We present a quantized non-Abelian Berry phase for time-reversal-invariant systems such as the quantum spin Hall effect. An ordinary Berry phase is defined by an integral of Berry’s gauge potential along a loop (an integral of the Chern–Simons one-form), whereas we propose that an integral over a five-dimensional parameter space (an integral of the Chern–Simons five-form) is suitable for defining a non-Abelian Berry phase. We study its global topological aspects and show that it is indeed quantized into two values. We also discuss its close relationship with nonperturbative anomalies.

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We succeeded in experimentally demonstrating that a series of two-dimensional maps of a dynamical structure factor in momentum–energy space with multiple incident energies can be simultaneously obtained by one measurement. This method reduces the dead time of time-of-flight measurement, and thus, it markedly increases the measurement efficiency. Our achievement realized using the Fermi chopper spectrometer 4SEASONS in J-PARC is expected to open up new possibilities of inelastic neutron scattering measurements.

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A target for a laser plasma ion source is improved by adding micro tips to a polytetrafluoroethylene thin foil that originally has a fibrous microstructure. C⁶⁺ ions, deuterons, and protons are generated by irradiation of the target with laser pulses whose maximum intensity was 4.8×10¹⁸ W/cm². The additional micro-tip structure clearly increases the yields of deuterons and C⁶⁺ ions, although that of the protons was not altered. The maximum energies of all the ion species are almost the same between the new and the conventional targets. They were ∼0.9, ∼1, and ∼6 MeV for the protons, deuterons, and C⁶⁺ ions, respectively.

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Topological effects on spin frustration in equilateral triangle S=3⁄2 spin tubes formed in CsCrF₄ were studied by magnetic susceptibility, heat capacity [C(T)], and electron spin resonance experiments. The experimental data show that there is no magnetic long-range order down to T=1.3 K, and that no spin gap due to a chiral spin structure appears. Furthermore, since the C(T) curve has a T-linear component, a gapless spin-liquid ground state in one-dimensional antiferromagnets, the so-called Tomonaga–Luttinger liquid, is realized. This is characteristic of equilateral triangle spin tubes with S = half-integer.

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The magnetization of LaCoO₃ shows a magnetic transition induced by level crossing at a magnetic field of 60 T below 25 K, which is consistent with the energy diagram determined from electron spin resonance experiments. However, the amount of Co ions with g=3.35 contributing to the magnetic transition is sample-dependent and at most 14% of the total Co ions in LaCoO₃. We found that the rest of the Co ions also contribute to the magnetization, which is a maximum at around 100 K. We analyzed the magnetization assuming two kinds of Co species, Co_I and Co_II, both of which have the nonmagnetic ground state. The energies and the g values of the magnetic excited states are 135 K and 3.35 for Co_I, and 250–260 K and 1.9–2.0 for Co_II, respectively. Co_I ions are suggested to be associated with oxygen vacancies and the surface of LaCoO₃.

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The pressure dependence of superconducting transition temperature T_c has been investigated through the DC magnetic measurements for FeSe_0.8 and FeSe_1.0. For both samples, with increasing pressure P, the T_c–P curve exhibits a two-step increase, showing a local maximum of ∼11 K at P∼1.0 GPa and a rapid increase with an extremely large pressure coefficient for P>1.5 GPa. T_c saturates at ∼25 K (21 K) in FeSe_1.0 (FeSe_0.8) for P>3 GPa. A rapid decrease in superconducting volume fraction is observed with an increase in T_c above 1.5 GPa, suggesting the presence of electronic inhomogeneity.

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The complex phase transition of the magnetic long-range order in Fe_0.7Co_0.3Si has been investigated by small-angle neutron scattering (SANS) measurement at low temperatures under an external magnetic field. A variety of scattering patterns, such as ring, crescent-shaped, and diffusive spots, were observed by changing temperature and applying a magnetic field. The results could be interpreted by an analogy of the phase transition of the liquid crystal when the net magnetization is regarded as the director of the liquid crystal.

