Hydrogenated amorphous silicon has been deposited by a new technique of thermal decomposition of silane from a hot tungsten or carbon foil heated to about 1600 °C. Initial measurements indicate that the resulting films have a fairly high photoresponse. Introduction of ammonia along with silane is seen to enhance the photoconductivity quite significantly.

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High engineering critical current density J E of >500 A/mm 2 at 20 T and 4.2 K can be regularly achieved in Ag-sheathed multifilamentary Bi 2 Sr 2 CaCu 2 O x (Bi-2212) round wire when the sample length is several centimeters. However, J E (20 T) in Bi-2212 wires of several meters length, as well as longer pieces wound in coils, rarely exceeds 200 A/mm 2 . Moreover, long-length wires often exhibit signs of Bi-2212 leakage after melt processing that are rarely found in short, open-end samples. We studied the length dependence of J E of state-of-the-art powder-in-tube (PIT) Bi-2212 wires and gases released by them during melt processing using mass spectroscopy, confirming that J E degradation with length is due to wire swelling produced by high internal gas pressures at elevated temperatures [1,2]. We further modeled the gas transport in Bi-2212 wires and examined the wire expansion at critical stages of the melt processing of as-drawn PIT wires and the wires that received a degassing treatment or a colddensification treatment before melt processing. These investigations showed that internal gas pressure in long-length wires drives creep of the Ag sheath during the heat treatment, causing wire to expand, lowering the density of Bi-2212 filaments, and therefore degrading the wire J E ; the creep rupture of silver sheath naturally leads to the leakage of Bi-2212 liquid. Our work shows that proper control of such creep is the key to preventing Bi-2212 leakage and achieving high J E in long-length Bi-2212 conductors and coils.

We have studied anisotropic magnetic properties of layered intermetallic superconductor CaAlSi with moderate anisotropy. Near the upper critical field there is a prominent peak effect for H͉͉c at low temperatures and it becomes weaker for H͉͉ab. The estimated correlation length L c suggests the presence of three-dimensional collective pinning around the peak effect. The critical current densities for H͉͉c and H͉͉ab have been extracted and compared. Flux pinning mechanism in CaAlSi is anisotropic. Collective core pinning is observed for H͉͉c whereas there is a signature of deviation from it for H͉͉ab. The vortex phase diagram, including the upper critical field, irreversibility field, and peak field, has been studied. The thermodynamic critical field and Ginzburg-Landau parameter have been estimated from the equilibrium magnetization. The nature of scaling of the maximum pinning force densities with the thermodynamic critical field has been discussed. The temperature dependence of London penetration depth is consistent with single fully gapped state in CaAlSi.