344 research outputs found
Hybridization effects and multipole orders in Pr skutterudites
Theoretical account is given of 4f-electron dynamics and multipole orders in
Pr skutterudites with particular attention to (i) mechanism of the crystalline
electric field (CEF) splitting leading to a pseudo-quartet ground state;(ii)
Kondo effect due to exchange interactions involving the pseudo-quartet;(iii)
multipole orders in the lattice of the pseudo-quartet in magnetic
field.Competition between the point-charge interaction andhybridization between
4f and conduction electrons is identified as the key for controlling the CEF
splitting. It is found that one of two pseudo-spins forming the pseudo-quartet
has a ferromagnetic exchange, while the other has an antiferromagnetic exchange
with conduction electrons. The Kondo effect is clearly seen in the resistivity
calculated by the NCA, provided the low-lying triplet above the singlet is
mainly composed of the -type wave functions.If the weight of the
-type is large in the triplet, the Kondo effect does not appear.This
difference caused by the nature of the triplet explains the presence of the
Kondo effect inPrFeP, and its absence in PrOsSb.By taking
the minimal model with antiferro-quadrupole (AFQ) and ferro-type intersite
interactions for dipoles and octupoles between nearest-neighbors,the mean-field
theory reproduces the overall feature of the multiple ordered phases in
PrFeP. The AFQ order with the -type symmetry is found to
be stable only as a mixture of and components.Comment: 21 pages, to be published in proc. YKIS200
Diffraction from Ordered States of Higher Multipoles
Possible ways of identification are discussed of an electronic order of
higher multipoles such as octupoles and hexadecapoles. A particularly powerful
method is resonant X-ray scattering (RXS) using quadrupolar resonance processes
called E2.The characteristic azimuthal angle dependence of
CeLaB is interpreted as evidence of antiferro-octupole
order. For PrRuP, eightfold pattern against azimuthal angle is
predicted if its metal-insulator transition is a consequence of a hexadecapole
order. In non-resonant superlattice Bragg scattering, hexadecapole contribution
may also be identified because of absence of quadrupole component.Comment: Invited paper to be published in Proc. Hiroshima Workshop on Novel
Functional Materials with Multinary Freedoms (Physica B, 2006
Recording system for the solar neutron monitoring at Mt. Norikura
To monitor solar neutron events, a new recording system will be installed at Mt. Norikura Cosmic Ray Observatory. The recording system is composed of a pulse counter with clock and a microcomputer with minifloppy disk. The counter and the microcomputer are connected through the General Purpose Interface Bus line. The one minute total count of the neutron monitor is recorded on the minifloppy disk
On the Hidden Order in URuSi --- Antiferro Hexadecapole Order and its Consequences
An antiferro ordering of an electric hexadecapole moment is discussed as a
promising candidate for the long standing mystery of the hidden order phase in
URuSi. Based on localized -electron picture, we discuss the
rationale of the selected multipole and the consequences of the antiferro
hexadecapole order of symmetry. The mean-field solutions and
the collective excitations from them explain reasonably significant
experimental observations: the strong anisotropy in the magnetic
susceptibility, characteristic behavior of pressure versus magnetic field or
temperature phase diagrams, disappearance of inelastic neutron-scattering
intensity out of the hidden order phase, and insensitiveness of the NQR
frequency at Ru-sites upon ordering. A consistency with the strong anisotropy
in the magnetic responses excludes all the multipoles in two-dimensional
representations, such as . The expected azimuthal angle
dependences of the resonant X-ray scattering amplitude are given. The
-type antiferro quadrupole should be induced by an in-plane
magnetic field along , which is reflected in the thermal expansion and
the elastic constant of the transverse mode. The
-type [-type] antiferro quadrupole is also induced by
applying the uniaxial stress along direction [ direction]. A
detection of these induced antiferro quadrupoles under the in-plane magnetic
field or the uniaxial stress using the resonant X-ray scattering provides a
direct redundant test for the proposed order parameter.Comment: 10 pages, 10 figures, 5 table
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