Point-contact study of the heavy-fermion superconductor CeCoIn5

We have investigated the differential conductance spectra of the point contacts between the heavy-fermion superconductor CeCoIn₅ and Pt. Many of them show a double-maximum structure that indicates the superconducting energy gap Δ. The Δ values derived using Blonder-Tinkham-Klapwijk model, however, varies from 0.47 to 0.77 meV, and yet they are within the scatter of the reported values. The evolution of Δ below T_c is slow as compared with that of BCS gap probably reflecting the unconventional superconductivity in CeCoIn₅.     

Magnetic properties of PrCu2 at high pressure

We report a study of the low-temperature high-pressure phase diagram of the intermetallic compound PrCu₂, by means of molecular-field calculations and ^63,65Cu nuclear-quadrupole-resonance (NQR) measurements under pressure. The pressure-induced magnetically-ordered phase can be accounted for by considering the influence of the crystal electric field on the 4f electron orbitals of the Pr³⁺ ions and by introducing a pressure-dependent exchange interaction between the corresponding local magnetic moments. Our experimental data suggest that the order in the induced antiferromagnetic phase is incommensurate. The role of magnetic fluctuations both at high and low pressures is also discussed.     

Synthesis,crystal structure and magnetic properties of Yb8Ag18.5Al47.5, Yb2Pd2Cd and Yb1.35Pd2Cd0.65

We report the synthesis of three new Yb-based compounds, Yb₈Ag_18.5Al_47.5 (Yb₈Cu₁₇Al₄₉-type, tetragonal tI74–I4/mmm), Yb₂Pd₂Cd (Mo₂B₂Fe-type, tetragonal tP10-P4/mbm) and Yb_1.35Pd₂Cd_0.65 (MnCu₂Al-type, cubic cF16–Fm3¯m). The crystal symmetry of these compounds has been determined and the complete structural characterisation carried out by single crystal and powder diffraction techniques. Two symmetry in-equivalent sites are available for the Yb ions in Yb₈Ag_18.5Al_47.5 and Yb_1.35Pd₂Cd_0.65. The 4f levels of the Yb ions are appreciably hybridised in Yb₈Ag_18.5Al_47.5 and to a lesser extent in Yb₂Pd₂Cd as inferred from the magnetisation and heat capacity data. Signatures of heavy fermion behaviour are observed in the heat capacity data of Yb₂Pd₂Cd in which the heat capacity, C/T, increases at low temperatures attaining a value of ≈600 mJ/mol K² at 1.8 K. The electrical resistivity of Yb₂Pd₂Cd follows a linear variation with temperature, T, between 1.4 and 5 K, thus indicating a possible non-Fermi liquid behaviour. In contrast, Yb ions are trivalent in Yb_1.35Pd₂Cd_0.65 and order magnetically near 1.4 K.     

Enhancing the superconducting transition temperature of the heavy fermion compound CeIrIn5 in the absence of spin correlations

We report on a pressure- (P-)induced evolution of superconductivity and spin correlations in CeIrIn(5) via the (115)In nuclear-spin-lattice-relaxation rate measurements. We find that applying pressure suppresses dramatically the antiferromagnetic fluctuations that are strong at ambient pressure. At P = 2.1 GPa, T(c) increases to T(c) = 0.8 K, which is twice T(c) (P = 0 GPa), in the background of Fermi-liquid state. This is in sharp contrast to the previous case in which a negative, chemical pressure (replacing Ir with Rh) enhances magnetic interaction and increases T(c). Our results suggest that multiple mechanisms work to produce superconductivity in the same compound CeIrIn(5).     

Non-stoichiometry and lithium intercalation in ZrSe2

The layer compound ZrSe₂ can be grown as a degenerate semiconductor, which is ascribed to the charge transfer effect of the self-intercalated Zr atoms. The self-intercalation is much concerned with the magnitude of the energy gap in the mother crystal. We have ascertained this by the transport measurement of ZrSe_2-xS_x and Ti_xZr_1-xSe₂. Intercalation of lithium in ZrSe₂ converts the mother crystal into a metallic one. Li_xZrSe₂ (x>0.4) is found to be superconductive below ca. 1.5K.     

Dynamics of coupled vortices in a pair of ferromagnetic disks

We here experimentally demonstrate that gyration modes of coupled vortices can be resonantly excited primarily by the ac current in a pair of ferromagnetic disks with variable separation. The sole gyration mode clearly splits into higher and lower frequency modes via dipolar interaction, where the main mode splitting is due to a chirality sensitive phase difference in gyrations of the coupled vortices, whereas the magnitude of the splitting is determined by their polarity configuration. These experimental results show that the coupled pair of vortices behaves similar to a diatomic molecule with bonding and antibonding states, implying a possibility for designing the magnonic band structure in a chain or an array of magnetic vortex oscillators.     

Sequential one-pot glycosylation with glycosyl N-trichloroacetylcarbamate and trichloroacetate including dehydrative approach using 1-hydroxy sugars

An efficient sequential one-pot glycosylation has been developed with glycosyl trichlorocarbamate and trichloroacetate activated by the same Lewis acid and enabled by a change in reaction temperature. The αα-selective glycosylation was achieved using glucose, galactose, and mannose substrates after investigation into the reactivities of the two types of glycosyl donors. Sequential one-pot dehydrative glycosylation, including in situ preparation of glycosyl donors followed by generation of two glycosyl bonds, provided three types of trisaccharide.     

Ukulactones A and B, new NADH-fumarate reductase inhibitors produced by Penicillium sp. FKI-3389

Screening for NADH-fumarate reductase inhibitors led to the isolation of the new polyketide compounds, ukulactones A and B (1 and 2, Fig. 1) from a culture broth of Penicillium sp. FKI-3389. The structure of ukulactone A was elucidated as a methylated derivative of prugosene A1, which was produced by Penicillium rugulosum and NOESY experiment revealed ukulactone B was a stereoisomer of ukulactone A. Ukulactone A showed potent inhibitory activity against NADH-fumarate reductase of the roundworm Ascaris suum in vitro.     

Spontaneous magnetization on the superconducting transition in UPt3

Theories predict that spontaneous magnetization occurs in the superconducting B phase in UPt₃ because of broken time-reversal symmetry. The strength of the spontaneous magnetization depends on whether it comes from spin degeneracy or orbital degeneracy. We measured the internal field due to the spontaneous magnetization on the supercondicting transition to the B phase for a UPt₃ sample in the magnetic fields very close to zero, using a SQUID magnetometer. The upper limit of the spontaneous internal field was 0.007 gauss. This result seems to favor the theory of the orbital degeneracy.