  We report high-pressure induced superconductivity in boron nanowires (BNWs)
with rhombohedral crystal structure. Obviously different from bulk rhombohedral
boron, these BNWs show a semiconductor-metal transition at much lower pressure
than bulk boron. Also, we found these BNWs become superconductors with Tc=1.5 K
at 84 GPa, at the pressure of which bulk boron is still a semiconductor, via
in-situ resistance measurements in a diamond anvil cell. With increasing
pressure, Tc of the BNWs increases. The occurrence of superconductivity in the
BNWs at a pressure as low as 84 GPa probably arises from the size effect.
