R. Viennois

Seebeck effect in Fe1+xTe1-ySey single crystals

We present measurements of resistivity and thermopower S of Fe1+xTe1-ySey single crystalline samples with y=0, 0.1, 0.2, 0.3, and 0.45 in zero field and in a magnetic field B=8 T. We find that the shape of thermopower curves appears quite peculiar in respect to that measured in other Fe-based superconducting families. We propose a qualitative analysis of the temperature behavior of S, where the samples are described as almost compensated semimetals: different electron and hole bands with similar carrier concentrations compete and their relative contribution to the thermoelectric transport depends on the respective filling, mobility, and coupling with phonons. For y >= 0.2, superconductivity occurs and the optimum Se-doping level for a maximum T-c of 13 K turns out to be y=0.3. At low temperatures, evidence of a contribution to S by an excitation-drag mechanism is found while at high temperatures a strikingly flat behavior of S is explained within a narrow-band Hubbard model.

Electron spin resonance and exchange paths in the orthorhombic dimer system Sr2VO4

uckel tight-binding analysis, we identify the strongest exchange interaction to occur between two inequivalent vanadium sites via two intermediate oxygen ions. The ESR absorption spectra can be well fitted by a single Lorentzian line and the temperature dependence of the ESR intensity, and the dc susceptibility can be modeled by using the Bleaney-Bowers approach for independent dimers. The temperature dependence of the ESR linewidth at X-band frequency can be modeled by a superposition of a linear increase with temperature with a slope α = 1.35 Oe/K and a thermally activated behavior with an activation energy �/k B = 1418 K, both of which point to spin-phonon coupling as the dominant relaxation mechanism in this compound.

Optical study of phonons and electronic excitations in tetragonal Sr_{2}VO_{4}

We report on the optical excitation spectra in Sr

Inelastic neutron scattering study of Ni-substituted Ce0.5Fe4Sb12 skutterudite compounds

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Physical properties of the skutterudites (Ce,La)Fe/sub 4-x/Ni/sub x/Sb/sub 12/

VO

Neutron study of rare earth filling and physical properties in R/sub y/(Fe,Ni)/sub 4/Sb/sub 12/ (with R=La or Ce)

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Influence of an electron-phonon subsystem on specific heat and two-photon absorption of the semimagnetic semiconductors Pb1-xYbxX (X = S, Se, Te) near the semiconductor-isolator phase transformation

. The phonon modes are assigned and their evolution with temperature is discussed in the frame of the different phase transitions crossed upon cooling. Besides the expected infrared-active phonons we observe two additional excitations at about 290 cm

Kondo effect, crystalline electric fields and itinerant magnetism in antimony-based filled skutterudites

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Photoinduced second harmonic generation of LaFe4Sb12 near spin fluctuated critical points

and 840 cm

Photoinduced non-linear optical monitoring of novel semimagnetic semiconductors Pb1-xYbxX (X=S, Se, Te)

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