Yusuke Okuda

Pressure-Induced Heavy-Fermion Superconductivity in Antiferromagnet CeIrSi3 without Inversion Symmetry

We report the discovery of pressure-induced superconductivity in an antiferromagnet CeIrSi 3 , which lacks inversion symmetry in the tetragonal crystal structure. The Neel temperature T N = 5.0 K at ambient pressure decreases monotonically with increasing pressure, and becomes zero at about 2.5 GPa. Superconductivity appears in a wide pressure region from 1.8 GPa to about 3.5 GPa, with a relatively large superconduting transition temperature T sc = 1.6 K and a large upper critical field H c2 (0) = 11.1 T at 2.5 GPa, indicating heavy-fermion superconductivity.

Magnetic and Superconducting Properties of LaIrSi3and CeIrSi3with the Non-centrosymmetric Crystal Structure

Single crystals of LaIrSi 3 and CeIrSi 3 were grown by the Czochralski pulling method in a tetra-arc furnace and the magnetic and superconducting properties, together with superconductivity in CeIr 1- x Co x Si 3 , were clarified by measuring the electrical resistivity, specific heat, magnetic susceptibility, magnetization and de Haas–van Alphen (dHvA) effect. From the results of the dHvA experiment for LaIrSi 3 , the Fermi surface is found to split into two Fermi surfaces due to the spin–orbit interaction arising from the non-centrosymmetric crystal structure, which are separated by about 1000 K. Similar split Fermi surfaces are expected in the antiferromagnet CeIrSi 3 . The electronic state of CeIrSi 3 is tuned from the antiferromagnetic state to the superconducting state by applying pressure. The upper critical field H c2 (0) at a pressure of 2.65 GPa is found to be highly anisotropic: H c2 (0)=95 kOe for H ∥[110] and H c2 (0)≃300 kOe for H ∥[001], with the superconducting transition temperature T sc ≃...Single crystals of LaIrSi 3 and CeIrSi 3 were grown by the Czochralski pulling method in a tetra-arc furnace and the magnetic and superconducting properties, together with superconductivity in CeIr...

Fermi Surface Property of CeCoGe3 and LaCoGe3 without Inversion Symmetry in the Tetragonal Crystal Structure

We carried out the de Haas–van Alphen (dHvA) experiment of an antiferromagnet CeCoGe 3 and its reference compound LaCoGe 3 without inversion symmetry in the tetragonal crystal structure. The detect...

NON-CENTROSYMMETRIC HEAVY FERMION SUPERCONDUCTIVITY IN CeCoGe3

We measured the electrical resistivity under pressure for an antiferromagnet CeCoGe3 without inversion symmetry in the tetragonal crystal structure. The Neel temperature TN1 = 21 K at ambient pressure decreases monotonically with increasing pressure, and becomes zero at about 5.5 GPa. Superconductivity appears above 4.3 GPa, with a superconduting transition temperature Tsc = 0.72 K and a large upper critical field Hc2(0) = 7 T at 5.6 GPa. The large upper critical field Hc2(0)= 7 T exceeds the Pauli limitting field Hp (≃ 1.86Tsc)=1.3 T as in CePt3Si, CeRhSi3 and CeIrSi3. The large slope of Hc2 at Tsc, -dHc2/dT = 18T/K, at 5.6 GPa indicates the heavy-fermion superconductivity in CeCoGe3.

Evolution of an Unconventional Superconducting State inside the Antiferromagnetic Phase of CeNiGe3 under Pressure: A 73Ge-Nuclear-Quadrupole-Resonance Study

We report a 73 Ge nuclear-quadrupole-resonance (NQR) study on novel evolution of unconventional superconductivity in antiferromagnetic (AFM) CeNiGe3. The measurements of the 73 Ge-NQR spectrum and the nuclear spin-lattice relaxation rate (1=T1) have revealed that the unconventional superconduc- tivity evolves inside a commensurate AFM phase around the pressure (P) where Neel temperature TN exhibits its maximum at 8.5 K. The superconducting transition temperature TSC has been found to be enhanced with increasing TN, before reaching the quantum critical point at which the AFM order collapses. Above TSC, the AFM structure transits from an incommensurate spin-density-wave order to a commensurate AFM order at T � 2 K, accompanied by a longitudinal spin-density fluctuation. With regard to heavy-fermion compounds, these novel phenomena have hitherto never been reported in the P-T phase diagram.

