No abstract

We report the discovery of bulk superconductivity in the ternary intermetallics YNiSi 3 and LuNiSi 3. High-quality single crystals were grown via the Sn-flux method and studied using magnetization, specific-heat, and resistivity measurements at low temperatures. The critical temperatures obtained from these different techniques are in very good agreement and yield T c = 1.36(3) K and T c = 1.61(2) K for YNiSi 3 and LuNiSi 3 , respectively. Magnetization measurements indicate that both compounds are among the rare cases where type-I superconductivity occurs in a ternary intermetallic, however, the jump in the specific heat at the transition is lower than the value expected from BCS theory (C el /γ n T c = 1.43) in both materials and is equal to 1.14(9) and 0.71(5) for the Y and Lu compounds, respectively. Resistivity measurements exhibit sharp transitions but with critical fields μ 0 H c (0) (≈0.05 T for YNiSi 3 and ≈0.08 T for LuNiSi 3) considerably higher than those obtained from the magnetization and specific heat (≈0.01 T). First-principles density functional theory calculated electronic structure shows that these compounds have highly anisotropic and complex Fermi surfaces with one electronic and two holelike branches. One hole branch and the electron branch have a large cylindrical topology connecting the first Brillouin-zone boundaries, the former being built up by the hybridization of Y(Lu) d, Ni d, and Si p states, and the latter being built up by Ni d and Si p states. The calculated phononic structures indicate that the coupling of the Y(Lu), Ni d, and Si p electrons in the low-lying optical phonon branches is responsible for the formation of Cooper pairs and the observed superconducting state. Therefore, these compounds can be classified as anisotropic three-dimensional metals with multiband superconducting ground states in the weak-coupling regime.

No abstract

The Anderson localization of light in one-dimensional disordered photonic superlattices is theoretically studied. The system is considered to be made of alternating dispersive and nondispersive layers of different randomthickness. Dispersive slabs of the heterostructure are characterized by Drude-like frequency-dependent electric permittivities and magnetic permeabilities. Numerical results for the localization length are obtained via an analytical model, only valid in the case of weak disorder, and also through its general definition involving the transmissivity of the multilayered system. Anomalous λ 4 -and λ −4 -dependencies of the localization length in positive-negative disordered photonic superlattices are obtained, in certain cases, in the long and short wavelength limits, respectively. 141|Anomalous Localization of Light in One-Dimensional Disordered Photonic Superlattices Localización anómala de la luz en superredes fotó-nicas unidimensionales desordenadas Resumen La localización de Anderson de la luz en superredes fotónicas desordenadas unidimensionales es estudiada teóricamente. El sistema se considera compuesto de capas alternadas dispersivas y no dispersivas de diferentes espesores aleatorios. Las capas dispersivas de la heteroestructura están caracterizadas por permitividades eléctricas y permeabilidades magnéticas tipo Drude dependientes de la frecuencia. Los resultados numéricos para la longitud de la localización son obtenidos mediante un modelo analítico, solo válido en caso de desorden débil, y también a través de la definición general que involucra la transmisividad del sistema multicapas. Las dependencias anómalas λ 4 y λ −4 de la longitud de localización en superredes fotónicas desordenadas son obtenidas, en ciertos casos, en los límites de longitudes de onda larga y corta, respectivamente.Palabras clave: localización de anderson; anomalías de brewster; superredes fotónicas.