Ultrafast response of plasmalike reflectivity edge in(TMTTF)2AsF6driven by a 7-fs 1.5-cycle strong-light field

The strong-light field effect of ${(\mathrm{TMTTF})}₂\mathrm{As}{\mathrm{F}}₆$ was investigated utilizing 1.5-cycle, 7-fs infrared pulses. The ultrafast $(\ensuremath{\sim}20\phantom{\rule{0.16em}{0ex}}\mathrm{fs})$ and large $(\ensuremath{\sim}40%)$ response of the plasmalike reflectivity edge $(\ensuremath{\sim}0.7\phantom{\rule{0.16em}{0ex}}\mathrm{eV})$ was analyzed by the changes in ${\ensuremath{\omega}}_p=\sqrt{n{e}²/({\ensuremath{\varepsilon}}_{\ensuremath{\infty}}{\ensuremath{\varepsilon}}₀m)}$ ($n$: number of charges in the $frac14\text{\ensuremath{-}}$filled band; $m$: mass of charge; ${\ensuremath{\varepsilon}}_{\ensuremath{\infty}},{\ensuremath{\varepsilon}}₀$: dielectric constants for high frequency and vacuum; $e$: elementary charge). The 3% reduction in ${\ensuremath{\omega}}_p$ is attributed to the 6% increase in $m$. Furthermore, 20 fs oscillation of ${\ensuremath{\omega}}_p$ in the time domain indicates that the plasmalike edge is affected by the charge gap $(\ensuremath{\sim}0.2\phantom{\rule{0.16em}{0ex}}\mathrm{eV})$ nature. Theoretical calculations suggest that the Coulomb repulsion plays an important role in the increase in $m$.