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Single-particle excitation spectra of γ-Fe in the paramagnetic state have been investigated by means of the first-principles dynamical coherent potential approximation theory which has recently been developed. It is found that the central peak in the density of states consisting of the t_2g bands is destroyed by electron correlations, and the Mott–Hubbard type correlated bands appear. The results indicate that the γ-Fe can behave as correlated electrons at high temperatures.

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Thin-film transistors (TFTs) with amorphous InGaZnO₄ as a channel layer are known to exhibit high field-effect mobility. We studied the characteristic of the accumulated carriers in this TFT by optical spectroscopy and observed Drude absorption and oscillation in the transmittance spectrum of the channel region appearing with an applied gate voltage. The scattering rate of the carriers in the accumulation layers estimated from the optical spectrum is h⁄τ_AL=0.19 eV, and this small value is the origin of the high mobility of the TFT with amorphous InGaZnO₄.

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New As-based filled skutterudite compounds EuT₄As₁₂ (T=Fe, Ru, and Os) have been synthesized under high pressure; these compounds have lattice constants of 8.3374, 8.5120, and 8.5504 Å, respectively, which are larger than those expected from the lanthanide contraction in trivalent ions. The large lattice constants and effective magnetic moments (6.9–8.3 μ_B/Eu) of the compounds suggest that Eu ions in the compounds are in a divalent or mixed-valent state. Magnetic measurements reveal that EuFe₄As₁₂ and EuOs₄As₁₂ exhibit ferromagnetic-like phase transitions at 152 and 25 K, respectively. By contrast, EuRu₄As₁₂ shows no anomaly down to 2 K. The reciprocal susceptibility χ⁻¹ of EuFe₄As₁₂ has a nonlinear temperature dependence, which implies that the compound has a canted ferromagnetic or ferrimagnetic structure below 152 K. Furthermore, magnetization measurements of EuFe₄As₁₂ show that its magnetic moment is about 4.5 μ_B/Eu at 2 K, which is much less than the magnetic moment (7 μ_B/Eu) expected for Eu²⁺. The unexpectedly high transition temperature of 152 K in EuFe₄As₁₂ could be related to the interaction of Eu 4f moments with the ferromagnetic [Fe₄As₁₂] host lattice.

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We have studied the effect of magnetic rare-earth ion (Pr, Nd) doping on phase IV in Ce_xLa_1−xB₆ (x=0.4,0.5) systems. An unexpected large increase in the IV–I transition temperature T_IV–I by Pr and Nd dopings was observed, while no such increase was observed for x≥0.6. Although we do not know the reason why the doping effect markedly differs between x≤0.5 and x≥0.6 at present, the order parameter in phase IV for x≤0.5 is coupled with the magnetic dipole moment of Pr and Nd ions and phase IV is stabilized.

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We studied the current-induced magnetization dynamics of a domain wall pinned geometrically in a magnetic wire with bi-axial anisotropy. We showed that above the threshold current density, breathing-mode excitation, where the thickness of the domain wall oscillates, is induced by spin-transfer torque. We found that the breathing-mode can be applied as a source of microwave oscillation because the resistance of the domain wall is a function of the domain wall thickness. In a current sweep simulation, the frequency of the breathing-mode exhibits hysteresis due to the pinning.

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Quantum key distribution schemes which employ encoding on vacuum-one-photon qubits are capable of transferring more information bits per particle than the standard schemes employing polarization or phase coding. We calculate the maximum number of classical bits per particle that can be securely transferred when the key distribution is performed with the BB84 and B92 protocols, respectively, using the vacuum-one-photon qubits. In particular, we show that for a generalized B92 protocol with the vacuum-one-photon qubits, a maximum of two bits per particle can be securely transferred. We also demonstrate the advantage brought about by performing a generalized measurement that is optimized for unambiguous discrimination of the encoded states: the parameter range where the transfer of two bits per particle can be achieved is dramatically enhanced as compared to the corresponding parameter range of projective measurements.

