Yasunori Kubo

Heavy Fermion State in YbIr2Zn20

We measured the high-field magnetization and de Haas–van Alphen (dHvA) oscillations for YbIr 2 Zn 20 with a cubic crystal structure, together with the electrical resistivity and magnetic susceptibility. The magnetic susceptibility χ with an effective magnetic moment of Yb 3+ becomes temperature-independent at low temperatures, with a broad peak at T χmax =7.4 K for H ∥ . The corresponding magnetization indicates a metamagnetic transition at H m =120 kOe, consistent with a T χmax vs H m relation in the Ce- and U-based heavy fermion compounds. The large cyclotron masses of 4–27 m 0 are detected in the dHvA experiment, and are found to be reduced at magnetic fields higher than H m =120 kOe. The resistivity follows the Fermi liquid relation ρ=ρ 0 + A T 2 under magnetic field, and the \(\sqrt{A}\) value is also found to have a maximum at H m as a function of magnetic field. From the present experimental results, together with the results of 4 f -itinerant energy band calculations, the 4 f electrons are fou...

Electromigration of In Ultrathin Film on Si(111)

The electromigration of a pad of In ultrathin film with a thickness of several monolayers on a Si(111) 7×7 surface was investigated by scanning Auger electron spectroscopy. Indium atoms moved to the cathode in the ultrathin film contrary to conventional electromigration in bulk materials and in thin films and had a mobility of 8.5×10-5 cm2/(Vs) at 80°C. This is three orders of magnitude greater than the mobility of ordinary films. The morphology of the ultrathin film in the process of the movement was studied particularly carefully and proved to be associated with the growth mode of the In film on Si(111).

Metamagnetic Behavior in Heavy-Fermion Compound YbIr2Zn20

The metamagnetic behavior in the heavy-fermion compound YbIr 2 Zn 20 with a cubic structure was studied by magnetization, de Haas–van Alphen (dHvA) oscillation, magnetoresistance, specific heat, thermal expansion, and magnetostriction measurements in single-crystalline samples. A metamagnetic anomaly at H m ≃100 kOe was found to exist in all field directions in the cubic crystal structure. The cyclotron effective mass m c * , the coefficient A in the Fermi liquid relation of electrical resistivity ρ=ρ 0 + A T 2 , and the electronic specific heat coefficient C / T indicate a peak at the metamagnetic field H m . The negative thermal expansion and negative volume magnetostriction suggest that the valence of the Yb ion gradually changes from a 4 f -itinerant state to a trivalent state with increasing magnetic field, and an almost trivalent state is realized above the metamagnetic field H m . On the other hand, the topology of the Fermi surface is approximately unchanged below and above H m in the dHvA experiment.

Magnetic Compton profiles of FCC-Ni, FCC-Fe50Ni50and HCP-Co

Experimental and theoretical directional magnetic Compton profiles (MCPs) of hcp-Co, fcc-Fe 50 Ni 50 and fcc-Ni are compared with each other to elucidate the difference of the electronic structure...

Strong Field Quenching of the Quasiparticle Effective Mass in Heavy Fermion Compound YbCo2Zn20

We found a metamagnetic like anomaly at H m ≃5 kOe in a heavy fermion compound YbCo 2 Zn 20 below the characteristic temperature T χ max =0.32 K where the ac-susceptibility shows a broad peak, suggesting that an electronic state with a very low Kondo temperature is realized. Interestingly, the metamagnetic like behavior was observed as two peaks at 4.0 and 7.5 kOe at 95 mK in the magnetic field dependence of the electronic specific heat C / T . The extremely large values of the electronic specific heat coefficient γ≃8000 mJ/(K 2 ·mol) and A =160 µΩ·cm/K 2 in the electrical resistivity ρ=ρ 0 + A T 2 at H =0 kOe are most likely due to the very low Kondo temperature. The \(\sqrt{A}\) value was, however, found to be strongly reduced from \(\sqrt{A}=12.6\) (µΩ·cm/K 2 ) 1/2 at 0 kOe to 0.145 (µΩ·cm/K 2 ) 1/2 at 150 kOe. Therefore, we considered that the corresponding cyclotron effective mass m c * , which was determined from the temperature dependence of the de Haas–van Alphen (dHvA) amplitude, is also reduced ...

Electronic Structures of the Ferromagnetic Heusler Alloys

In order to see the characteristic properties of the ferromagnetic Heusler alloys,the electronic structures of Ni 2 MnSn and Pd 2 MnSn have been calculated. The common properties of these alloys have been discussed by the present results and those obtained for Cu 2 MnAl. The spin polarizations of the constituent atoms are in good are in good agreement with experimental ones. The sigmas of the spin polarizations of the s -type conduction electrons in the inscribed spheres are consistent with the signs of the measured internal magnetic fields due to the conduction electrons.

Compton Profiles of Li in the GW Approximation

The Compton profile of Li is computed by using the occupation number obtained from a first-principles calculation of the spectral function within the GW approximation (GWA). The eigenstates and eigenenergies generated by the full-potential linearized augmented-plane-wave method in the local-density approximation are utilized in the GWA calculation. The dielectric matrix needed to form the screened potential W is computed within the random-phase approximation. The computed Compton profiles are in very good agreement with recent experimental results measured with a momentum resolution of 0.12 atomic units.

Compton Profiles due to the Band Electrons in Metallic Vanadium and Chromium

The Compton profiles due to the band electrons in vanadium and chromium are calculated from the wave functions obtained by APM method. The results are compared with other theoretical works and available experiments. The observed structures on the Compton profiles are well interpreted from the band theoretical point of view.

Spin-dependent momentum distribution in iron

Abstract Spin-dependent Compton profiles and positron annihilation angular distributions were calculated by the APW method for ferromagnetic iron and compared with the corresponding experiments. Good agreement obtained between theory and experiment on positron annihilation may support the calculated band structure over the complete extent of the occupied bands, especially the results obtained by the present theory for the s-d hybridization occurring in the d-bands.

Effects of electron correlations on Compton profiles of Li and Na in the GW approximation

The occupation number densities N ( k ) s of Li and Na are obtained from a first-principle calculation of the spectral function within the GW approximation. The dielectric matrix needed to form the screened potential W is computed within the random-phase approximation. The Compton profiles (CPs) of Li and Na are computed using the N ( k ) s. The computed CPs are in very close agreement with the results of recent high-resolution CP experiments. The renormalization factors on the Fermi surface Z F s are estimated for Li along the three principal symmetry directions. Although the Z F s are significantly smaller compared to those obtained so far using jellium models, they compare well with those evaluated from recent experimental CPs.