Optical Conductivity and Photo-induced Polaronic Formation in Co2MnGa Topological Semimetal
The term polaron has been introduced by Salomon Pekar in 1946 to define a composite quantum object consisting of an electron or a hole dressed by a cloud of virtual phonons. The lattice polaron concept has been extended further to consider the coupling among an electron (or a hole) with others bosonic excitations like spin waves (magnetic polaron) to ultimately investigate more complex states in which electric charges form bipolaron or multipolaron quasi-particles [1]. Polarons have a profound impact to the equilibrium electric conductivity and optical properties of materials being at the basis of reduced charge mobility and metal-to-insulator transitions phenomena.
This paper [2] focuses instead on the non-equilibrium time-dependent properties of lattice polarons. We have observed a non-equilibrium polaron formation when electrons are photoexcited by a femtosecond light pulse (see the Figure) from the valence band to the conduction band of Co2MnGa Topological Semimetal. Excess electrons distort the underlying lattice and form polaron quasi-particle in a sub-ps time scale. The polaronic quasi-particle survives over hundreds of nanosecond propagating in the lattice and generating a metastable polaronic metallic state [2].
Authors: Luca Tomarchio, Salvatore Macis, Sen Mou, Lorenzo Mosesso, Anastasios Markou, Edouard Lesne, Claudia Felser, Stefano Lupi
Research Article: https://doi.org/10.1002/advs.202400247
Sapienza Terahertz: https://sites.google.com/uniroma1.it/sapienza-terahertz/home
[1] C.Franchini et al., Nature Review Materials 2023, https://doi.org/10.1038/s41578-021-00289-w
[2] L. Tomarchio et al., Advanced Science 2024, https://doi.org/10.1002/advs.202400247