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The dynamics of two-component Bose–Einstein condensates (BECs) in a double-well potential is studied here. Interspecies (or component–component) couplings are taken into account. As a consequence of the couplings, more fixed points may appear in the BECs. We analyze the stability of the system around some special fixed points that are independent of the couplings. A critical interspecies coupling constant below which fixed points are stable is presented and analyzed. Numerical simulation of the dynamics of the two-component BECs is also presented and discussed.

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We solve the time-dependent Schrödinger equation for the combination of a spin system interacting with a spin bath environment. In particular, we focus on the time development of the reduced density matrix of the spin system. Under normal circumstances we show that the environment drives the reduced density matrix to a fully decoherent state, and furthermore the diagonal elements of the reduced density matrix approach those expected for the system in the canonical ensemble. We show one exception to the normal case is if the spin system cannot exchange energy with the spin bath. Our demonstration does not rely on time-averaging of observables nor does it assume that the coupling between system and bath is weak. Our findings show that the canonical ensemble is a state that may result from pure quantum dynamics, suggesting that quantum mechanics may be regarded as the foundation of quantum statistical mechanics.

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We parallelize the density-matrix renormalization group method to directly extend it to two-dimensional (n-leg) quantum lattice models. The parallelization is performed mainly on the diagonalization for the superblock Hamiltonian since this step requires enormous memory space as the leg number n increases. The superblock Hamiltonian is divided into three parts, and the corresponding superblock vectors are transformed into matrices whose elements are uniformly distributed into processors. Parallel efficiency increases as the number of states kept, m, increases, and the obtained ground-state energy rapidly converges within a few sweeps. Furthermore, the present algorithm applied to doped 4-leg Hubbard ladders reaches their ground states, which satisfy the Lieb–Mattis theorem with m much smaller than those used in different indirect algorithms.

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We study population dynamics of a trapped spin-1 Bose gas above the Bose–Einstein transition temperature. Starting from the semiclassical kinetic equation for a spin-1 gas, we derive coupled rate equations for the populations of internal states. Solving the rate equations, we discuss the dynamical evolution of spin populations. We also estimate the characteristic timescale in which the system reaches equilibrium. Finally, we briefly discuss how the presence of the condensate will affect the population dynamics.

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We apply the direct method of obtaining reductions to the Toda hierarchy of equations. The resulting equations form a hierarchy of ordinary differential difference equations, also known as delay-differential equations. Such a hierarchy appears to be the first of its kind in the literature. All possible reductions, under certain assumptions, are obtained. The Lax pair associated to this reduced hierarchy is obtained.

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The molecular-crystal model, that describes a one-dimensional electron gas interacting with quartic anharmonic lattice vibrations, offers great potentials in the mapping of a relatively wide range of low-dimensional fermion systems coupled to optical phonons onto quantum liquids with retarded interactions. Following a non-perturbative approach involving non-Gaussian partial functional integrations of lattice degrees of freedom, the exact expression of the phonon-mediated two-electron action for this model is derived. With the help of Hubbard–Stratonovich transformation the charge-density-wave instability is examined in the sequel, with particular emphasis on the effect of the quartic anharmonic phonons on the charge-density-wave transition temperature.

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We consider a classical XY-like Hamiltonian on a body-centered tetragonal lattice, focusing on the role of interlayer frustration. A three-dimensional (3D) ordered phase is realized via thermal fluctuations, breaking the mirror-image reflection symmetry in addition to the XY symmetry. A heuristic field-theoretical model of the transition has a decoupled fixed point in the 3D XY universality, and our Monte Carlo simulation suggests that there is such a temperature region where long-wavelength fluctuations can be described by this fixed point. However, it is shown using scaling arguments that the decoupled fixed point is unstable against a fluctuation-induced biquadratic interaction, indicating that a crossover to nontrivial critical phenomena with different exponents appears as one approaches the critical point beyond the transient temperature region. This new scenario clearly contradicts the previous notion of the 3D XY universality.

