Shigeo Ohara

Observation of superconductivity in heavy-fermion compounds of Ce2CoIn8

We succeeded in growing a single crystal of Ce 2 CoIn 8 by the flux method. The results of specific heat and electrical resistivity measurements indicate that Ce 2 CoIn 8 is a heavy-fermion superconductor below 0.4 K with an electronic specific heat coefficient γ as large as 500 mJ/K 2 mol-Ce.

Transport, Thermal, and Magnetic Properties of YbNi3X9 (X = Al, Ga): A Newly Synthesized Yb-Based Kondo Lattice System

We have succeeded in synthesizing a new Yb-based Kondo lattice system, YbNi 3 X 9 ( X = Al, Ga). Our study reveals that YbNi 3 Al 9 shows typical features of a heavy-fermion antiferromagnet with a Neel temperature of T N = 3.4 K. All of the properties reflect a competition between the Kondo effect and the crystalline electric field (CEF) effect. The moderate heavy-fermion state leads to an enhanced Sommerfeld coefficient of 100 mJ/(mol·K 2 ), even if ordered antiferromagnetically. On the other hand, the isostructural gallide YbNi 3 Ga 9 is an intermediate-valence system with a Kondo temperature of T K = 570 K. A large hybridization scale can overcome the CEF splitting energy, and a moderately heavy Fermi-liquid ground state with high local moment degeneracy should form at low temperatures. Note that the quality of single-crystalline YbNi 3 X 9 is extremely high compared with those of other Yb-based Kondo lattice compounds. We conclude that YbNi 3 X 9 is a suitable system for investigating the electronic s...

Pressure-induced valence crossover and novel metamagnetic behavior near the antiferromagnetic quantum phase transition of YbNi_{3}Ga_{9}.

We report electrical resistivity, ac magnetic susceptibility, and x-ray absorption spectroscopy measurements of intermediate valence YbNi_{3}Ga_{9} under pressure and magnetic field. We have revealed a characteristic pressure-induced Yb valence crossover within the temperature-pressure phase diagram, and a first-order metamagnetic transition is found below P_{c}∼9  GPa where the system undergoes a pressure-induced antiferromagnetic transition. As a possible origin of the metamagnetic behavior, a critical valence fluctuation emerging near the critical point of the first-order valence transition is discussed on the basis of the temperature-field-pressure phase diagram.

Effect of pressure on transport properties of mixed-valence compound YbAl3

The pressure effects on the electrical resistivity and the Hall effect have been measured for YbAl3 and LuAl3. LuAl3 is a normal metal and has negative pressure coefficient of resistivity -5X10(-3) kbar(-1) at room temperature, which is explained by a phonon stiffening effect. In the mixed-valence compound YbAl3, the magnetic contribution to the resistivity is increased by pressure. The Gruneisen parameter of the Kondo temperature Omega (K) = -partial derivative In T-K/partial derivative In V is estimated -7 for YbAl3 from the coefficient of the quadratic temperature dependence of the resistivity at low temperatures. The decrease of T-K with pressure indicates that the density of conduction electron states at the Fermi energy and/or the exchange of 4f and conduction electrons are suppressed by pressure in YbAl3

Monochromator for circularly polarized synchrotron radiation in the energy range of 5–250 eV

A new spherical grating monochromator with translational and rotational assembly including a normal incidence mount (SGM‐TRAIN) is under construction at BL 5A of the UVSOR Facility, IMS, and its design concept is reported. The following points have been taken into account in the design: (1) Energy range of 5–250 eV, (2) use both of undulator and bending magnet radiation, (3) linear and circular polarizations, (4) spectral purity, (5) resolution, and (6) length of beamline. It should be stressed that the SGM‐TRAIN is useful for experiments where circularly polarized synchrotron radiation is used. Moreover, the SGM‐TRAIN has the advantage that the small emittance of storage ring and the large space for a long beamline are not necessary.

Construction of a Compact Spin- and Angle-Resolved Photoelectron Spectrometer

A compact photoelectron spectrometer has been constructed to analyze energy, momentum and spin of the electronic states in condensed matter. The spectrometer consists of an electron energy analyzer, lens systems and a spin detector. The spin detector is a low-energy diffuse scattering type instrument with a potential of about 100–250 eV. The detector consists of a 90° deflector, a gold target, a four-section anode and lens systems. The detector is about 0.15×0.05×0.05 m3 in size and is rotatable along a single axis in the analysis chamber under ultra-high vacuum conditions. The parameters of the optical elements have been determined through optimization of the photoelectrons from GaAs(100) and with reference to the ray tracing calculation. The performance of the spin detector has been verified by observing the spin-polarized electrons from O/Cs/GaAs(100).

De Haas-van Alphen effect in ytterbium and uranium compounds

Abstract We have measured the de Haas-van Alphen (dHvA) effects of YbSn 3 , YbZn 11 and UGa 2 in the 4 He temperature range up to 15 T. The results for YbSn 3 show that the dHvA frequencies range from 60 to 3000 T and the cyclotron masses from 0.13 m 0 to 0.44 m 0 , where m 0 is the free electron mass. For YbZn 11 the dHvA frequencies range from 200 to 11 000 T and the cyclotron masses are nearly the same as those of YbSn 3 . These results indicate that YbSn 3 is a compensated metal and Yb ions in YbSn 3 and YbZn 11 are divalent. The dHvA frequencies of UGa 2 range from 20 to 1300 T. The observed cyclotron masses range from 0.3 m 0 to 3.3 m 0 , which are larger than those of YbSn 3 and YbZn 11 by a factor of ten. Field dependence of the dHvA frequency is observed in the lowest frequency oscillations in UGa 2 . These results indicate that the 5 f electrons in UGa 2 hybridize appreciably with the conduction electrons.

De Haas–van Alphen effect and magnetoresistance in YbBi2

We have measured the de Haas-van Alphen (dHvA) effect and the magnetoresistance in orthorhombic YbBi2. The eight dHvA branches alpha, beta, gamma, delta, epsilon, xi, eta, and theta were observed in the frequency range of 40-4000 T. The cyclotron masses range from 0.07m(0) to 1.4m(0). The lowest-frequency branch x originates from a small cylindrical Fermi surface elongated the b-axis. The branch beta corresponds to a nearly spherical Fermi surface with the frequency about 1700 T. The branches gamma, delta, epsilon, and xi with the frequencies 2000-4000 T are in limited field angle region near the b-axis. The results of the magnetoresistance are explained by above Fermi surface features with the open orbit along the h-axis

Transport properties of the heavy-fermion superconductor Ce2CoIn8

We present experimental results on the magnetic susceptibility, electrical resistivity and Hall coefficient for the normal state of Ce2CoIn8 in the temperature range 2?300 K. These results confirmed the heavy-fermion behaviour of Ce2CoIn8. The resistivity shows a linear temperature dependence in the low-temperature range, which develops remarkably with increasing pressure. This suggests that Ce2CoIn8 is near the quantum critical point.

Effect of pressure on the electrical resistivity of heavy fermion antiferromagnet Ce2RhIn8

Heavy-fermion antiferromagnet Ce2RhIn8 is structurally related to the pressure-induced superconductor CeRhIn5: We have measured pressure dependence of the electrical resistivity up to 1:6 GPa in the temperature range 1.5–300 K for Ce2RhIn8: We have found that the N! temperature TN decreases by pressure at the rate of � 0:8 KGPa � 1 : This large decrease of TN is a contrast to the case of CeRhIn5 in which TN has very weak pressure dependence. r 2003 Elsevier Science B.V. All rights reserved.