectral weight Z of the nodal quasi-particle increases with decreasing temperature across
the Tc. Such a temperature dependence is qualitatively similar to that of the coherence peak intensity in the anti nodal region of various high-Tc cuprates although the nodal spectral weight remains finite and large above Tc. We attribute this observation to the reduction of electron correlation strength in going from the normal metallic state to the superconducting state, a characteristic behavior of a superconductor with strong electron correlation.
We have performed an angle-resolved photoemission spectroscopy (ARPES) study of BaNi$_2$P$_2$ which shows a superconducting transition at $T_c$ $sim$ 2.5 K. We observed hole and electron Fermi surfaces (FSs) around the Brillouin zone center and corne
r, respectively, and the shapes of the hole FSs dramatically changed with photon energy, indicating strong three-dimensionality. The observed FSs are consistent with band-structure calculation and de Haas-van Alphen measurements. The mass enhancement factors estimated in the normal state were $m^*$/$m_b$ $leq$ 2, indicating weak electron correlation compared to typical iron-pnictide superconductors. An electron-like Fermi surface around the Z point was observed in contrast with BaNi$_2$As$_2$ and may be related to the higher $T_c$ of BaNi$_2$P$_2$.
We have studied the electronic structure of Ba(Fe$_{1-x}$Mn$_{x}$)$_{2}$As$_{2}$ ($x$=0.08), which fails to become a superconductor in spite of the formal hole doping like Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$, by photoemission spectroscopy and X-ray abs
orption spectroscopy (XAS). With decreasing temperature, a transition from the paramagnetic phase to the antiferromagnetic phase was clearly observed by angle-resolved photoemission spectroscopy. XAS results indicated that the substituted Mn atoms form a strongly hybridized ground state. Resonance-photoemission spectra at the Mn $L_{3}$ edge revealed that the Mn 3d partial density of states is distributed over a wide energy range of 2-13 eV below the Fermi level ($E_F$), with little contribution around $E_F$. This indicates that the dopant Mn 3$d$ states are localized in spite of the strong Mn 3d-As $4p$ hybridization and split into the occupied and unoccupied parts due to the on-site Coulomb and exchange interaction. The absence of superconductivity in Ba(Fe$_{1-x}$Mn$_{x}$)$_{2}$As$_{2}$ can thus be ascribed both to the absence of carrier doping in the FeAs plane, and to the strong stabilizaiton of the antiferromagnetic order by the Mn impurities.
In the iron pnictide superconductors, two distinct unconventional mechanisms of superconductivity have been put forth: One is mediated by spin fluctuations leading to the s+- state with sign change of superconducting gap between the hole and electron
bands, and the other is orbital fluctuations which favor the s++ state without sign reversal. Here we report direct observation of peculiar momentum-dependent anisotropy in the superconducting gap from angle-resolved photoemission spectroscopy (ARPES) in BaFe2(As1-xPx)2 (Tc=30 K). The large anisotropy found only in the electron Fermi surface (FS) and the nearly isotropic gap on the entire hole FSs are together consistent with modified s+- gap with nodal loops, which can be theoretically reproduced by considering both spin and orbital fluctuations whose competition generates the gap modulation. This indicates that these two fluctuations are nearly equally important to the high-Tc superconductivity in this system.
Relationship between the superconducting gap and the pseudogap has been the subject of controversies. In order to clarify this issue, we have studied the superconducting gap and pseudogap of the high-Tc superconductor La2-xSrxCuO4 (x=0.10, 0.14) by a
ngle-resolved photoemission spectroscopy (ARPES). Through the analysis of the ARPES spectra above and below Tc, we have identified a superconducting coherence peak even in the anti-nodal region on top of the pseudogap of a larger energy scale. The superconducting peak energy nearly follows the pure d-wave form. The d-wave order parameter Delta_0 [defined by Delta(k)=Delta_0(cos(kxa)-cos(kya)) ] for x=0.10 and 0.14 are nearly the same, Delta_0 ~ 12-14 meV, leading to strong coupling 2Delta_0/kB Tc ~ 10. The present result indicates that the pseudogap and the superconducting gap are distinct phenomena and can be described by the two-gap scenario.
We have performed an angle-resolved photoemission study of the hole-overdoped iron pnictide superconductor KFe2As2, which shows a low Tc of ~4 K. Most of the observed Fermi surfaces show nearly two-dimensional shapes, while a band near the Fermi leve
l shows a strong dispersion along the kz direction and forms a small three-dimensional hole pocket centered at the Z point, as predicted by band-structure calculation. However, hole Fermi surfaces of yz and zx orbital character centered at the Gamma point of the two-dimensional Brillouin zone are smaller than those predicted by the calculation while the other hole Fermi surfaces of xy orbital character is much larger. Clover-shaped hole Fermi surfaces around the corner of the 2D BZ are also larger than those predicted by the calculation. These observations are consistent with the de Haas-van Alphen measurement and indicate orbital-dependent electron correlation effects. The effective masses of the energy bands show moderate to strong enhancement, partly due to electron correlation and partly due to energy shifts from the calculated band structure.