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We construct a new multiconductor transmission-line theory with coefficients of potential and inductance. We provide coupled differential equations for potential and electric current with coefficients that are given by geometrical configurations of a transmission-line system. We provide a general solution to coupled differential equations explicitly for three-conductor transmission-lines. We derive coupled differential equations for the normal and common modes of lines 1 and 2, where common-mode current goes through line 3. The common mode acts as an antenna for radiating electromagnetic waves and any electromagnetic devices and conductors placed around the major conductor transmission-lines (lines 1 and 2) act as receivers of electromagnetic waves. This is the source of electromagnetic noise in the circumstance around the transmission-line system. The transmission-line system receives noise from the circumstance through the common mode.

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High-resolution atomic-beam ultraviolet (UV) laser spectroscopy in Ti I has been performed. Isotope shifts have been measured for seven UV transitions and hyperfine structure constants of ⁴⁷Ti and ⁴⁹Ti have been determined for five high-lying levels. Large specific mass shifts and significant field shifts have been derived for the studied transitions; the specific mass shift of the 3d²4s²–3d³4p transition is quite larger than that of the 3d²4s²–3d²4s4p transition. J dependences of isotope shift have been obtained for the 3d²4s4p ³F term and are mainly contributed from the specific mass shift.

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A simple method to control molecular translation with a chemical reaction is demonstrated. Slow NO molecules have been produced by partially canceling the molecular beam velocity of NO₂ with the recoil velocity of the NO photofragment. The NO₂ molecules were photodissociated using a UV laser pulse polarized parallel to the molecular beam. The spatial profiles of NO molecules showed two peaks corresponding to decelerated and accelerated molecules, in agreement with theoretical prediction. A significant portion of the decelerated NO molecules stayed around the initial dissociation positions even several hundred nanoseconds after their production.

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This paper clarifies quantitatively physical mechanisms of thermoacoustic Taconis oscillations in a helium-filled, quarter-wavelength tube by performing numerical simulations based on the one-dimensional nonlinear theory in the boundary-layer approximation developed in a previous paper. Thermoviscous effects appear in the form of memory integrals and affect the acoustic main-flow region through the radial velocity at the edge of the boundary layer. Solving an initial- and boundary-value problem for a smooth temperature distribution on the tube wall, it is revealed that the boundary layer in the cold part is active to pump energy into the main-flow region and the initial instability of the gas is brought about by a subtle unbalance in the axial distribution of net power input by the boundary layer. Also checked is the validity of Rayleigh’s criterion based on the heat flux into the gas through the tube wall. It is also revealed that Rayleigh’s criterion is similar to the present one based on the power input but it fails to pinpoint the instability.

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We have synthesized the polycrystalline Ba_1−xSr_xRuO₃ for 0≤x≤1.0, and investigated the crystal structure by X-ray powder diffraction. The crystalline structure of Ba_1−xSr_xRuO₃ of six-layer phase at around 0.4≤x≤0.8 is clarified to be six-layer monoclinic with C2⁄c symmetry. The high-temperature X-ray diffraction experiment revealed the structural transition between the six-layer monoclinic and six-layer hexagonal structure with P6₃⁄mmc around 580 K for x=0.5. For x=0.6 and 0.7, the monoclinic distortion decreases with increasing temperature though the transition was not observed below 623 K. The phase diagram of the crystalline structure against Sr content x of Ba_1−xSr_xRuO₃ at the ambient temperature and pressure was established in the present experiment as the nine-layer hexagonal for x=0, the four-layer hexagonal for 0.1≤x≤0.3, the six-layer monoclinic for 0.5≤x≤0.7 and perovskite for x=1.0. The crystal is the mixture of the six-layer monoclinic and the four-layer hexagonal at around x=0.4, and the mixture of the six-layer monoclinic and the perovskite at around 0.8≤x≤0.9. At the phase boundaries, the volume per formula unit and the averaged interlayer distance show a discontinuous decrease with increasing Sr content. However, the changes within the phase are much smaller than those at the phase boundaries.

