Incoherent non-Fermi liquid scattering in a Kondo lattice

One of the most notorious non-Fermi liquid properties of both archetypal heavy-fermion systems [1-4] and the high-Tc copper oxide superconductors [5] is an electrical resistivity that evolves linearly with temperature, T. In the heavy-fermion superconductor CeCoIn5 [5], this linear behaviour was one of the first indications of the presence of a zero-temperature instability, or quantum critical point. Here, we report the observation of a unique control parameter of T-linear scattering in CeCoIn5, found through systematic chemical substitutions of both magnetic and non-magnetic rare-earth, R, ions into the Ce sub-lattice. We find that the evolution of inelastic scattering in Ce1-xRxCoIn5 is strongly dependent on the f-electron configuration of the R ion, whereas two other key properties -- Cooper-pair breaking and Kondo-lattice coherence -- are not. Thus, T-linear resistivity in CeCoIn5 is intimately related to the nature of incoherent scattering centers in the Kondo lattice, which provides insight into the anomalous scattering rate synonymous with quantum criticality [7].Comment: 4 pages, 3 figures (published version

Magnetic structures and reorientation transitions in noncentrosymmetric uniaxial antiferromagnets

A phenomenological theory of magnetic states in noncentrosymmetric tetragonal antiferromagnets is developed, which has to include homogeneous and inhomogeneous terms (Lifshitz-invariants) derived from Dzyaloshinskii-Moriya couplings. Magnetic properties of this class of antiferromagnets with low crystal symmetry are discussed in relation to its first known members, the recently detected compounds Ba2CuGe2O7 and K2V3O8. Crystallographic symmetry and magnetic ordering in these systems allow the simultaneous occurrence of chiral inhomogeneous magnetic structures and weak ferromagnetism. New types of incommensurate magnetic structures are possible, namely, chiral helices with rotation of staggered magnetization and oscillations of the total magnetization. Field-induced reorientation transitions into modulated states have been studied and corresponding phase diagrams are constructed. Structures of magnetic defects (domain-walls and vortices) are discussed. In particular, vortices, i.e. localized non-singular line defects, are stabilized by the inhomogeneous Dzyaloshinskii-Moriya interactions in uniaxial noncentrosymmetric antiferromagnets.Comment: 18 pages RevTeX4, 13 figure

IV. TRANSPORTELECTRONIC STRUCTURE OF EUB6, TRANSPORT AND MAGNETIC PROPERTIES

On montre que dans les composés non magnétiques R++B6, le défaut le plus courant, la lacune R++, peut piéger un troisième trou en créant un électron de conduction comparateur, ceci à cause du caractère de semiconducteur à bande interdite étroite. Cet electron est faiblement piégé et donc donne lieu facilement à une conduction de type n. Différentes propriétés de transport sont expliquées par ce modèle. Dans EuB6 magnétique le défaut précédent forme un amas à moment géant. De plus, à cause de l'effet d'anti-liaison avec les niveaux 4f, les tander de valence de spin parallèle sont faussées à l'intérieur des tander de conduction dans l'état ferromagnétique, créant plusieurs électrons de conduction. Différentes propriétées anormales magnétiques et de transport sont expliquées dans ce modèle.In non-magnetic R++B6, it is shown that the most common defect R++ vacancy can trap third hole creating a compensating conduction electron due to the narrow gap semiconductor character. The latter is trapped loosely and thus easily causes n-type character. Various transport properties are explained on this model. In magnetic EuB6, the above defect center makes a giant moment cluster. Furthermore, due to the antibonding effect with the 4f levels, the valence bands of the parallel spin are pushed up into the conduction bands in ferromagnetic state creating many conduction electrons. Various anomalous magnetic and magneto transport properties are explained on this model

Magnetic and thermal properties of TmV<inf>2</inf>Al<inf>20</inf> single crystals

The magnetization and specific heat of TmV2Al20 single crystals were measured in the temperature range from 0.5 to 300K in external magnetic fields up to 7 T. TmV2Al20 was found to be paramagnetic above 0.5 K. Clear magnetic anisotropy was observed along the three principal crystallographic axes in the field above 1 T at 0.5 K. The magnetically easy axis is along the [100] direction, and the hard axis is along the [111] direction. On cooling below 2K in zero external field, the magnetic part of specific heat divided by temperature, Cmag=T, increases up to 6 J=molK2 near 0.6 K. The magnetic entropy in zero field reaches R ln 5 near 10 K, suggesting that the ground state of Tm3+ ions is a nonmagnetic doublet state with the first excited state of a magnetic triplet state nearby (a pseudo-fivefold degenerate state). The experimental results were reproduced by the crystalline electric field calculations, and an energy level scheme was proposed. The enhanced value of Cmag=T in the lowest temperature region in zero field was explained by assuming an energy splitting of the doublet ground state