Yoshichika Onuki

Magnetic and electrical properties of U-Ge intermetallic compounds

We have clarified the magnetic and electrical properties of U 7 Ge, U 5 Ge 3 , U 3 Ge 4 and UGe 2 , measuring the electrical resistivity, thermoelectric power, Hall coefficient, magnetic susceptibility, magnetization and specific heat. U 7 Ge and U 5 Ge 3 , which are Pauli paramagnetic compounds, become superconductive below 1.40 K and 0.99 K, respectively. The latter compounds U 3 Ge 4 and UGe 2 indicate ferromagnetism. Anisotropic properties of UGe 2 are well reflected in the electrical resistivity, magnetic susceptibility and magnetization.

High-field state of the flux-line lattice in the unconventional superconductor CeCoIn5

Ultrasound velocity measurements of the unconventional superconductor CeCoIn_5 with extremely large Pauli paramagnetic susceptibility reveal an unusual structural transformation of the flux line lattice (FLL) in the vicinity of the upper critical field. The transition field coincides with that at which heat capacity measurements reveal a second order phase transition. The lowering of the sound velocity at the transition is consistent with the collapse of the FLL tilt modulus and a crossover to quasi two-dimensional FLL pinning. These results provide a strong evidence that the high field state is the Fulde-Ferrel-Larkin-Ovchinikov phase, in which the order parameter is spatially modulated and has planar nodes aligned perpendicular to the vortices.

Normal-state Hall Angle and Magnetoresistance in Quasi-2D Heavy Fermion CeCoIn5 near a Quantum Critical Point

The normal-state Hall effect and magnetoresisitance (MR) have been measured in the quasi two dimensional (2D) heavy fermion superconductor CeCoIn 5 . In the non-Fermi liquid region where the reistivity ρ x x exhibits an almost perfect T -linear dependence, the Hall angle varies as cot θ H ∝ T 2 and MR displays a strong violation of Kohlers rule. We demonstrate a novel relation between the MR and the Hall conductivity, Δρ x x /ρ x x ∝(σ x y ρ x x ) 2 . These results bear a striking resemblance to the normal-state properties of high- T c cuprates, indicating universal transport properties in the presence of quasi-2D antiferromagnetic fluctuations near a quantum critical point.The normal-state Hall effect and magnetoresisitance (MR) have been measured in the quasi-2D heavy fermion superconductor CeCoIn_5. In the non-Fermi liquid region where the reistivity rho_xx exhibits an almost perfect T-linear dependence, the Hall angle varies as cot theta_H propto T^2 and the MR displays a strong violation of Kohlers rule. We demonstrate a novel relation between the MR and the Hall conductivity, Delta rho_xx/rho_xx propto (sigma_xy rho_xx)^2. These results bear a striking resemblance to the normal-state properties of high-T_c cuprates, indicating universal transport properties in the presence of quasi-2D antiferromagnetic fluctuations near a quantum critical point.

Comment on the de Haas-van Alphen Effect in the Superconducting Mixed State of 2H–NbSe 2

We present the de Haas-van Alphen (dHvA) effect in the superconducting mixed state of 2H–NbSe 2 . Our data are consistent with the dHvA results obtained by Graebner and Robbins, which have been the subject of controversy from the viewpoint of experiment and theory. We discuss the reason why the theoretically expected cylindrical Fermi surfaces are not detected in the dHvA experiment and also the mechanism of the dHvA effect in the mixed state.

Anomalous Hall Coefficient in the f Electron system– Ce Compounds

We report the temperature dependence of Hall coefficient of RCu 6 (R: La, Ce, Pr, Nd and Sm), Ce x La 1- x Cu 6 and typical Ce compounds (CeRu 2 , CeSn 3 , CePd 3 , CeCu 2 Si 2 , CeAl 3 , CeInCu 2 , CeAl 2 , CeIn 3 and CeB 6 ) in the temperature range of 0.7 K to room temperature. The f electrons of these substances show a wide variety of behavior including Pauli itinerance, mixed valence, heavy fermion and localized moment system. These characteristics are well reflected in the Hall coefficient. The Hall coefficient of Ce x La 1- x Cu 6 at higher temperatures than 30 K is well fitted by the recent skew scattering Hall effect theory.

High Field Magnetoresistance and de Haas-van Alphen Effect in CeNi

We have measured the magnetoresistance and de Haas-van Alphen (dHvA) effect in CeNi in the field up to 150 kOe and at temperature down to 0.4 K. This material is found to be a compensated metal with equal carrier concentration of electrons and holes. The open orbits exist along the b - and c -axes. Four dHvA branches have been found in the field along the b -axis. The dHvA frequencies and the cyclotron masses are 3.60 ×10 7 Oe (10.3 m 0 ), 1.25 ×10 7 Oe (8.91 m 0 ), 6.58 ×10 6 Oe (3.05 m 0 ) and 2.15 ×10 6 Oe (2.58 m 0 ).

Magnetoresistance and de Haas-van Alphen Effect in UC

We have measured the magnetoresistance and de Haas-van Alphen oscillation of UC. The Fermi surface of semimetal UC is found to consist of three hole-ellipsoids located at the X points and six electron-ellipsoids at the W points in the fcc Brillouin zone. The cyclotron mass of electron at the direction is 2.67 m 0 , which is heavy compared to that of hole, 0.84 m 0 .

Magnetoresistance and de Haas-van Alphen Effect in the Antiferromagnetic Compound NdIn 3

We have measured the magnetoresistance and de Haas-van Alphen (dHvA) effect in both the antiferromagnetic and paramagnetic states of NdIn 3 . Many dHvA branches are detected in the dHvA experiments. Among them, a nearly spherical Fermi surface in the paramagnetic state, which corresponds to a band 7-electron Fermi surface of the non-4 f reference compound LaIn 3 , is changed in the antiferromagnetic state into a multiply connected Fermi surface with necks. The cyclotron masses of NdIn 3 are in the range of 0.30 m 0 to 1.05 m 0 , which are twice as large as those of LaIn 3 .

Effect of pressure on the T2-dependent electrical resistivity of the heavy-fermion compound CeInCu2

Abstract The temperature dependence of electrical resistivity p ( T ) of the heavy-fermion compound CeInCu 2 has been measured under hydrostatic pressure up to 8 GPa. It is found that the p ( T ) curves indicate a pressure-induced valence transition, and the resistivity-maximum temperature T max increases rapidly by applying pressure. p ( T ) at low temperatures has a T 2 dependence and the temperature range showing the T 2 term is expanded by pressure. The coefficient A of the T 2 term in p ( T ) decreases rapidly with increasing pressure. Since T max and A are proportional to T K and T K −2 respectively, where T K is the Kondo temperature, the large increase in the value of T max and decrease in A indicates the large enhancement of T K at high pressures.

Cyclotron mass and scattering lifetime in heavy electron system

From de Haas-van Alphen experiments of CeIn 3 and LaIn 3 , we have confirmed that the product of the cyclotron mass and the inverse scattering lifetime is constant.