D. Matsuda Tatsuma

Unconventional Heavy-Fermion Superconductivity of a New Transuranium Compound NpPd5Al2

We succeeded in growing a new transuranium compound NpPd 5 Al 2 with the tetragonal crystal structure by the Pb-flux method, and measured the electrical resistivity, specific heat, magnetic susceptibility and magnetization. NpPd 5 Al 2 is found to be a paramagnetic heavy-fermion superconductor with strong coupling Δ C /γ T c = 2.33 [ T c =4.9 K and γ= 200 mJ/(K 2 ·mol)]. The upper critical field H c2 at 0 K is large and highly anisotropic: H c2 (0) =37 kOe for H ∥[100] and H c2 (0) =143 kOe for H ∥[001]. H c2 is found to be strongly suppressed by the magnetic field, and the magnetization curve indicates a step-like increase at H c2 , which are due to the paramagnetic effect. The low-temperature electronic specific heat approximately follows the T 3 -dependence, indicating the existence of point nodes in the energy gap. The d -wave superconductivity with point nodes is most likely realized in this compound.

Anisotropic Superconducting Gap in Transuranium Superconductor PuRhGa5: Ga NQR Study on a Single Crystal

69,71 Ga NMR/NQR studies have been performed on a single crystal of the transuranium superconductor PuRhGa 5 with T c ≃9 K. We have observed a 69 Ga NQR line at ∼29.15 MHz, and assigned it to the 4 i Ga site using the NMR results. The 69 Ga NQR spin–lattice relaxation rate 1/ T 1 shows no coherence peak just below T c , but obeys T 3 behavior below T c . This result strongly suggests that PuRhGa 5 is an unconventional superconductor having an anisotropic superconducting gap. The gap amplitude 2Δ 0 ( T →0)≃5 k B T c and the residual density of states N res ( T =0)/ N 0 ( T = T c )≃0.25 have been determined assuming a simple polar function of the form Δ(θ,φ)=Δ 0 cos θ, where θ and φ are angular parameters on the Fermi surface.

Ferromagnetic Quantum Critical Endpoint in UCoAl

Resistivity and magnetostriction measurements were performed at high magnetic fields and under pressure on UCoAl. At ambient pressure, the 1st order metamagnetic transition at H_m ~ 0.7 T from the paramagnetic ground state to the field-induced ferromagnetic state changes to a crossover at finite temperature T_0 ~11 K. With increasing pressure, H_m linearly increases, while T_0 decreases and is suppressed at the quantum critical endpoint (QCEP, P_QCEP ~ 1.5 GPa, H_m ~ 7 T). At higher pressure, the value of H_m identified as a crossover continuously increases, while a new anomaly appears above P_QCEP at higher field H* in resistivity measurements. The field dependence of the effective mass (m*) obtained by resistivity and specific heat measurements exhibits a step-like drop at H_m at ambient pressure. With increasing pressure, it gradually changes into a peak structure and a sharp enhancement of m* is observed near the QCEP. Above P_QCEP, the enhancement of m* is reduced, and a broad plateau is found between H_m and H*. We compare our results on UCoAl with those of the ferromagnetic superconductor UGe2 and the itinerant metamagnetic ruthenate Sr3Ru2O7.

Magnetic and Superconducting Properties of CeTX3 (T: Transition Metal and X: Si and Ge) with Non-centrosymmetric Crystal Structure

We grew single crystals of non-centrosymmetric compounds CeTSi 3 and CeTGe 3 (T: transition metal), and studied the magnetic properties by measuring the electrical resistivity, magnetic susceptibility and magnetization. We also studied the effect of pressure on the electronic states in antiferromagnets CeTGe 3 (T: Co, Rh, Ir) by measuring the resistivity under pressure. No noticeable change of the Neel temperature was observed up to 8 GPa in CeRhGe 3 and CeIrGe 3 , which are far from the magnetic quantum critical point. On the other hand, the Neel temperature in CeCoGe 3 was strongly decreased as a function of pressure, and pressure-induced superconductivity was observed in the pressure region from 5.4 GPa to about 7.5 GPa. The slope of upper critical field H c2 at 6.5 GPa is found to be extremely large, with an upturn curvature of H c2 with decreasing temperature: -d H c2 /d T = 200 kOe/K at the superconducting transition temperature T sc = 0.69 K, revealing unconventional superconductivity.

Evidence for Novel Pairing State in Noncentrosymmetric Superconductor CePt3Si: 29Si-NMR Knight Shift Study

We report the measurements of the 29 Si Knight shift 29 K on the noncentrosymmetric heavy-fermion compound CePt 3 Si in which antiferromagnetism (AFM) with T N =2.2 K coexists with superconductivity (SC) with T c =0.75 K. Its spin part 29 K s , which is deduced to be K s c ≥0.11 and 0.16% at respective magnetic fields H =2.0061 and 0.8671 T, does not decrease across the superconducting transition temperature T c for the field along the c -axis. The temperature dependence of nuclear spin–lattice relaxation of 195 Pt below T c has been accounted for by a Cooper pairing model with a two-component order parameter composed of spin-singlet and spin-triplet pairing components. From this result, it is shown that the Knight-shift data are consistent with the occurrence of the two-component order parameter for CePt 3 Si.We report the measurements of the

Magnetic Properties of Single Crystalline RCu2Si2 (R: Rare Earth)

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Split Fermi Surface Properties of LaTGe3 (T: Transition Metal) and PrCoGe3 with the Non-centrosymmetric Crystal Structure

Si Knight shift

Symmetry Lowering in LaOBiS2: A Mother Material for BiS2-Based Layered Superconductors

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Calorimetric Study in Single Crystalline RCu2Si2 (R: Rare Earth)

on the noncentrosymmetric heavy-fermion compound CePt

27Al NMR Evidence for the Strong-Coupling d-Wave Superconductivity in NpPd5Al2

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