  Ytterbium (Yb) metal is divalent and nonmagnetic but would be expected under
sufficient pressure to become trivalent and magnetic. We have carried out
electrical resistivity and ac magnetic susceptibility measurements on Yb to
pressures as high as 179 GPa over the temperature range 1.4 - 295 K. No
evidence for magnetic order is observed. However, above 86 GPa Yb is found to
become superconducting near 1.4 K with a transition temperature that increases
monotonically with pressure to approximately 4.6 K at 179 GPa. Yb thus becomes
the 54th known elemental superconductor.
