Layer-thickness dependence of the conductive properties of Mo/Si multilayers

We report new measurements of the conductance and superconducting transition temperature of a set of Mo/Si multilayers, as a function of the metal layer thickness (from 7-85 Angstrom) for a constant semiconductor layer thickness of 22 Angstrom. Unlike previously reported measurements, we do not observe oscillations in either the resistivity, resistivity ratio, or the superconducting transition temperature with the metal layer thickness. Rather, we observe monotonic variations in the transport properties as the metal layer thickness increases. The sheet conductance and its change between 10 and 300 K both vary approximately linearly with the metal layer thickness, above a threshold thickness. The conductance starts to grow with metal layer thickness at approximately 10 Angstrom, whereas the temperature coefficient of resistance changes sign at approximately 25 Angstrom, exhibiting a Mooij correlation with a crossover resistivity of 125 mu Omega cm. The observed temperature dependence of the conductance rules out localization as the origin of the negative temperature coefficient of resistance. The conductance data are analyzed using a simple phenomenological model involving transport in interfacial and metallic layers, whose relative contribution to the conductance depends on the metal layer thickness and the temperature. The model is applied to separate two competing contributions that determine the overall temperature dependence of the conductance. We attribute the differences between our measurements and previous measurements to differences in bulk metallic conductivities and interface morphologies, due to differences in thermal evaporation versus sputtering fabrication processes. Our results show that the level and nature of disorder is an important ingredient in any theory that explains the cause of the observed oscillations

At-risk elementary school children with one year of classroom music instruction are better at keeping a beat

Temporal processing underlies both music and language skills. There is increasing evidence that rhythm abilities track with reading performance and that language disorders such as dyslexia are associated with poor rhythm abilities. However, little is known about how basic time-keeping skills can be shaped by musical training, particularly during critical literacy development years. This study was carried out in collaboration with Harmony Project, a non-profit organization providing free music education to children in the gang reduction zones of Los Angeles. Our findings reveal that elementary school children with just one year of classroom music instruction perform more accurately in a basic finger-tapping task than their untrained peers, providing important evidence that fundamental time-keeping skills may be strengthened by short-term music training. This sets the stage for further examination of how music programs may be used to support the development of basic skills underlying learning and literacy, particularly in at-risk populations which may benefit the most