Attosecond-resolved coherent control of zone-folded acoustic phonons in silicon carbide

TL;DR

The paper demonstrates attosecond-scale coherent control of zone-folded acoustic phonons in 4H-SiC by using a pair of phase-locked femtosecond pulses to coherently excite the FTA mode at ~6 THz and measure its dynamics via transient reflectivity. A density-matrix ISRS framework with two electronic levels describes the generation and interference of electronic and phonon pathways under off-resonant excitation, providing an analytic form for the coherent-control signal. The key result is a verified analytical expression for the phonon amplitude a) ⟨Q(t)⟩ ∝ sin(ωt − ωτ/2 + θ) with b) Q0 depending on pulse delay τ and phase, which explains the observed enhancement and suppression patterns. This work demonstrates attosecond-precision phonon control in a wide-bandgap semiconductor, with implications for ultrafast phononics and coherent manipulation of lattice dynamics in devices.

Abstract

Zone-folded acoustic phonons (6 THz) in 4H silicon carbide (SiC) have been coherently excited using a femtosecond near-infrared pulse and measured through transient reflectivity with a pump and probe protocol. Their amplitude is coherently controlled with 300-attoseconds precision and the results show interference fringe patterns due to electronic and phonon interference. The results are well reproduced by a model calculation with two electronic and phonon levels and an impulsive stimulated Raman process. Using the model, we obtain the analytical form of the coherent control scheme at an off-resonant condition.

Figures (7)

• Figure 1: (a) Intensity of the reflected probe pulse along a pump probe delay, and (b) its vertically enlarged spectrum.
• Figure 2: (a) The amplitude, and (b) the frequency obtained by curve fitting the transient reflectivity (shown in Fig. 1) with a sinusoidal function.
• Figure 3: Two-dimensional map of the transient reflectivity plotted against the pump-pump delay ($t_{12}$; vertical axis) and pump1-probe delay ($t_{13}$; horizontal axis).
• Figure 4: (a) Amplitude of the controlled oscillation after pump 2, (b) the optical interference, and (c) the FRAC against the pump-pump delay ($\tau$). The amplitude is normalized using that obtained after excitation after pump 1 only; oscillation between the irradiation timing of pumps 1 and 2.
• Figure 5: Phonon amplitude after pump 2 irradiation plotted against the pump-pump delay. (red curve (a)) experimental results, which is the same as in Fig. 4(a), and (blue curve (b)) simulation using equation (7) given in the text.