H. Yamaguchi

Angular position of nodes in the superconducting gap of quasi-2D heavy-fermion superconductor CeCoIn5.

The thermal conductivity of the heavy-fermion superconductor CeCoIn5 has been studied in a magnetic field rotating within the 2D planes. A clear fourfold symmetry of the thermal conductivity which is characteristic of a superconducting gap with nodes along the ( +/- pi,+/- pi) directions is resolved. The thermal conductivity measurement also reveals a first-order transition at H(c2), indicating a Pauli limited superconducting state. These results indicate that the symmetry most likely belongs to d(x(2)-y(2)), implying that the anisotropic antiferromagnetic fluctuation is relevant to the superconductivity.

Superconducting Gap Structure of κ − ( BEDT − TTF ) 2 Cu ( NCS ) 2 Probed by Thermal Conductivity Tensor

The thermal conductivity of organic superconductor kappa-(BEDT-TTF)2Cu(NCS)2 (Tc = 10.4 K) has been studied in a magnetic field rotating within the 2D superconducting planes with high alignment precision. At low temperatures ( T < or = 0.5 K), a clear fourfold symmetry in the angular variation, which is characteristic of a d-wave superconducting gap with nodes along the directions rotated 45 degrees relative to the b and c axes of the crystal, was resolved. The determined nodal structure is inconsistent with recent theoretical predictions of superconductivity induced by the antiferromagnetic spin fluctuation.

Superconducting Gap Structure of Spin-Triplet Superconductor Sr2RuO4 Studied by Thermal Conductivity

To clarify the superconducting gap structure of the spin-triplet superconductor Sr2RuO4, the in-plane thermal conductivity has been measured as a function of relative orientations of the thermal flow, the crystal axes, and a magnetic field rotating within the 2D RuO2 planes. The in-plane variation of the thermal conductivity is incompatible with any model with line nodes vertical to the 2D planes and indicates the existence of horizontal nodes. These results place strong constraints on models that attempt to explain the mechanism of the triplet superconductivity.

Superconducting Gap Structure ofκ−(BEDT−TTF)2Cu(NCS)2Probed by Thermal Conductivity Tensor

The thermal conductivity of organic superconductor kappa-(BEDT-TTF)2Cu(NCS)2 (Tc = 10.4 K) has been studied in a magnetic field rotating within the 2D superconducting planes with high alignment precision. At low temperatures ( T < or = 0.5 K), a clear fourfold symmetry in the angular variation, which is characteristic of a d-wave superconducting gap with nodes along the directions rotated 45 degrees relative to the b and c axes of the crystal, was resolved. The determined nodal structure is inconsistent with recent theoretical predictions of superconductivity induced by the antiferromagnetic spin fluctuation.

Structural Evolution in the Neutron-Rich Nuclei ^{106}Zr and ^{108}Zr

The low-lying states in ¹⁰⁶Zr and ¹⁰⁸Zr have been investigated by means of β-γ and isomer spectroscopy at the radioactive isotope beam factory (RIBF), respectively. A new isomer with a half-life of 620 ± 150 ns has been identified in ¹⁰⁸Zr. For the sequence of even-even Zr isotopes, the excitation energies of the first 2⁺ states reach a minimum at N = 64 and gradually increase as the neutron number increases up to N = 68, suggesting a deformed subshell closure at N = 64. The deformed ground state of ¹⁰⁸Zr indicates that a spherical subshell gap predicted at N = 70 is not large enough to change the ground state of ¹⁰⁸Zr to the spherical shape. The possibility of a tetrahedral shape isomer in ¹⁰⁸Zr is also discussed.

Angular position of nodes in the superconducting gap of 2D unconventional superconductors

Abstract The superconducting gap structure, especially the direction of the nodes, is an unresolved issue in most of unconventional superconductors. Here, we have measured the thermal conductivity of 2D unconventional superconductors, spin-triplet Sr 2 RuO 4 and heavy fermion CeCoIn 5 , in magnetic field rotating within the planes. On the basis of the angular variation of the thermal conductivity, we demonstrate that the gap function of Sr 2 RuO 4 is d ( k )=Δ 0 z (k x + i k y )( cos ck z +α) , and the gap function of CeCoIn 5 is d x 2 − y 2 .

Gap structure and anomalous superconducting state of quasi-2D heavy-fermion CeCoIn5

Abstract To specify the direction of the nodes in the superconducting gap, we measured the thermal conductivity κ of quasi-2D heavy-fermion CeCoIn5 in a magnetic field rotating within the 2D planes. A clear fourfold symmetry of κ which is characteristic of a superconducting gap with nodes along the (±π,±π)-directions is resolved. The thermal conductivity also reveals a first order phase transition at Hc2. The results indicate that the symmetry most likely belongs to dx2−y2, implying that the anisotropic antiferromagnetic fluctuation is relevant to the superconductivity.

Probing the nodal structure in quasi-2D unconventional superconductors by thermal conductivity

The superconducting gap structure is an unresolved issue in most of unconventional superconductors. Here we measured the thermal conductivity of 2D unconventional superconductors, spin-triplet Sr 2 RuO 4 , heavy fermion CeCoIn 5 and organic κ-(BEDT-TTF) 2 Cu(NCS) 2 , in magnetic field rotating within the 2D planes. On the basis of the angular variation in the thermal conductivity, we demonstrate that the gap function is d(k) = Δ 0 Z(k x + ik y )(cos ck z + a) for Sr 2 RuO 4 , d x 2 -y 2 for CeCoIn 5 , and d xy for κ-(BEDT-TTF) 2 Cu(NCS) 2 .

Search for spin-orbit-force reduction at 106,108Zr around r-process path

Shell gap at the magic number N = 82 is important to reproduce the 2nd peak of r-process abundance. If a spin-orbit force is reduced in a very neutron-rich region, a shell quenching at N = 82 and a new shell closure at N = 70 are predicted. A shell evolution by the spin-orbit-force reduction can be searched for through the shape evolution of Zr isotopes around an expected double magic nuclei, 110Zr(Zu2009=u200940,Nu2009=u200970). We performed β-γ and isomer spectroscopy at RIBF to observe low-lying states in 106,108Zr. The present results indicate a well deformed shape for 106,108Zr. The drastic reduction of the spin-orbit force most likely does not occur around 110Zr on an r-process path.