Possible explanation for the high superconducting Tc in bcc Ti at high pressure

By means of $a\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ calculations, the authors show here that neither a conventional nor an unconventional pairing mechanism can justify the observed 26-K superconducting ${T}_c$ in compressed bcc titanium. They reconcile experimental and theoretical results by assuming the presence of Ti vacancies. These induce a phonon softening that increases the electron-phonon coupling at high pressure, yielding an agreement with measurements over the full pressure range 150--300 GPa. The proposed mechanism applies to multiple types of defects and can occur in several simple metals.