Experimental Evidence for Spin-Triplet Superconductivity in Sr2RuO4

We review the experimental evidence for spin-triplet superconductivity in Sr₂RuO₄. The Knight shift experiments decisively demonstrated that the Cooper-pair symmetry is spin triplet. We discuss the most probable wave function of the Cooper pairs on the basis of the results of a number of key experiments. We point out that a simple picture of the unitary state with the isotropic gap is not compatible with the observed behavior of the specific heat, and that a profound modification of the pairing wave function is needed. We also present the in-plane angular dependence of the upper critical field, with the field applied exactly parallel to the quasi-two-dimensional plane. We discuss the possible implication of the observed fourfold anisotropy in connection with the proposed second superconducting state with a line-node gap.     

The Unconventional Superconductivity of Sr2RuO4

We review the evidence for unconventional superconductivity in Sr ₂ RuO ₄ ; the pairing in this material is certainly non-s-wave, and most of the current observations can be accounted for by a particular p-wave state, which is doubly degenerate and breaks time-reversal symmetry. Our observations of the flux lattice by small-angle neutron scattering contribute to this picture. The square flux lattice and the intensity of the diffracted signal indicate that superconductivity resides primarily on the sheet of the Fermi surface, which is derived from the Ru - d _xy orbitals. This is in agreement with the orbital-dependent p-wave scenario. Furthermore, the shape of the flux lines derived from these measurements is strongly indicative of a two-component order parameter.     

Effect of Impurities on the Specific Heat of the Spin-Triplet Superconductor Sr2RuO4

We have investigated the specific heat of single crystals of the spin-triplet superconductor Sr ₂ RuO ₄ (T _c0 = 1.50 K) with various T _c . We focus on the T _c dependence of the specific heat jump at T _c and of the residual specific heat coefficient. The observed behavior is not quantitatively consistent with a model with a simple isotropic gap. We argue that inclusions of both the in-plane anisotropy of the gap and the dependence of the gap on different Fermi-surface sheets are needed to resolve this discrepancy.     

Theoretical Consideration on Triplet Superconductivity in UPt3 and Sr2RuO4

Two representative superconductors, UPt₃ and Sr₂RuO₄, are comparatively studied on the basis of a general symmetry argument. The existing experimental data set for both systems strongly and commonly points to a triplet pairing. For the former, heavy fermion material, UPt₃, a non-unitary bipolar state is the most possible candidate, whereas for the latter system, Sr₂RuO₄, determination of a precise pairing symmetry class, either unitary or non-unitary, is debated.     

The Specific Heat and the Fermi Surface Anisotropy in Sr2RuO4

The influence of the Fermi surface anisotropy on the specific heat jump is studied for the p-wave superconductor with a gap function d = z^(k _x ± ik _y ) in connection with Sr₂RuO₄. It is shown that the normalized specific heat jump, C/T _c , is reduced from its universal value, 1.43, in accordance with experimental findings. We show that this behavior fits well into our present understanding of the quasiparticle spectrum and the impurity effects.     

p-Wave Superconductors in Sr2RuO4 and Bechgaard Salts

We review our recent works on the vortex state in p-wave superconductors. First, in a magnetic field parallel to the c-axis, the square vortex lattice is most stable, except in the immediate vicinity of T = T _c0. Second, the effect of impurities on H _c2 is studied, which exhibits characteristics of unconventional superconductors. Finally, the a–b anisotropy in the upper critical field in a magnetic field is considered. This anisotropy provides important information about the fourfold term arising from the Fermi surface effect.     

Theory of Josephson Effect in Sr2RuO4/Diffusive Ferromagnet/Sr2RuO4 Junctions

We study Josephson effect in Sr₂RuO₄/insulator/diffusive ferromagnet (DF)/insulator/Sr₂RuO₄ junctions, solving the Usadel equation under a new boundary condition for DF/Sr₂RuO₄ interface. Josephson current is calculated changing temperatures, resistances of the interfaces between the DF and Sr₂RuO₄, the exchange field in the DF, and a length of the DF. We find that the exchange field can induce the 0–π transition in these junctions.     

Point-Contact Spectroscopy on Sr2RuO4

We report on point-contact spectroscopy experiments on superconducting Sr ₂ RuO ₄ . For current injection into the ab-plane two distinctly different types of spectra are observed, one with a double-minimum structure and one with a zero-bias anomaly which gives evidence for unconventional pairing in this system. For current injection into the c-direction non-spectroscopic effects are dominant.     

Calorimetric and transport properties of Zircalloy 2, Zircalloy 4, and Inconel 625

This paper presents the measurements and the results on thermal and electrical transport properties of three nuclear reactor cladding materials: Zircalloy 2, Zircalloy 4, and Inconel 625. Study of these materials constituted a part of the IAEA coordinated research program aimed at the generation and establishment of a reliable and complete database of the thermal properties of reactor materials. Measured properties include thermal diffusivity, specific heat, and electrical resistivity. Thermal diffusivity was measured by the laser pulse technique. Specific heat and electrical resistivity were measured using a millisecond-resolution direct electrical pulse heating technique. Thermal conductivity was computed from the experimentally determined thermal difusivity and specific heat functions and the room temperature density values. Measurements were performed in the 20 to 1500°C temperature range, depending on the material and property concerned.     

