Dino Novko with our former PhD student Nina Girotto Erhardt and collaborators from University of Bordeaux, have published a paper in Physical Review Letters, where they demonstrated how electron-phonon interaction can be enhanced in photo-excited state in MoTe2.
This joint experimental and theoretical study combines two state-of-the-art approaches, i.e. timeresolved extreme ultraviolet momentum microscopy and constrained density functional perturbation theory (cDFPT), to demonstrate that the density of photoexcited carriers can serve as a tunable handle to modulate electron–phonon interaction under nonequilibrium conditions. By mapping transient band structures and analyzing valley-resolved electronic population dynamics in photoexcited 2H-MoTe2, we reveal pronounced band gap renormalizations and changes in carrier population lifetimes as a function of the light-induced carrier density. The microscopic origin of these renormalized nonequilibrium properties has been the subject of considerable debate. In this work, we resolve this controversy by clearly attributing both the band gap renormalizations and reduced lifetimes to dynamically renormalized electron–phonon coupling matrix elements.
From a theoretical perspective, our work introduces the dynamical renormalization of many-body coupling constants as a key element in understanding ultrafast thermalization processes- a feature often neglected in standard time-resolved techniques such as effective temperature models, timedependent Boltzmann equations, and non-equilibrium Green’s functions. This insight addresses a longstanding question in ultrafast materials science and paves the way for dynamically engineering quasiparticle interactions and emergent phases of matter via light–matter interactions, which are crucial for phenomena such as light-induced superconductivity and structural phase transitions.
Fig. 1: (a) Energy-momentum cut along the K-Σ-Γ high-symmetry direction, at pump-probe temporal overlap, using s-polarized IR pump and p-polarized XUV probe pulses, with arrows showing the direct (Δgd) and indirect (Δg i) band gaps. (b) Experimental and (c) theoretical photoexcited carrier density-dependent direct and indirect band-gap values. The dashed horizontal lines represent the associated band-gap values for which no photoexcited carrier screening of |g|2 is considered. (d) Time-resolved population dynamics in the K (blue) and Σ (red) conduction band valleys for two photoexcited carrier densities (2.7 × 1013 cm-2 and 7.8 × 1013 cm-2). (e) Valleyresolved photoexcited carrier density-dependent time constant as obtained in the experiment. (f) Theoretical single-particle electron lifetimes for various photoexcited carrier densities. The stars and dashed lines represent results obtained using equilibrium EPC matrix elements (eq. |g|2 ), while the filled circles and full lines show results of cDFPT calculations (including screening of EPC matrix elements by photoexcited carriers, exc. |g|2).
Read the full publication: doi.org/10.1103/dvlz-93t8