X-Ray Diffuse Scattering in N-Methylphenazinium-Tetracyanoquinodimethane (NMP-TCNQ)(Physics)

X-ray diffuse scattering measurements of NMP-TCNQ at room temperature reveal some parts of diffuse lines at heights (l±0 : 094n) a^* from the b^*-c^* plane (l and n are integers, and n varies from 0 to 5). These diffuse lines, except those of the 0th order, can be interpreted in terms of a phonon anomaly and suggest incomplete cation-anion charge transfer in NMP-TCNQ

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

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

Possible Kondo resonance in PrFe4P12 studied by bulk-sensitive photoemission

Pr 4f electronic states in Pr-based filled skutterudites PrT4X12(T=Fe and Ru; X=P and Sb) have been studied by high-resolution bulk-sensitive Pr 3d-4f resonance photoemission. A very strong spectral intensity is observed just below the Fermi level in the heavy-fermion system PrFe4P12. The increase of its intensity at lower temperatures is observed. We speculate that this is the Kondo resonance of Pr, the origin of which is attributed to the strong hybridization between the Pr 4f and the conduction electrons.Comment: 4 pages(camera ready format), 4 figures, ReVTeX

Optical Properties of MFe_4P_12 filled skutterudites

Infrared reflectance spectroscopy measurements were made on four members of the MFe_4P_12 family of filled skutterudites, with M=La, Th, Ce and U. In progressing from M=La to U the system undergoes a metal-insulator transition. It is shown that, although the filling atom induces such dramatic changes in the transport properties of the system, it has only a small effect on lattice dynamics. We discuss this property of the compounds in the context of their possible thermoelectric applications.Comment: Manuscript in ReVTeX format, 7 figures in PostScirpt forma

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 PrRu$_4$P$_{12}$ 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$\bar{3}$ to Pm$\bar{3}$ 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 $f$ electrons.Comment: 4 pages, 5 figures, Phys. Rev. B (2004) (in press

Evidence for Magnetic Ordering Associated with Metal-Insulator Transition in SmRu4P12 Studied by Muon Spin Relaxation

Muon spin relaxation measurements on the filled skutterudite compound SmRu4P12 have been carried out in zero- and longitudinal-fields. Temperature dependence of both initial asymmetry and muon-spin depolarization rate show the appearance of a magnetically ordered state below the metal-insulator transition temperature TMI. The present study indicates that the ordering below TMI is not a non-magnetic antiferro-quadrupolar ordering but a magnetic one, which supports a scenario that a magnetic octupolar ordering occurs below TMI in SmRu4P12.Comment: 5 pages, 5 figures, Phys. Rev. B 73, 052408 (2006

Metal-insulator transition in PrRu4_4P12_{12} and SmRu4_4P12_{12} investigated by optical spectroscopy

Electronic structures of the filled-skutterudite compounds PrRu$_4$P$_{12}$ and SmRu$_4$P$_{12}$, which undergo a metal-insulator transition (MIT) at $T_{\rm MI}$ = 60 K and 16 K, respectively, have been studied by means of optical spectroscopy. Their optical conductivity spectra develop an energy gap of $\sim$ 10 meV below $T_{\rm MI}$. 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 $T_{\rm MI}$ and an appearance of new peaks below $T_{\rm MI}$. These results are discussed in terms of density waves or orbital ordering previously predicted for these compounds.Comment: 4pages, 4figures, submitted to Physical Review