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.

High-resolution thermal expansion measurements of single crystalline BaFe 1.84 Co 0.16 As 2 and BaFe 1.77 Co 0.23 As 2 in the temperature range 5 Ͻ T Ͻ 300 K are reported. The thermal expansion is highly anisotropic, with the largest expansion along the c axis. Distinct anomalies are present at the normal-tosuperconducting phase-transition temperature T c ; the phase transition appears to be continuous. No structural transitions are observed over the temperature range of our measurements. The thermal expansion data and heat-capacity data acquired on the same specimens are used to estimate the volumetric pressure derivative of T c using the Ehrenfest relation.

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.

Nb2SnC is a member of the large family of lamellar materials that crystallize in the hexagonal structure with space group P63/mmc which are isomorphs with Cr2AlC, also named H-phase. In spite of the great number of compounds which belong to this family, the superconductivity has been reported only for two cases: Mo2GaC and Nb2SC. In this work we show that superconductivity can be observed in Nb2SnC depending on the synthesis method used. The quality of the superconductor is strongly dependent of the synthesis method and the optimal results were reached for samples synthesized at 2.5 GPa and 523 +/- 50oC. This sample showed a critical temperature close to 7.8K, revealed from magnetization and transport measurement, the highest critical temperature reported up to now for an H-phase.Comment: paper with 12 pages and 4 figure

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