212 research outputs found
Thermodynamic and electron diffraction signatures of charge and spin ordering in La1-xCaxMnO3
No full textCompeting energy scales in doped C60
No full textSuperconductivity in doped C60 compounds is the result of several interactions of similar energy scales: the electron-phonon coupling, the conduction electron band width, and the on-ball Coulomb repulsion. The relative importance of these interactions dictates the appropriateness of electron-phonon, electron-electron or Mott-Hubbard models to describe the superconducting state. Several experiments are reviewed from which it is concluded that besides electron-phonon coupling, electron correlations need to be incorporated for a description of the superconducting state.</p
Vortex Depinning in YBa2Cu3O7: Resistive Transition Identification of the Crossover from Flux-Creep to Flux-Flow Behavior
No full textAnalysis of resistive transitions of YBa2Cu3O7, crystals reveals a scaling behavior which identifies the vortex-depinning critical field Hcp, hence the crossover in behavior from flux creep to flux flow. The inferred Hcp for YBa2Cu3O7 crystals closely approximates the magnitude and temperature dependence of Hcp derived from penetration length measurements of thin films.
Electronic Properties of Metal Doped Fullerides
No full textMetal doped C60 compounds comprise a class of materials, which includes insulators, conductors and superconductors which exhibit record superconducting transition temperatures Tc for a molecularly based solid. The moderately high values of Tc originate from the interaction of the conduction electrons with high frequency intramolecular phonons, and from the high density of states at the Fermi level. The high density of states and narrow band width arise from the small orbital overlap between the C60 molecules. Hence, both electron-phonon and electron-electron interactions are expected to be important features of the electronic structure of metal doped fullerides. Whereas superconductivity is mediated by electron-phonon interactions in the A3C60 phases, we show that electron-electron interactions determine the low temperature transport properties. We compare the electronic properties of these materials with other classes of superconductors
Magnetoelectric and multiferroic properties of ternary copper chalcogenides Cu2MIIMIVS4
No full textWe investigate theoretically the ternary copper chalcogenides with the general formula Cu2MIIMIVS4. This family of compounds can crystallize in two different non-centrosymmetric structures, I¯42m or Pnm21. We show that all the reported members of Cu2MIIMIVS4 having the Pnm21 symmetry exhibit a large spontaneous polarization. This result suggests that several of these materials are likely to be multiferroics since they order magnetically at low temperature. We discuss in detail in the framework of Landau theory the members Cu2MnSnS4 and Cu2MnGeS4 which should present both a linear magnetoelectric effect and multiferroic behavior.
Ferroelectricity in the cycloidal spiral magnetic phase of MnWO4
No full textWe investigate the relationships among magnetic, dielectric, and ferroelectric properties of a frustrated spin system MnWO4, which undergoes several magnetic phase transitions including a commensurate-incommensurate and a collinear-noncollinear transition. Dielectric and pyroelectric measurements show that the transition into a spiral magnetic ordered phase produces a ferroelectric state. The direction of the electric polarization is perpendicular to the spin rotation axis and the propagation vector of the spiral. These observations agree well with recent theoretical predictions that a cycloidal spiral magnetic ordering can result in electric polarization. In a material where ferroelectricity is induced by magnetic order, we can magnetically tune the ferroelectric transitions by exploiting the difference of the net magnetization between the ferroelectric and neighboring paraelectric phases.
Electrical Transport Properties of the Ternary Compounds UTSn, UTSb and ThTSn
No full textThe resistivity of the equiatomic ternary compounds UTSn, UTSb and ThTSn is up to two orders of magnitude larger than Mooij’s criterion: ρmax = 250 μΩcm. An exponential decrease of the resistivity at high temperatures suggest a band-gap in spite of the relatively high values for the linear specific heat coefficient γ.
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