• Reich, Shimon

Abstract

<p>It is known that Cs_xWO₃, 0.3 ≥ x ≥ 0.19, is a 3D superconductor. Below x = 0.19 a transition from a metal to an insulator occurs and for x = 0.10, for example, no superconductivity is observed. We find, however, that for x ≤ 0.05 superconductivity reappears. For x = 0.005 nominal concentration we observe a critical transition T_c to the superconducting state at 5.9 K. This is observed in magnetic measurements, where a pronounced Meissner effect is present. X-ray photoelectron spectroscopy and transport measurements indicate that the SC state is confined to mesoscopic islands, some 10 nm thick on the surface of the Cs_xWO₃ doped crystals. The bulk of the crystal is practically pure WO₃. Thus during the high temperature crystal growth process, there is a redistribution of the Cs dopant as it migrates to the surface of the WO₃ crystals. From these observations, we conclude that upon reduction of the Cs nominal concentration below x = 0.05, a 2D superconductor is formed, while for x ≥ 0.19, the Cs_xWO₃ bronze is a 3D superconductor.</p>

Topics

• impedance spectroscopy
• surface
• x-ray photoelectron spectroscopy
• bronze
• superconductivity
• superconductivity