[en] The authors studied the low-temperature energy gap 2Δ_o on Bi₂Sr₂CaCu₂O₈+delta (Bi2212) and La_2-xSr_xCuO₄ (La214) systematically over a wide range of doping level p using STS, break junction tunneling spectroscopy, Raman scattering and low-T electronic specific heat data. They have also studied the electronic specific heat of La214 in the normal state at T > Tc, and confirmed that pseudogap behavior appears at around T*, below which the in-plane resistivity ρ and magnetic susceptibility χ tend to be slightly suppressed. Similar suppression appears in ρ and χ of Bi2212 below the onset temperature of pseudogap T*. It is pointed out in the present study that 2Δ_o is closely related to T* in both Bi2212 and La214 systems; T* approximately 2Δ_o/4.3 k_B. It is also pointed out that 2Δ_o is in almost linear proportion to k_BT_max(much_ltT*), where T_max is the temperature exhibiting a broad peak in χ-T curves and k_BT_max can be considered to give a measure of the effective antiferromagnetic exchange energy J_eff. The α factors in 2Δ_o approximately αk_BT_max approximately αJ_eff are approximately 1 for La214 and approximately 2 for Bi2212, respectively. They also report that in both Bi2212 and La214 systems Tc roughly scales with pΔ_o except in highly doped samples, where Tc ∝ 2Δ_o

[en] In La214, the electronic specific heat coefficient γ (=C_el/T) is gradually suppressed with lowering T below a certain temperature T*(> Tc), where the in-plane resistivity ρ and magnetic susceptibility χ also tend to be suppressed slightly. Temperature T*, increasing with lowering x, is in qualitative agreement with the mean field Tc(T_co), estimated from the superconducting gap amplitude 2Δ_o at T much_lt Tc, as the onset temperature T* of a pseudogap in Bi2212. The gradual suppression of γ below approximately T_co implies that a pseudogap will also open up below approximately T_co in La214 as in Bi2212. In underdoped samples, whose pseudogap-like behaviors in C_el(T) become marked, the anomaly of C_el around Tc is rather different from the BCS expectation

[en] The nonlinear conductivity in the charge-density-wave states in NbSe³ was measured up to the high-field limit. Ohmicity recurs in this limit. The temperature dependence of σsub(eo), the extra conductivity in the high-field limit, is in agreement with that of carrier concentration condensed into the CDW, providing an evidence that the nonlinear conductivity is due to CDW motion. The magnitude of σsub(eo) is very sensitive to the impurity concentration. The mobility of the drifting CDW's is temperature independent and the damping of them is mainly due to the impurity scattering in even pure crystals. (author)

[en] Detailed resistivity measurements and X-ray and microscopic examinations revealed that pure NbSe³ does not show superconductivity at least above 0.38K at ambient pressure. The superconductivity with the sluggish, current-sensitive transition curve, which has been observed frequently, is extrinsic and arises only from the crystal boundaries in the polycrystalline sample. (author)

[en] Superconducting gap magnitude 2Δ_o is re-examined by STM/STS at T << Tc in Bi2212. It is confirmed that 2Δ_o increases monotonically with lowering the doping level p and almost scales with pseudogap temperature T* over the entire p range examined; 2 Δ_o(p)approximately4.3k_BT*(p). Furthermore, it is shown that Tc is almost given by renormalizing 2Δ_o or T* with p; k_BTc(p)∝pΔ_o(p) or Tc(p)∝pT*(p)

[en] In La_2-xBa_xCuO₄ (LBCO) and La_1.8-xNd_0.2Ba_xCuO₄ (LNBCO), the low-temperature structural change at T₁ (= 60-110 K), resulting from tilt of the CuO₆ octahedra, is easily suppressed at high pressures. However, the structural change of LNBCO (x=0.125) remains up to 2GPa though it jumps from T₁ (∼110K) to T* (∼60K), where the electric resistivity ρ begins to upturn, at 0-1.5 GPa. The upturn of ρ is also suppressed at high pressures, and the superconducting critical temperature T_c is fully restored except in a very narrow x-range around x=0.125. The T_c for x ∼ 0.125 is appreciably lower at 2GPa than those for other Ba-contents

[en] TaS₃ exhibits the metal-semiconductor transition at 218 K due to the Peierls instability. The electrical resistance was measured under pressure. It was found that both the transition temperature, Tsub(p), and the activation energy at T = 0 K, Δ(0), decrease with pressure, while the ratio, Δ(0)/Tsub(p), is independent of pressure. (author)

[en] Clear atomic images of Bi₂Sr₂CaCu₂O_8+δ cleaved surfaces have been observed at T=6 and 300 K by scanning tunneling microscopy (STM). The atomic images taken for bias voltages much lower than the Bi-O plane semiconducting gap E_g∼100 meV, corresponding to the Cu-O plane, indicate that the conduction electrons exist mainly in the Cu 3d_x²-y² and O 2p_σ orbitals. Tunneling spectra have been also measured in the same processes as in the Cu-O plane STM image observations at T=6 K. The low-temperature spectra are in good agreement with that in a d-wave superconductor with an anisotropic Fermi surface on which the normal density of states N(k_F) is largest (N_max) for the maximum gap directions and decreases to ∼N_max/2 for the node directions. This, combined with the result on the N(k_F) anisotropy in photoemission experiments, is consistent with a d_x²-y² superconducting gap. copyright 1996 The American Physical Society

[en] We present an inelastic neutron scattering study of the spin dynamics in the mixed phase of the high-T_c superconductor La_2-xSr_xCuO₄. In the overdoped regime (x=0.17, T_c=37 K) the application of a magnetic field induces a spectral weight redistribution centered around the zero-field spin gap (Δ_SG∼6.5 meV). Moreover the opening of the spin gap seems to track the irreversibility temperature (related to the melting of the vortex lattice) rather than T_c, indicating an unusual interplay between the mesoscopic and microscopic properties in La_2-xSr_xCuO₄. In the underdoped regime (x=0.10, T_c=29 K) our zero-field data indicate a strong decrease (or even vanishing) of the spin gap in the superconducting state and no dependence upon the application of a magnetic field

[en] Since the publication of JAERI-1285 in 1983 for the preliminary version of the SRAC code system, a number of additions and modifications to the functions have been made to establish an overall neutronics code system. Major points are (1) addition of JENDL-2 version of data library, (2) a direct treatment of doubly heterogeneous effect on resonance absorption, (3) a generalized Dancoff factor, (4) a cell calculation based on the fixed boundary source problem, (5) the corresponding edit required for experimental analysis and reactor design, (6) a perturbation theory calculation for reactivity change, (7) an auxiliary code for core burnup and fuel management, etc. (author)