3,025 research outputs found
Charge-Density-Wave Ordering in the Metal-Insulator Transition Compound PrRu4P12
X-ray and electron diffraction measurements on the metal-insulator (M-I)
transition compound PrRuP have revealed the emergence of a periodic
ordering of charge density around the Pr atoms. It is found that the ordering
is associated with the onset of a low temperature insulator phase. These
conclusions are supported by the facts that the space group of the crystal
structure transforms from Im to Pm below the M-I transition
temperature and also that the temperature dependence of the superlattice peaks
in the insulator phase follows the squared BCS function. The M-I transition
could be originated from the perfect nesting of the Fermi surface and/or the
instability of the electrons.Comment: 4 pages, 5 figures, Phys. Rev. B (2004) (in press
Metal-insulator transition in PrRuP and SmRuP investigated by optical spectroscopy
Electronic structures of the filled-skutterudite compounds PrRuP
and SmRuP, which undergo a metal-insulator transition (MIT) at
= 60 K and 16 K, respectively, have been studied by means of
optical spectroscopy. Their optical conductivity spectra develop an energy gap
of 10 meV below . The observed characteristics of the energy
gap are qualitatively different from those of the Kondo semiconductors. In
addition, optical phonon peaks in the spectra show anomalies upon the MIT,
including broadening and shifts at and an appearance of new peaks
below . These results are discussed in terms of density waves or
orbital ordering previously predicted for these compounds.Comment: 4pages, 4figures, submitted to Physical Review
Single Crystal Growth of Skutterudite CoP3 under High Pressure
A new method to grow single crystals of skutterudite compounds is examined.
Using a wedge-type, cubic-anvil, high-pressure apparatus, single crystals of
CoP3 were grown from stoichiometric melts under a pressure of 3.5 GPa. Powder
x-ray diffraction and electron probe microanalysis measurements indicate that
the as-grown boules are a single phase of CoP3. The results suggest that CoP3
is a congruent melting compound under high pressure.Comment: 6pages,5 figures, J. Crystal Growth (in press
Role of p-f Hybridization in the Metal-Non-Metal Transition of PrRu4P12
Electronic state evolution in the metal-non-metal transition of PrRu4P12 has
been studied by X-ray and polarized neutron diffraction experiments. It has
been revealed that, in the low-temperature non-metallic phase, two inequivalent
crystal-field (CF) schemes of Pr3+ 4f^2 electrons with Gamma_1 and Gamma_4^(2)
ground states are located at Pr1 and Pr2 sites forming the bcc unit cell
surrounded by the smaller and larger cubic Ru-ion sublattices, respectively.
This modulated electronic state can be explained by the p-f hybridization
mechanism taking two intermediate states of 4f^1 and 4f^3. The p-f
hybridization effect plays an important role for the electronic energy gain in
the metal-non-metal transition originated from the Fermi surface nesting.Comment: 5 pages, 5 figures. Accepted by J. Phys. Soc. Jp
XANES study of rare-earth valency in LRu4P12 (L = Ce and Pr)
Valency of Ce and Pr in LRu4P12 (L = Ce and Pr) was studied by L2,3-edge
x-ray absorption near-edge structure (XANES) spectroscopy. The Ce-L3 XANES
spectrum suggests that Ce is mainly trivalent, but the 4f state strongly
hybridizes with ligand orbitals. The band gap of CeRu4P12 seems to be formed by
strong hybridization of 4f electrons. Pr-L2 XANES spectra indicate that Pr
exists in trivalent state over a wide range in temperature, 20 < T < 300 K. We
find that the metal-insulator (MI) transition at TMI = 60 K in PrRu4P12 does
not originate from Pr valence fluctuation.Comment: 4 page
Theory of Metal-Insulator Transition in PrRu4P12 and PrFe4P12
All symmetry allowed couplings between the 4f^2-electron ground state doublet
of trivalent praseodymium in PrRu4P12 and PrFe4P12 and displacements of the
phosphorus, iron or ruthenium ions are considered. Two types of displacements
can change the crystal lattice from body-centred cubic to simple orthorhombic
or to simple cubic. The first type lowers the point group symmetry from
tetrahedral to orthorhombic, while the second type leaves it unchanged, with
corresponding space group reductions Im3 --> Pmmm and Im3 --> Pm3 respectively.
In former case, the lower point-group symmetry splits the degeneracy of the
4f^2 doublet into states with opposite quadrupole moment, which then leads to
anti-quadrupolar ordering, as in PrFe4P12. Either kind of displacement may
conspire with nesting of the Fermi surface to cause the metal-insulator or
partial metal-insulator transition observed in PrFe4P12 and PrRu4P12. We
investigate this scenario using band-structure calculations, and it is found
that displacements of the phosphorus ions in PrRu4P12 (with space group
reduction Im3 --> Pm3) open a gap everywhere on the Fermi surface.Comment: 6 page
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