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We study the ground state properties of the extended hard-core Bose–Hubbard model in a two-dimensional anisotropic triangular lattice by quantum Monte Carlo simulations. We present the ground state phase diagram at half filling. Four kinds of phases, including two solid phases, a superfluid phase and a supersolid phase, are observed. The supersolid phase exists only in a narrow region close to the isotropic limit. Away from half filling, we find that the results are strongly dependent on the phase at half filling. No supersolid phase exists if the ground state at half filling is a superfluid or a solid.

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NiGa₂S₄, FeGa₂S₄, and Fe₂Ga₂S₅ are layered triangular lattice antiferromagnets. Although the single-layer systems NiGa₂S₄ with S=1 and FeGa₂S₄ with S=2 are both insulators and have two-dimensional (2D) spin-disordered states, the bilayer system Fe₂Ga₂S₅, which has an effective buckled honeycomb lattice of S=2, is a semiconductor and exhibits an antiferromagnetic long-range order at 110 K. Here, we present our results of the resistivity measurements of single crystals of FeGa₂S₄ and Fe₂Ga₂S₅ under pressures of up to 8 GPa. We have observed a kink in the temperature dependence of the resistivity ρ(T) of FeGa₂S₄ under a pressure of 8 GPa, which is attributable to a transition from a 2D frozen spin-disordered state to a three-dimensional (3D) spin-ordered state. In either FeGa₂S₄ or Fe₂Ga₂S₅, we have observed no transition into a metallic state within pressure range of up to 8 GPa, despite the fact that the resistivities of both FeGa₂S₄ and Fe₂Ga₂S₅ show decreases with an increase in pressure at room temperature. The energy gap of FeGa₂S₄ estimated from the temperature dependences of the resistivities show negative pressure dependences.

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We calculate the electric conductance of a graphene nanoribbon (GNR) with and without a point defect. In the case of a zigzag GNR, magnetic moments are formed near the zigzag edges, and the electric current on each edge is spin-polarized. By breaking the symmetry of the magnetic moments with a single defect, such as a nonmagnetic vacancy, a net spin-polarized current can be generated in a zigzag GNR. The spatial distribution of the current is studied, and the spin-polarized current is found to arise owing to the blocking of a spin-polarized current-carrying mode by a vacancy.

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In studying current instabilities and chaos in semiconductor n-GaAs under weak photoexcitation, we pay special attention to influences from the carrier diffusion, arising from the space charges trapped near the injecting contacts. We extend the well-accepted two-impurity-level model by including the diffusion current δJ formed by such space charges near the negative contact. Without this δJ, one sees the prototype of period-doubling bifurcation (Feigenbaum scenario) but with unbound and exploding phenomena as the control parameter beyond 10.58 V/cm. Adding δJ in, we remove the unreasonable explosion and have the bifurcation routes to chaos of a current filament interrupted by a stable period 3 near E₀^[3]. Our simulations accurately reproduce the location of E₀^[3] and the Feigenbaum number. From our results, we see that δJ plays the role of providing strong friction and preventing the further increase of the conduction electron concentration from exploding.

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We study the conductance of a spinless non-interacting electron system consisting of randomly coupled N_R right-moving channels and N_L left-moving channels. This system serves as a model of disordered quantum wires with unitary symmetry. We focus on the case of N_R=1 with an arbitrary N_L. In this case, the dimensionless conductance g for the left-moving channels is by m≡N_L−1 greater than the dimensionless conductance g′ for the right-moving channels due to the presence of m perfectly conducting channels. That is, g=g′+m. Using a superspin approach, we obtain the average and second moment of g′ as a function of wire length L. The resulting asymptotic forms in the long-L regime are consistent with those obtained from the existing scaling theory.

