23rd International Young Scientists Conference Optics and High Technology Material Science - SPO 2022 ONLINE "STAND WITH UKRAINE"

Generation and control of the Raman active phonon mode in Bismuth Telluride nanofilm with sub-picosecond THz radiation

24 Nov 2022, 17:00

15m

Hybrid (Taras Shevchenko National University of Kyiv and Shizuoka University)

Oral Light-matter interactions

Speaker

Dr Artem Levchuk (CEA PARIS-SACLAY, France)

Description

Intense picosecond terahertz radiation has opened new opportunities in solid-state physics and materials science, allowing to probe and/or control different degrees of freedom of a solid by driving electrons, magnons, or phonons at ultrafast timescales with an intense electric field associated with photon energy in the meV range¹. Owing to significant spectral weight in the terahertz (THz) frequency range and the momentum conservation, THz radiation can be directly coupled to high-frequency optical phonons (1-40 THz range), while other phonon modes can be also excited as a result of nonlinear interaction². However, despite numerous reports on optical phonon generation with THz light, there are still some debates on the driving optical phonon generation mechanisms, possibly originating from the non-linear ionic Raman scattering³ or THz sum frequency excitation⁴.

Here, we conduct an experimental study on a well-known thermoelectric compound and topological insulator, 16nm thick semimetal Bi₂Te₃ film, grown by the molecular beam epitaxy on the mica substrate. To study the coherent optical phonon dynamics, the sample was excited with pulsed, high-peak (up to 300 kV/cm) field THz radiation, and we measure the change in the 400 nm probe beam transmittance in a pump-probe geometry. In this work, we report the controlled excitation of 1.85 THz A¹_1g Raman active optical phonon with THz radiation having a central frequency in the range of 0.53-0.72 THz. From the notions of the transient phase and THz field strength – optical phonon amplitude dependence, we then try to identify the various pathways of the A¹_1g mode excitation with pulsed THz radiation.

Bibliography:
1. Kampfrath, T., Tanaka, K. & Nelson, K. A. Resonant and nonresonant control over matter and light by intense terahertz transients. Nat Photonics 7, 680–690 (2013).
2. Först, M., Mankowsky, R. & Cavalleri, A. Mode-Selective Control of the Crystal Lattice. Acc Chem Res 48, 380–387 (2015).
3. Melnikov, A. A. et al. Coherent phonons in a Bi2Se3 film generated by an intense single-cycle THz pulse. Phys Rev B 97, 214304 (2018).
4. Maehrlein, S., Paarmann, A., Wolf, M. & Kampfrath, T. Terahertz Sum-Frequency Excitation of a Raman-Active Phonon. Phys Rev Lett 119, 127402 (2017).