Real-Time GW-Ehrenfest-Fan-Migdal Method for Nonequilibrium 2D Materials

Abstract

Quantum simulations of photoexcited low-dimensional systems are pivotal for understanding how to functionalize and integrate novel two-dimensional (2D) materials in next-generation optoelectronic devices. First-principles predictions are extremely challenging due to the simultaneous interplay of light–matter, electron–electron, and electron–nuclear interactions. We here present an advanced ab initio many-body method that accounts for quantum coherence and non-Markovian effects while treating electrons and nuclei on equal footing, thereby preserving fundamental conservation laws like the total energy. The impact of this advancement is demonstrated through real-time simulations of the complex multivalley dynamics in a molybdenum disulfide (MoS2) monolayer pumped above gap. Within a single framework, we provide a parameter-free description of the coherent-to-incoherent crossover, elucidating the role of microscopic and collective excitations in the dephasing and thermalization processes.

Ultrafast Nonadiabatic Phonon Renormalization in Photoexcited Single-Layer MoS2

“…Certain discrepancies in timescales between experiments and theoretical results obtained here could be attributed to the screening of the matrix element induced by the substrate . Note that the recent theoretical study based on nonequilibrium Green’s functions also found that the Γ- and K -point phonons are dominantly involved in nonequilibrium carrier dynamics in monolayer MoS 2 . Interestingly, they also show that the optical phonons participate more in the relaxation dynamics compared to the acoustic modes.…”

“…48 Note that the recent theoretical study based on nonequilibrium Green's functions also found that the Γand K-point phonons are dominantly involved in nonequilibrium carrier dynamics in monolayer MoS 2 . 125 Interestingly, they also show that the optical phonons participate more in the relaxation dynamics compared to the acoustic modes. The obtained relaxation rates around Γ, K, as well as M points are also significantly increased in time, where values at t = 2 ps are 4−5 times larger compared to the corresponding values at the initial time.…”

Nonadiabatic Molecular Dynamics with Non-Condon Effect of Charge Carrier Dynamics

“…However, there is still a significant gap in the development of comparable theoretical tools, especially for first-principles approaches. A case in point is the time-dependent density functional theory (TD-DFT) anchored nonadiabatic molecular dynamics (NA-MD), − which evolve the electron population on the MD trajectories computed with a single k-point in the momentum space subjected to electron transfers driven by electron–phonon couplings to maintain momentum conservation. The limitation inhibits exploration into nonradiative multiphonon transition assisted charge dynamics, such as intra- and intervalley scattering and indirect electron–hole recombination.…”

Semiconductor electron-phonon equations: A rung above Boltzmann in the many-body ladder

“…Through the GKBA for electrons and phonons the self-energies Σ GW,≶ (t, t ′ ), Σ FM,≶ (t, t ′ ) and Π ≶ (t, t ′ ) with t > t ′ become functionals of ρ < (t ′ ) and γ < (t ′ ) with t ′ < t. Therefore the GKBA equations ( 26) and ( 28) carry memory, i.e., the density matrices at time t depend on the history. This scheme has been recently implemented to study the relaxation of electrons and phonons in a photoexcited MoS 2 monolayer [64]. On the contrary the MGKBA leads to equations of motion with no memory since the self-energies become functionals of ρ < (t) and γ < (t).…”

“…These new features pave the way for first-principles studies of the coupling between coherent phonons and excitons as well as squeezed phonon states and time-dependent Debye-Waller factors. Whether the consistent treatment of phononic occupations and coherences has also an impact on the coherent-to-incoherent crossover [64,84] and on the thermalization of electrons and phonons remain to be seen case by case.…”