Magnetic and electronic properties in CeTSi3 and CeTGe3 (T: Transition metal)

We investigated the magnetic properties of CeTSi3CeTSi3 (T: Ru, Os, Co, Rh, Ir, Pd and Pt) and CeTGe3CeTGe3 (T: Co, Rh and Ir) by measuring their electrical resistivity and magnetic susceptibility. CeRuSi3CeRuSi3, CeOsSi3CeOsSi3 and CeCoSi3CeCoSi3 do not order magnetically, with a large Kondo temperature of about 200K. The other compounds order antiferromagnetically, and are very similar to each other in their magnetic and electronic properties, which is related to a large crystalline electric field (CEF) splitting energy of the 4f4f electron, about 500K in CeIrSi3CeIrSi3.

Electronic States in a Semimetal Ce3Sn7

We carried out the de Haas–van Alphen (dHvA) measurement and the pressure experiment of the electrical resistivity for an antiferromagnet Ce 3 Sn 7 with the orthorhombic crystal structure. The detected dHvA branches are many in number and their dHvA frequencies are extremely small in magnitude, indicating that Ce 3 Sn 7 is a semimetal. This is consistent with the result of the energy band calculations under the assumption that the 4 f electrons of two Ce atoms in the 2( a ) site are localized and the 4 f electron of one Ce atom in the 4( i ) site is itinerant. In the pressure experiment, the Neel temperature of T N = 5.3 K is found to slightly increase with increasing pressure, becomes maximum around 1 GPa, then decreases steeply with further increasing pressure and most likely becomes zero between 3 and 4 GPa. The antiferromagnetic state is changed into the non-magnetic state under pressure.

Magnetic and fermi surface properties of an antiferromagnet Ce3Sn7

We measured the electrical resistivity, specific heat, magnetic susceptibility, high-field magnetization, thermal expansion and magnetostriction of an antiferromagnet Ce 3 Sn 7 with the orthorhombic crystal structure. The experimental data are found to be well explained on the basis of the crystalline electric field (CEF) 4 f -scheme previously proposed by Bonnet et al. in which the two Ce atoms at the 2(a) site possess a magnetic moment of 0.36 µ B /Ce and the one Ce atom at the 4(i) site possesses no magnetic moment as in a valence fluctuating compound CeSn 3 . We also constructed the antiferromagnetic phase diagram for the three principal directions. Furthermore, we carried out the de Haas–van Alphen experiment. Fermi surfaces are many in number but extremely small in volumes, indicating that Ce 3 Sn 7 is a semimetal.

Finite element analysis of deformation in early stage of multi-pass circumferential dissimilar welding of thick-walled pipes with narrow gap

Three-dimensional thermal elastic-plastic finite element analyses were conducted in order to reveal the mechanism of gap shrinkage in early stage of multi-pass narrow gap welding of thick-walled dissimilar pipes and thick plates. The gap shrinkage up to the 8th pass indicates that the shrinkage of plates becomes to be much larger than that of pipes with increasing the weld passes. In addition, through the decomposition of gap shrinkage to transverse shrinkage and angular distortion, it is found that the gap shrinkage of pipes is mainly governed by the transverse shrinkage, while the shrinkage of plates is influenced by both the transverse shrinkage and angular distortion. Moreover, the serial computational results with various groove shapes suggest that the transverse shrinkage of pipes almost linearly increases with increasing the weld pass, and its increment can be predicted by a linear approximation function obtained by the transverse shrinkage of plates regardless of the groove shape.

Magnetic and electronic properties in CeTSi3CeTSi3 and CeTGe3CeTGe3 (T: transition metal)

We investigated the magnetic properties of CeTSi3CeTSi3 (T: Ru, Os, Co, Rh, Ir, Pd and Pt) and CeTGe3CeTGe3 (T: Co, Rh and Ir) by measuring their electrical resistivity and magnetic susceptibility. CeRuSi3CeRuSi3, CeOsSi3CeOsSi3 and CeCoSi3CeCoSi3 do not order magnetically, with a large Kondo temperature of about 200K. The other compounds order antiferromagnetically, and are very similar to each other in their magnetic and electronic properties, which is related to a large crystalline electric field (CEF) splitting energy of the 4f4f electron, about 500K in CeIrSi3CeIrSi3.