Hiroshi Yamagami

Fermi surface properties and de Haas–van Alphen oscillation in both the normal and superconducting mixed states of URu2Si2

Abstract We have succeeded in growing a high-quality single crystal of URu2Si2 with a residual resistivity ratio of 255 and performed magnetoresistance and de Haas–van Alphen (dHvA) experiments. The dHvA oscillations were observed clearly in both the normal and superconducting mixed states. From the magnetoresistance experiments, it is concluded that URu2Si2 is a compensated metal with equal carrier numbers of electrons and holes. In the dHvA experiments we observed three kinds of Fermi surfaces. We studied precisely the Fermi surface properties in both the normal and mixed states. The dHvA frequency does not change in magnitude between the normal and mixed states, while the cyclotron effective mass is reduced, and the corresponding Dingle temperature or scattering rate of the conduction electron increases in the mixed state.

The Fermi Surface of Itinerant 4f Electrons in CeNi

Based on the itinerant-electron model for the 4f electrons, the energy band structure and the Fermi surface is calculated for the mixed-valence cerium compound CeNi and its reference material LaNi by a self-consistent relativistic APW method with the exchange and correlation potential in the local-density approximation. Both CeNi and LaNi are compensated metals, and their hole and electron Fermi surfaces are multiply-connected sheets with open orbits, the direction of which is consistent with the high-field magnetoresistance. Though they are quite different from each other, the Fermi surfaces for CeNi and LaNi can explain reasonably well both the magnitude and the angle dependence of the de Haas-van Alphen effect frequency branches. These theoretical results suggest that the 4f electrons may be itinerant in the ground state in CeNi, as they are in CeSn 3 .

Fermi surface of the heavy-fermion superconductor UPd2Al3

Abstract UPd2Al3 is a heavy fermion superconductor with T c ≊ 2 K co-existent with an antiferromagnetically ordered state (TN = 14.5 K. We report the angular dependence of the dHvA frequency, the effective cyclotron mass and the Dingle temperature. A comparison of the experimental results with band-structure calculations is made, revealing that 5f electrons in UPd2Al3 are fairly itinerant.

Fermi surface of the ferromagnetic heavy-electron compound UGe2

Abstract In the itenerant 5f electron model, the Fermi surface is derived phenomenologically for the heavy-electron ferromagnet UGe2 using a relativistic APW method. The main de Haas-van Alphen frequencies together with the cyclotron effective masses can be explained reasonably well.

Magnetic and Fermi Surface Properties of the Ferromagnetic Compound UGa2.

We have studied the magnetic and Fermi surface properties in a ferromagnet UGa 2 . The electrical resistivity, elastic constant, thermal expansion coefficient, thermoelectric power, magnetic susceptibility and Hall coefficient indicate highly anisotropic properties, reflecting the hexagonal structure. The 5 f 2 - and 5 f 3 -CEF schemes, based on the localized 5 f -electron nature, are discussed to understand the magnetic susceptibility and magnetization data. We have also done the magnetoresistance and de Haas-van Alphen (dHvA) experiments to investigate the Fermi surface properties. Both data are very complicated, implying that the Fermi surface is a multiply-connected one. They are explained neither by the localized 5 f 2 - and 5 f 3 -core models nor by the spin-polarized 5 f -itinerant model. The cyclotron mass is, however, rather light, ranging from 0.17 to 6.2 m 0 , which is consistent with the electronic specific heat coefficient of 11 mJ/K 2 ·mol.

De Haas-van Alphen Effect and Energy Band Structure in UB2

We grew a single crystal of UB 2 with the hexagonal structure and observed the de Haas-van Alphen (dHvA) oscillation. All of the dHvA branches, which are about seven in number, are detected in the limited angle regions. They are well explained by the 5 f -itinerant relativistic band theory with an exchange and correlation potential in a local density approximation. Namely, UB 2 is a compensated metal with an equal number of electron and hole. The Fermi surface consists of two closed but corrugated Fermi surfaces. The cyclotron masses are moderately heavy, ranging from 1.2 to 7.7 m 0 .

Relativistic electronic structure and Fermi surface of URu2Si2 in antiferromagnetic state

Abstract A self-consistent calculation of electronic band structure for antiferromagnetically ordered URu2Si2 is performed using an all-electron fully relativistic spin-polarized LAPW method with exchange-correlation potentials in a local density approximation. The obtained magnetic moment at the uranium site shows a tiny value of 0.09μB due to cancellation between the spin and the orbital moment. It explains the small value of 0.04μB observed by neutron-scattering measurement. The Fermi surfaces are figured out from the band structure, and origins of the frequency-branches measured by de Haas–van Alphen effect are revealed.

Electronic structure of UC studied by X-ray photoemission and bremsstrahlung isochromat spectroscopy

Abstract X-ray photoemission and bremsstrahlung isochromat spectra are measured for UC. Valence state spectra are compared with the relativistic APW band calculation. Shape analysis of the U 4f core spectrum is made by Doniach-Sunjic lineshape with broadening. The discrepancies between valence spectra and the APW calculations, and presence of U 4f satellites show a correlation effect between U 5f electrons.

Band Theory of Itinerant f-Electron Compounds

Recent progress of band theory for the Fermi surface in the Ce and the U compounds is reported. A symmetrized relativistic APW method has been completed and applied to some compounds in which the de Haas-van Alphen effect (dHvA) has recently been measured. The exchange and correlation interaction of electrons are taken into account within the framework of the local-density approximation. On the basis of the itinerant-electron model for the 4f electrons, it has been revealed that the origins of the major dHvA frequency branches observed in the valence-fluctuating compound CeSn 3 can be clarified reasonably well by band theory

De Haas-van Alphen Effect and RLAPW-Energy Band Calculations in CeNi

We have carried out the de Haas-van Alphen (dHvA) experiments in a valence fluctuating compound CeNi. Forty seven dHvA branches are observed experimentally, which are mainly centered at the symmetrical axes. Most of the dHvA branches are approximately explained by the 4 f -itinerant band model. The cyclotron mass is in the range from 3.0 to 27 m 0 . Branch α, which has the largest cross-sectional area of the Fermi surface in the detected branches along the a -axis, has the cyclotron mass of 27 m 0 . This mass is five times larger than the corresponding band mass of 5.45 m 0 .