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Heat capacities of halogen-bridged one-dimensional binuclear metal complexes (so-called MMX chain) having alkyl groups, Ni₂(RCS₂)₄I (R=Et and n-Pr), were measured by adiabatic and relaxation calorimetry. For each complex, a small broad thermal anomaly due to a spin-Peierls transition was observed around 40 K. For Ni₂(n-PrCS₂)₄I, a first-order phase transition was observed at 205.6 K. The enthalpy and entropy of transition were estimated to be about 4.05 kJ mol⁻¹ and 19.7 J K⁻¹ mol⁻¹, respectively. The magnitude of thermal anomaly shows that the effect of molecular dynamics of ligand on the electronic state in one-dimensional chain is small for Ni complexes having localized electrons in comparison with Pt complexes.

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The local electric properties of β-Ag_0.33V₂O₅, a pressure-induced superconductor, were studied at ambient pressure using a nuclear magnetic resonance (NMR) technique. Three crystallographically inequivalent Vi sites (i=1, 2, and 3) were identified from ⁵¹V-NMR spectra. We determined the principal axes of the electric-field-gradient (EFG) tensor, electric quadrupole frequency, asymmetric parameter, and Knight shift for each Vi site in the metallic phase and the subsequent charge-ordering (CO) phase at low temperatures. The results suggest that the electric properties for the V1 sites are similar to those for the V3 sites, whereas those for the V2 sites are different from those for the V1 and V3 sites. The peculiarity in the metallic phase reflects the electric properties in the CO phase and is attributable to the diagonal structure of the Vi orbitals.

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A pseudo honeycomb system Li₂RuO₃ exhibits a second-order-like transition at temperature T=T_c∼540 K to a low-T nonmagnetic phase with a significant lattice distortion forming Ru–Ru pairs. For this system, we have calculated the band structure, using the generalized gradient approximation (GGA) in both the high- and low-T phases, and found that the results of the calculation can naturally explain the insulating behavior observed in the low-T phase. The detailed characters of the Ru 4d t_2g bands obtained by the tight-binding fit to the calculated dispersion curves show clear evidence that the structural transition is driven by the formation of the Ru–Ru molecular orbit, as proposed in our previous experimental studies.

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Laser-driven molecular dissociation dynamics is investigated by conducting a simulation based on time-dependent density functional theory combined with molecular dynamics (TDDFT-MD). The conditions of the applied laser field (strength and frequency) required to dissociate a H₂ molecule are clarified. The photoabsorption spectra obtained have major peaks at the dissociation frequencies at which bonding (B) to antibonding (AB) electronic transitions occur. When a CH₄ molecule is irradiated by a laser field, only the CH bond parallel to the electric field is broken. We also found that laser-assisted hydrogen desorption crucially depends on the direction of the field relative to the CH₄ molecule as an adsorbate on the surface. The molecular processes of dissociation and desorption are clarified with the aid of the excited-state potential energy curves determined by TDDFT.

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Interplay of electron correlation and randomness is studied using the Anderson–Hubbard model within the Hartree–Fock (HF) approximation. Under the coexistence of short-range interaction and diagonal disorder, we obtain the ground-state phase diagram in three dimensions (3D), which includes an antiferromagnetic insulator, an antiferromagnetic metal, a paramagnetic insulator (Anderson-localized insulator), and a paramagnetic metal. Although only the short-range interaction is present in this model, we find unconventional soft gaps in the insulating phases irrespective of electron filling, spatial dimensions, and long-range order, where the single-particle density of states (DOS) vanishes with a power-law scaling in 1D or even faster in 2D and 3D toward the Fermi energy. We call such a gap a soft Hubbard gap. Moreover, exact-diagonalization results for 1D support the formation of a soft Hubbard gap beyond the mean-field level. The formation of the soft Hubbard gap cannot be attributed to the conventional theory by Efros and Shklovskii (ES) owing the emergence of soft gaps to the long-range Coulomb interaction. Indeed, on the basis of a multivalley energy landscape, we propose a phenomenological scaling theory, which predicts a scaling of the DOS, A in energy E as A(E)∝exp[−(−γlog|E−E_F|)^d]. Here, d is the spatial dimension, E_F is the Fermi energy, and γ is a non universal constant. This scaling is in perfect agreement with the numerical results. We further discuss a correction of the scaling of the DOS by the long-range part of the Coulomb interaction, which modifies the ES scaling. Furthermore, explicit formulae for the temperature dependence of the DC resistivity via variable-range hopping under the influence of the soft gaps are derived. Finally, we compare the present theory with experimental results for SrRu_1−xTi_xO₃.

