Formation of a HighTcElectron-Hole Liquid in Diamond

We report on the observation of electron-hole ( $e-h$) liquid (EHL) in diamond by time-resolved luminescence measurements under an intense femtosecond photoexcitation above the band gap. The EHL luminescence band is observed below the $e-h$ plasma band, showing a finite rise time of several tens of picoseconds. The rise time, which corresponds to the nucleation and the growth of the $e-h$ droplets, plummets on approaching the EHL critical temperature. Time-resolved spectral shape analysis reveals a very high carrier density of $1\times {10}^{20}{\mathrm{cm}}^{-3\mathrm{}}$ and very high critical temperature of $T_c=165\mathrm{}\mathrm{K}$ of EHL.