49 research outputs found
Data user's note: Apollo 15 lunar photography
Brief descriptions are given of the Apollo 15 mission objectives, photographic equipment, and photographic coverage and quality. The lunar photographic tasks were: (1) ultraviolet photography of the earth and moon; (2) photography of the gegenschein from lunar orbit; (3) service module orbital photographic tasks; and (4) command module photographic tasks
Observation of Modulated Quadrupolar Structures in PrPb3
Neutron diffraction measurements have been performed on the cubic compound
PrPb3 in a [001] magnetic field to examine the quadrupolar ordering.
Antiferromagnetic components with q=(1/2+-d 1/2 0), (1/2 1/2+-d 0) (d~1/8) are
observed below the transition temperature TQ (0.4 K at H=0) whose amplitudes
vary linear with H and vanish at zero field, providing the first evidence for a
modulated quadrupolar phase. For H<1 T, a non-square modulated state persists
even below 100 mK suggesting quadrupole moments associated with a Gamma3
doublet ground state to be partially quenched by hybridization with conduction
electrons.Comment: Physical Review Letters, in press. 4 pages, 4 figure
Antiferro-quadrupole state of orbital-degenerate Kondo lattice model with f^2 configuration
To clarify a key role of orbitals in the emergence of
antiferro-quadrupole structure in PrPb, we investigate the ground-state
property of an orbital-degenerate Kondo lattice model by numerical
diagonalization techniques. In PrPb, Pr has a
configuration and the crystalline-electric-field ground state is a non-Kramers
doublet . In a - coupling scheme, the state is
described by two local singlets, each of which consists of two electrons
with one in and another in orbitals. Since in a cubic
structure, has localized nature, while orbitals are
rather itinerant, we propose the orbital-degenerate Kondo lattice model for an
effective Hamiltonian of PrPb. We show that an antiferro-orbital state is
favored by the so-called double-exchange mechanism which is characteristic of
multi-orbital systems.Comment: 3 pages, 3 figures, Proceedings of Skutterudite2007 (September 26-30,
2007, Kobe
Quadrupolar Kondo Effect in Non-Kramers Doublet System PrInAg2
We performed ultrasonic measurement on the rare-earth intermetallic compound
PrInAg_2 to examine the quadrupolar Kondo effect associated with the
non-Kramers Gamma_3 doublet ground state. The characteristic softening of the
elastic constant (c_{11}-c_{12})/2 below 10 K in PrInAg_2 is attributed to a
Curie term in quadrupolar susceptibility for the quadrupole O_2^2=J_x^2-J_y^2
of the stable Gamma_3 ground state. (c_{11}-c_{12})/2 turns to a slight
increase with the -lnT dependence below 0.1 K, which suggests the quenching of
the quadrupolar moment in the quadrupolar Kondo state. Under applied magnetic
fields of 10 T and 15 T above 8.7 T corresponding to the Kondo temperature T_K
of ~ 0.86 K, the behavior of (c_{11}-c_{12})/2 is described in terms of
quadrupolar susceptibility for the stable 4f^2 state.Comment: PDF, 10pages + 5figures, Strongly Correlated Electron
Quadrupolar effect and rattling motion in heavy fermion superconductor PrOs_4Sb_{12}
The elastic properties of a filled skutterudite PrOs_4Sb_{12} with a heavy
Fermion superconductivity at T_C=1.85 K have been investigated. The elastic
softening of (C_{11}-C_{12})/2 and C_{44} with lowering temperature down to T_C
indicates that the quadrupolar fluctuation due to the CEF state plays a role
for the Cooper paring in superconducting phase of PrOs_4Sb_{12}. A Debye-type
dispersion in the elastic constants around 30 K revealed a thermally activated
Gamma_{23} rattling due to the off-center Pr-atom motion obeying
tau=tau_{0}exp(E/k_{B}T) with an attempt time tau_0=8.8*10^{-11} sec and an
activation energy E=168 K. It is remarkable that the charge fluctuation of the
off-center motion with Gamma_{23} symmetry may mix with the quadrupolar
fluctuation and enhance the elastic softening of (C_{11}-C_{12})/2 just above
T_C.Comment: 5 pages, 4 figures, to be published to Phys. Rev.