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We have performed a systematic tight-binding analysis of the angle-resolved photoemission spectroscopy (ARPES) spectra of a series of transition-metal (TM) oxides A(TM)O₃ and compared the obtained electronic structure parameters with those well established values obtained from cluster-model analyses of photoemission spectra. The values of ε_d−ε_p from ARPES are found to be much larger than the values which would be expected for the limit of weak p–d hybridization, indicating that the “effective” TM 3d bands are originated from the strong hybridization with the O 2p bands even for light TM oxides.

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In order to clarify the adsorption mechanism of the O₂ molecule on Co–polypyrrole composite metallo-organic catalyst, we have investigated the interaction between the molecule and Co–(n)pyrrole model clusters (n=4,6) using the density functional theory. The stable adsorption site of the O₂ molecule on Co–(4)pyrrole is found to be at the O–O center of mass located on top of the Co atom in side-on configuration, while for the case of Co–(6)pyrrole cluster, the O₂ molecule is slightly deviated from the side-on configuration. The O–O bonds of the O₂/Co–(4)pyrrole and the O₂/Co–(6)pyrrole systems have elongated by 10.84 and 9.86%, respectively. The elongation mechanism of O₂ on Co–(n)pyrrole is induced by the interaction between the cobalt d-orbitals and the O₂ anti-bonding π^* orbital, which results in a charge transfer from the cobalt atom toward the O₂ molecule. This effect seems important in the adsorption of the O₂ molecule on Co–(n)pyrrole. It is likely that the extra charge in the O₂ molecule would fill its anti-bonding orbital and consequently weaken the O–O bond. In Co–(4)pyrrole, the elongation of the O₂ bond is larger than that of Co–(6)pyrrole since a complete side-on configuration has more symmetric overlapping between the cobalt d-orbitals and the O₂ anti-bonding orbital.

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We have measured and analysed the magnetization, resistivity and thermopower of polycrystalline samples of Ca-subsituted Sr₃YCo₄O_10.5. While the transition temperature and thermopower systematically decrease with increasing Ca content, the resistivity is nearly independent of the Ca-substitution level. We have furhter found that the substitution of Ca for Sr systematically decreases the lattice paremeters while maintaining the oxygen content unchanged, and have explained the Ca-substitution effects in terms of the spin-state transition induced by chemical pressure. We have also measured the magnetization of one of the samples under hydrostatic pressure. The result shows that the physical-pressure effect is semiquantitatively consistent with the chemical-pressure effect.

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The gap equation for anisotropic superconductivity is solved in the presence of elastic scatterings by nonmagnetic and magnetic impurities, which are treated by the self-consistent Born approximation, and inelastic scatterings, which are phenomenologically treated. When elastic scatterings are strong, even at T=0 K, coherence peaks almost disappear and the gap is a pseudogap, i.e., the density of states ρ(ε) is nonzero at the chemical potential, which means that the T-linear specific heat coefficient is nonzero in the superconducting state. At T=0 K in such a case, the low-energy part of ρ(ε) or the gap spectrum has a concave-cap V shape, which is in contrast to a convex-cup V shape in the absence of scattering. When elastic or inelastic scatterings are strong, the ratio ε_G(0)⁄k_BT_c is much larger than its mean-field value of about 4, where ε_G(0) is the gap at T=0 K and T_c is the superconducting critical temperature. The large ε_G(0)⁄k_BT_c\\simeq8 and the linear decrease in T_c in residual resistivity, both of which are observed in cuprate superconductors and the latter of which is inconsistent with the Abrikosov and Gor’kov theory, can be explained by the temperature-dependent pair breaking estimated from the T-linear coefficient of resistivity, which is about 1 μΩ cm/K.

