We study the superconducting properties of the noncentrosymmetric compound LaNiC 2 by measuring the London penetration depth (T ), the specific heat C(T, B) and the electrical resistivity ρ(T, B). Both λ(T ) and the electronic specific heat C e (T ) exhibit behavior at low temperatures that can be described in terms of a phenomenological two-gap Bardeen-Cooper-Schrieffer (BCS) model. The residual Sommerfeld coefficient in the superconducting state, γ 0 (B), shows a rapid increase at low fields and then an eventual saturation with increasing magnetic field. A pronounced upturn curvature is observed in the upper critical field B c2 (T ) near T c . All these experimental observations support the existence of two-gap superconductivity in LaNiC 2 .

A new optical sensing platform based on a combination of planar waveguiding and sol-gel processing technologies is described. The sensing element consists of two, submicrometer thick glass layers supported on an optically thick glass substrate; both layers were fabricated using a sol-gel coating method. The lower layer is a densified glass that functions as a planar integrated optical waveguide (IOW). The upper layer is an undensified glass of lower index doped with an optical indicator that is immobilized, yet remains sterically accessible to analytes that diffuse into the pore network. Formation of a complex between the analyte and indicator is detected via attenuated total reflection (ATR) of light guided in the IOW. Feasibility was evaluated by constructing IOW-ATR sensors for Pb2+ and pH, based on immobilized xylenol orange and bromocresol purple, respectively. The response of both sensors was sensitive and rapid, features that are difficult to achieve simultaneously in monolithic sol-gel glass sensors. In the IOW-ATR geometry, these

We report measurements of the London penetration depth ∆λ(T ) and the electronic specific heat Ce(T ) on high-quality single crystals of the filled-skutterudite superconductor PrPt4Ge12 (Tc ≃8K). Both quantities show a weak temperature dependence at T ≪ Tc, following ∆λ ∼ T n (n ≃ 3.2) and Ce/T ∼ T 2.8 . Such temperature dependences deviate from both conventional s-wave type and nodal superconductivity. A detailed analysis indicates that the superfluid density ρs(T ), derived from the penetration depth, as well as the electronic specific heat can be consistently described in terms of a two-gap model, providing strong evidence of multiband superconductivity for PrPt4Ge12. Recently, a series of new skutterudite superconductors with a germanium-platinum framework, i.e., M Pt 4 Ge 12 (M =Sr, Ba, La, Pr), were successfully synthesized [10,11]. Among all the Pr-filled variants, PrPt 4 Ge 12 shows an unexpectedly high transition temperature of T c =7. [19]. However, these experiments were performed on polycrystalline samples at relatively high temperatures, which could not make a clear assertion on the gap symmetry. The reasons underlying such discrepancies of the gap structure in PrPt 4 Ge 12 are not yet clear, and further measurements, in particular those based on high-quality single crystals, are badly needed.In this Letter, we probe the superconducting gap symmetry of PrPt 4 Ge 12 by measuring the London penetration depth ∆λ(T ) and the specific heat C p (T ) of highquality single crystals. Precise measurements of the penetration depth changes at low temperatures show ∆λ ∼ T n with n ≃ 3.2, indicating that PrPt 4 Ge 12 is actually neither a simple BCS nor a nodal superconductor. A detailed analysis of the superfluid density ρ s (T ), converted from λ(T ), and the electronic specific heat C e (T ) provide strong evidence of two-band SC for PrPt 4 Ge 12 .High-quality single crystals of PrPt 4 Ge 12 were synthesized by using multi-step thermal treatments [20]. Powder X-ray diffraction indicates the presence of a small amount of foreign phases. Energy-dispersive Xray (EDX) analysis confirms that all the crystals have a stoichiometric composition and the impurity phases, mainly PtGe 2 and free Ge, are located at the crystal surfaces [20]. In our measurements, the crystals were mechanically polished to get rid of these surface contaminations. Precise measurements of the resonant frequency shift ∆f (T ) were performed by utilizing a tunnel diode oscillator (TDO) based, self-inductance method at an operating frequency of 7 MHz down to about 0.5K

Applications of planar integrated optical waveguide (IOW) technology to problems in surface spectroscopy and optical chemical sensing have been partly limited by the difficulty of producing high-quality glass IOWs. The fabrication of IOWs by the sol-gel method from methyltriethoxysilane and titanium tetrabutoxide precursors is described here. The physical, chemical, and optical properties of the films during and after high-temperature annealing were studied using a variety of analytical techniques. The results show that the catalyst used to accelerate the sol-gel reaction strongly influenced the optical quality of the IOW. HCl catalysis produced waveguides with propagation losses of approximately 1 dB/cm, whereas in the case of SiCl4 catalysis, propagation losses were < 0.2 dB/cm, a value significantly less than any previously reported for sol-gel-derived IOWs. An examination of film surface structure and morphology by scanning electron microscopy and atomic force microscopy showed that the SiCl4-catalyzed IOWs were significantly smoother and more homogeneous on a submicrometer scale than the HCl-catalyzed IOWs. The use of SiCl4 is thought to retard formation of a microheterogeneous network containing Si-rich and Ti-rich domains, which is favored with HCl catalysis and contributes to the higher observed losses.

We present research on the superconducting properties of Nb x Re 1−x (x = 0.13-0.38) obtained by measuring the electrical resistivity ρ(T ), magnetic susceptibility χ (T ), specific heat C P (T ), and London penetration depth λ(T ). It is found that the superconducting transition temperature T c decreases monotonically with an increase of x. The upper critical field B c2 (T ) for various x can be nicely scaled by its corresponding T c . The electronic specific heat C e (T )/T , penetration depth λ(T ), and superfluid density ρ s (T ) demonstrate exponential behavior at low temperatures and can be well fitted by a one-gap BCS model. The residual Sommerfeld coefficient γ 0 (B) in the superconducting state follows a linear field dependence. All these properties suggest an s-wave BCS-type of superconductivity with a very large B c2 (0) for Nb x Re 1−x (0.13 x 0.38).