We propose a modified RKKY-technique to evaluate the magnetic properties of the ferromagnetic Kondo-lattice model. Together with a previously developed selfenergy approach to the conduction electron part of the model we get a closed system of equations which can be solved self-consistently. Ferromagnetism appears for relatively low electron (hole) densities, while it is excluded around half-filling ($n=1$). For small $J$ conventional RKKY ($\sim J^2$) is reproduced; however, with strong deviations already for very moderate exchange couplings. For not too small $n$ a critical $J_c$ is needed to produce ferromagnetism with a finite Curie temperature $T_{\textrm{C}}$, which increases with $J$, then running into a kind of saturation, in order to fall off again and disappearing above an upper critical exchange $J$.Comment: 11 pages, 14 figures, Phys. Rev. B 65, 1444XX (2002

Thermal expansion of Li0.9Mo6O17 is a-axis dominated which reduces the separation of the conducting chains at low temperature enhancing the interchain coupling. This destabilizes the Luttinger-liquid fixed point leading to an electronic charge- (or spin-) density wave dominated by Coulomb repulsion, as predicted by theories for Luttinger liquids.

A method to investigate the electron scattering characteristics of ultrathin metallic films by in situ electrical resistance measurements Rev. Sci. Instrum. 80, 073909 (2009);A procedure for determining the electrical resistivity of anisotropic materials is presented. It offers several improvements to the well-known Montgomery method. One improvement, in particular, is the ability to obtain the electrical resistivity for all three axes of an orthorhombic crystal analytically, rather than using the iterative approach suggested by Montgomery for the third axis. All necessary equations are derived and their application in determining the tensor components of the electrical resistivity is explained in detail. Measurements on isotropic specimens were executed in order to test the foundations of the method. Measurements on anisotropic samples are compared with measurements obtained by using the standard four-probe method, revealing good agreement.

The crystallographic structure of quasi-one-dimensional lithium purple bronze (LPB) was investigated using neutron powder diffraction (NPD) at temperatures T in the range 5 K < T < 295 K. It has a monoclinic symmetry with space group P 21/m, lattice parameters at 295 K are a = 12.7530(4)Å, b = 5.5239(1)Å, c = 9.4909(2)Å, and β = 90.588 (2) • . The sample stoichiometry was determined through chemical analysis and refinement of the NPD data to be Li0.924Mo6O17 The linear thermal expansion of the lattice parameters agrees with previously reported high-resolution dilatometry measurements. The bond-valence-sum method was applied to calculate the valence of each Mo ion as a function of T, which allows discussion of the mechanism by which charge is transferred between the double one-dimensional (1D) conducting chains.

SrTiO3 undergoes a cubic-to-tetragonal phase transition at 105K. This antiferrodistortive transition is believed to be in competition with incipient ferroelectricity. Substituting strontium by isovalent calcium induces a ferroelectric order. Introducing mobile electrons to the system by chemical non-isovalent doping, on the other hand, leads to the emergence of a dilute metal with a superconducting ground state. The link between superconductivity and the other two instabilities is a question gathering momentum in the context of a popular paradigm linking unconventional superconductors and quantum critical points. We present a set of specific-heat, neutronscattering,dielectric permittivity and polarization measurements on Sr1−xCaxTiO3 (0 < x < 0.009) and a study of low-temperature electric conductivity in Sr0.9978Ca0.0022TiO 3−δ . Calcium substitution was found to enhance the transition temperature for both anti-ferrodistortive and ferroelectric transitions. Moreover, we find that Sr0.9978Ca0.0022TiO 3−δ has a superconducting ground state. The critical temperature in this rare case of a superconductor with a ferroelectric parent, is slightly lower than in SrTiO 3−δ of comparable carrier concentration. A three-dimensional phase diagram for Sr1−xCaxTiO 3−δ tracking the three transition temperatures as a function of x and δ results from this study, in which ferroelectric and superconducting ground states are not immediate neighbours.

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Temperature-dependent electrical resistance in quasi-one-dimensional Li 0.9 Mo 6 O 17 is described by two Luttinger liquid anomalous exponents ␣, each associated with a distinct one dimensional band. The band with ␣ Ͻ 1 is argued to crossover to a higher dimension below the temperature T M Ј , leading to superconductivity. Disorder and magnetic fields are shown to induce the Bose metal behavior in this bulk compound.