Ultrafast response of plasmalike reflectivity edge in ${\left(\mathrm{TMTTF}\right)}_2\mathrm{As}{\mathrm{F}}_6$ driven by a 7-fs 1.5-cycle strong-light field

The strong-light field effect of ${\left(\mathrm{TMTTF}\right)}_2\mathrm{As}{\mathrm{F}}_6$ was investigated utilizing 1.5-cycle, 7-fs infrared pulses. The ultrafast $(\sim 20\mathrm{fs})$ and large $(\sim 40\%)$ response of the plasmalike reflectivity edge $(\sim 0.7\mathrm{eV})$ was analyzed by the changes in ${\omega }_p=\sqrt{n{e}^2/\left({\varepsilon }_{\infty }{\varepsilon }_{0}m\right)}$ ($n$: number of charges in the $frac14\text{−}$filled band; $m$: mass of charge; ${\varepsilon }_{\infty },{\varepsilon }_0$: dielectric constants for high frequency and vacuum; $e$: elementary charge). The 3% reduction in ${\omega }_p$ is attributed to the 6% increase in $m$. Furthermore, 20 fs oscillation of ${\omega }_p$ in the time domain indicates that the plasmalike edge is affected by the charge gap $(\sim 0.2\mathrm{eV})$ nature. Theoretical calculations suggest that the Coulomb repulsion plays an important role in the increase in $m$.

Figure 1

(a) Optical conductivity $\left(\sigma \right)$ spectra of ${(\mathrm{TMTTF})}_2\mathrm{As}{\mathrm{F}}_6$ at 25 and 150 K. The spectrum of the 7-fs pulse (orange shaded area) is also shown. (b) Reflectivity ($R$) spectra at 25 and 150 K with the Lorentz analysis (solid lines). Inset shows the temperature dependence of $\mathrm{\Delta }\gamma /\gamma$.

Figure 2

(a) Time evolution of the transient reflectivity $(\mathrm{\Delta }R/R)$ at $t_d<4\mathrm{ps}$ measured by a 100-fs pulse. (b) $\mathrm{\Delta }R/R$ spectrum at $t_d=0.1\mathrm{ps}$ with the Lorentz analysis (solid line). (c) Spectral change calculated with only decreasing ${\omega }_p$ (1.8%) (blue) and that with only increasing $\gamma$ (12%) (red). An 11% increase in the width of the vibrational peak at 0.165 eV [18] is taken into account.

Figure 3

(a) Time evolution of $\mathrm{\Delta }R/R$ at $t_d<150\mathrm{fs}$ measured by a 7-fs pulse. (b) Time evolutions of $\mathrm{\Delta }R/R$ measured at (i) 0.85, (ii) 0.73, and (iii) 0.62 eV.

Figure 4

$\mathrm{\Delta }R/R$ spectra at various time delays $t_d=0–80\mathrm{fs}$ are shown as the circles. The blue-dashed, red-dashed, and orange curves indicate the calculated spectral change using the Lorentz model (orange), the spectral change calculated with only $-\mathrm{\Delta }{\omega }_p/{\omega }_p$ (blue-dashed), and that with only $\mathrm{\Delta }\gamma /\gamma$(red-dashed). The arrows indicate $\hslash {\omega }_p$.

Figure 5

(a) Time profiles of $-\mathrm{\Delta }{\omega }_p/{\omega }_p$ (blue dots) and $\mathrm{\Delta }\gamma /\gamma$(red dots) obtained using Lorentz analysis (shown by the blue-dashed and red-dashed curves in Fig. 4). (b) The time profile of the difference between the observed and calculated reflectivity changes at 0.73 eV ($\delta$).

Figure 6

Calculated time evolutions of six-lattice-spacing-distant off-diagonal density $-{\sum }_{\sigma }\langle c_{0\sigma }^{†}{c}_{6\sigma }+c_{6\sigma }^{†}{c}_{0\sigma }\rangle$ as an index of the delocalized nature of charges for $(U/t_2,V/t_2)=(0,0)$ (black), (1.0,0.55) (red line), and (2.0,1.1) (blue line). Schematic illustration of the CO molecular stack along the $a$ axis is also shown.