Charge Stripes and Superconductivity in La2−x Ba x CuO4 and La1.6−x Nd0.4Sr x CuO4

We report x-ray scattering study of charge density wave (stripe) order in La_2−x Ba _x CuO₄ (LBCO) and La_1.6−x Nd_0.4Sr _x CuO₄ (LNSCO). The doping dependence of the charge stripe ordering temperature and the low-temperature correlation length is compared with the bulk superconducting transition temperature. We find that the charge stripe ordering temperature and correlation length are quite different in these two families of cuprates, while there seems to be inverse correlation between the bulk superconducting temperature and the charge stripe correlation length.     

Specific Heat of CeRhIn5: Pressure-Driven Transition from Antiferromagnetism to Heavy-Fermion Superconductivity

CeRhIn₅ is known to show an unusual transition at a critical pressure of 15 kbar. Specific-heat data show a gradual change in the zero-field magnetic specific-heat anomaly from one typical of antiferromagnetic ordering at ambient pressure to one more characteristic of a Kondo singlet ground state at 21 kbar. However, at 15 kbar there is a discontinuous change from an antiferromagnetic ground state to a superconducting ground state, and evidence of a weak thermodynamic first-order transition. Above the critical pressure, the low-energy excitations are characteristic of superconductivity with line nodes in the energy gap, and, at intermediate pressures, of extended gaplessness.     

Simultaneous measurements of thermal conductivity and diffusivity of Se80Te20-xInx (x = 2, 4, 6 and 10) chalcogenide glasses at room temperature

Measurements of thermal conductivity and thermal diffusivity of twin pellets of Se₈₀Te_20-xIn_x (x = 2, 4, 6 and 10) glasses, prepared under a load of 5 tons were carried out at room temperature using transient plane source (TPS) technique. The measured values of both thermal conductivity and diffusivity were used to determine the specific heat per unit volume of the said materials in the composition range of investigation. Results indicated that both the values of thermal conductivity and thermal diffusivity increased with the addition of indium at the cost of tellurium whereas the specific heat remained almost constant. This compositional dependence behaviour of the thermal conductivity and diffusivity has been explained in terms of the iono-covalent type of bond which In makes with Se as it is incorporated in the Se-Te glass.     

Normal-state and superconducting properties of Sr2RuO4

We discuss some of the current issues on the copper-free layered perovskite superconductor Sr₂RuO₄, for which a sharp transition at T_c = 1.2 K has been reproducibly obtained. The normal state is characterized as an essentially twodimensional Fermi liquid, and the coherent interlayer transport is established only at low temperatures. The cylindrical Fermi surface observed by de Haas-van Alphen experiments is consistent with other thermodynamic and transport properties. Although the specific heat jump across T_cconfirms the bulk superconductivity, the large residual T-linear term which correlates with the variation in T_cis unusual and suggestive of unconventional pairing.On leave from Hiroshima University.     

Ferromagnetic Correlations in Ca-Doped Sr2RuO4: 87Sr NMR Study

Magnetic properties on Sr_2–x Ca _x RuO₄ have been investigated by a microscopic probe of ⁸⁷Sr-NMR in order to understand the magnetic character on spin-triplet superconductor of Sr₂RuO₄, which has multibands on the Fermi surface. With substituting Ca for Sr which gives rise to crystal distortion, the Knight shift (K) and the nuclear spin-lattice relaxation rate divided by temperature (1/T _{1 T}) increases progressively up to x=1.5. The Korringa relation from K and 1/T ₁ T becomes smaller, indicative of development of ferromagnetic fluctuations with increasing Ca content. This suggests that the q-independent spin fluctuations originating from the 2-dimensional band are changed to the ferromagnetic ones by the Ca doping.     

LCAO analysis of Sr2RuO4 band structure

A simple tight-binding model for the conduction band of Sr₂Ru0₄ is presented. The Ru4d and 02p orbitals of RuU₂ conduction plane are taken into account. In momentum representation the LCAO Hamiltonian has a block structure, containing hopping amplitudes between the in-plane orbitals O_a2p_y, O_b2p_x, Ru4d_xy, and those vertical to RuO₂ plane — Ru4d_yz, Ru4d_zx, O_a2_pz and O_b2_pz. This simple structure allows an analytical derivation of electron band dispersions (p_x,P_y) and constant energy contours (p_x,p_y) = const. The energy surfaces (p_x,P_y) (numerically calculated) are also related to angle-resolved photoemission spectra. Based on the analytical results a fitting philosophy for both the available experimental data and ab initio calculations is discussed. The tight-binding parameters calculated within the adopted model are found to be in acceptable agreement with the first principles calculations.     

Possible Superconductivity in TiSe2 Intercalated by Transition Metals

Electric conductivity and magnetoresistence data for TiSe₂ intercalated by Fe²⁺ and Cr³⁺ are interpreted as superconducting state with T _c ∼ 5 and 4 K, respectively.     

Electronic Theory for the Magnetic Anisotropy in Sr2RuO4

Using a three-band Hubbard Hamiltonian we calculated within the random-phase-approximation the spin susceptibility, χ(q, ω), and NMR spin-lattice relaxation rate 1/T ₁, in the normal state of the triplet superconductor Sr₂RuO₄, and obtained quantitative agreement with experimental data. Most importantly, we found that because of spin–orbit coupling the out-of-plane component of the spin susceptibility χ ^zz (q, ω) becomes two times larger than the in-plane one at low temperatures. We analyze in particular the role of the xy-band in the magnetic anisotropy.     

Li2B4O7晶体的比热,导温和导热性能

用ＤＳＣ和激光热导人义分别测定了Ｌｉ２Ｂ４Ｏ７（ＬＢＯ）晶体３５０－９７０Ｋ范围内的比热和６３０－９７０Ｋ范围内不同主晶轴方向的导温系数，并由此了导热系数和声子平均自由程。