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Field-oriented anisotropy of specific heat and magnetization in PrOs₄Sb₁₂ is discussed on the basis of the generalized Holstein–Primakoff formalism under magnetic fields. With a moderate amount of the mixing parameter characterizing T_h symmetry, we obtain distinct anisotropy of the specific heat due to fluctuations for H||[100] and H||[110] both in the para and the antiferro-quadrupole phases. Tendency of the anisotropy in the specific heat is consistent with the experimental results, while the calculated anisotropy of the magnetization in the para phase is opposite to that observed in the experiment. Although the magnetic field usually suppresses fluctuations due to level splitting, the presence of the critical soft modes in the exciton dispersion contributes significantly to thermodynamic quantities in antiferro-quadrupole systems.

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The weak-field Hall conductivity is calculated in monolayer graphene within a self-consistent Born approximation. The Hall conductivity sufficiently away from the Dirac point exhibits the dependence qualitatively in agreement with the Boltzmann result, but it deviates in the region near zero energy, the width of which is singularly dependent on the scattering strength. The experimental results can be reasonably well understood by assuming that the scattering strength increases with the decrease of the electron concentration and saturates in this region.

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Characterization of the interaction between vacancy defects in zigzag single-walled carbon nanotubes (SWCNTs) was carried out through geometric and bandstructure analyses with density functional theory (DFT). This interaction depends on the detail orientation between the defects and, in turns, influences the electric properties of the defective zigzag SWCNTs if any two defects are within the defect influencing range. Our results shed some light on the origin of the instability found in the electric properties of SWCNTs.

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The applied field dependence of the depth distribution of Au spin polarization is investigated for an epitaxial Fe/Au(001) multilayer with antiferromagnetic interlayer coupling by resonant X-ray magnetic diffraction using circularly polarized synchrotron X-rays near the Au L₃ absorption edge. The magnetic Bragg intensities of the multilayer are measured up to the fifth order with varying the applied field between ±500 Oe. All magnetic diffraction intensities are found to be proportional to the Fe layer magnetization at the same applied field. This result indicates that the size of the induced Au spin polarization parallel to the applied field direction is proportional to the Fe layer magnetization and that the depth distribution of the induced Au spin polarization scaled to the Fe layer magnetization is unchanged during the magnetization process of the antiferromagnetically coupled Fe layers.

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We report the x-ray absorption near edge structure at the Ce L₃ edge for amorphous alloys Ce_xRu_100−x (x=9, 43, and 80) and a C15 Laves phase compound CeRu₂, which consists of a couple of peaks characteristic of 4f¹ and 4f⁰ configurations. This indicates that Ce atoms of these materials are in a mixed valence state. The spectra are fitted to one arctangent and two Lorentzian functions. The Ce valence estimated from relative areas of the Lorentzian peaks varies linearly with Ce content. The transition into the continuum along with both peaks shifts to lower energy with increasing Ce concentration. We find a linear relation between the transition energy and the valence.

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Recently reported inverse isotope effect is investigated on the basis of the two-band and two-channel attractive model by using the weak coupling Bardeen–Cooper–Schrieffer (BCS) scheme. If we assume the several attractive or repulsive interactions for Cooper pairs, which works in different energy ranges, the isotope exponent α takes values even in the range of α<0 (negative) and α>0.5, depending on the strength and the range of interactions. We apply the theory to recently observed remarkable inverse isotope effect α≈−0.18 for the Fe-pnictide (Ba,K)Fe₂As₂ superconductor. The large inverse isotope effect naturally originates from the competition between the magnetically induced pair interaction and the inter-band electron–phonon coupling. It evidently indicates that the superconductivity in Fe pnictides arises from the magnetically induced attractive interaction.

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