  It is challenging to search for high Tc superconductivity (SC) in transition
metal elements wherein d electrons are usually not favored by conventional BCS
theory. Here we report discovery of surprising SC up to 310 GPa with Tc above
20 K in wide pressure range from 108 GPa to 240 GPa in titanium. The maximum
Tc^onset above 26 K and zero resistance Tc^zero of 21 K are record high values
hitherto achieved among element superconductors. The Hc2(0) is estimated to be
about 32 Tesla with coherence length 32 angstrom. The results show strong s-d
transfer and d-band dominance, indicating correlation driven contributions to
high Tc SC in dense titanium. This finding is in sharp contrast to the
theoretical predications based on pristine electron-phonon coupling scenario.
The study opens a fresh promising avenue for rational design and discovery of
high Tc superconductors among simple materials via pressure tuned
unconventional mechanism.
