Skip to content

Manipulating polaron transport via laser-induced coherent phonons

Date:28-08-2023 Print

Polarons are the quasiparticles composed of excess electrons dressed with virtual phonon clouds. They are ubiquitous in materials, and play a key role in various physiochemical properties, including superconductivity, photocatalysis and ferroelectricity. However, carrier mobility is reduced when polarons are formed due to strong carrier localization, harming the performance of electrical devices, while the effective strategy to solve this problem is still lacking.

Ultrafast photoexcitation is an efficient method to manipulate the dynamics of (quasi)particles under non-equilibrium. However, most of previous ultrafast experiments were limited to characterize polaron formation process, and only speculations about polaron transport mechanism were presented. Theoretical studies based on the adiabatic approximation can only reveal the static and thermal-dynamics characteristics of polarons. Recently, WANG Huimin and LIU Xinbao et al. in Prof. MENG Sheng group from Institute of physics, Chinese Academy of Sciences have discovered that laser-driven coherent phonons enable order-of-magnitude enhancement of polaron mobility.

Wang et al. found that the selective excitation of specific vibrational modes effectively reduces the energy barrier of polaron hopping. Besides, due to the strong nonadiabatic couplings between electronic and ionic subsystem, phonon-phonon scattering in q space rapidly occurs within sub-picoseconds, which triggers the migration of polaronic deformations. The carrier mobility in the prototypical polaronic material Li2O2 can be increased by eight orders of magnitude by tuning laser parameters, much more efficient than thermal effects.

These results extend the understanding of polaron dynamics to the non-equilibrium regime. The non-thermal pathway for ultrafast control of polarons is proposed for the first time, which would innovate the design principles of optoelectronic devices with high on-off ratio and ultrafast responsibility.

The study entitled "Giant acceleration of polaron transport by ultrafast laser-induced coherent phonons" was published in Science Advances.The study was supported by the National Key Research and Development Program of China, the National Natural Science Foundation of China, and the Chinese Academy of Sciences.

Fig. 1. Laser-controlled polaron transfer and its potential applications. (Image by Institute of Physics)

Fig. 2. Effects of coherent phonon excitation on polaron transport. (Image by Institute of Physics)

Fig. 3. Nonadiabatic effect during polaron transfer. (Image by Institute of Physics)

Institute of Physics CAS
MENG Sheng

Key words:
Polaron transfer; Ultrafast photoexcitation; Coherent phonons; Non-adiabatic effect

Polaron formation severely hampers carrier transport for which effective controlling methods are urgently needed. Laser-controlled coherent phonon excitation enables orders of magnitude enhancement of polaron mobility, which would innovate the design principles of optoelectronic devices.