Nonequilibrium electron dynamics in pump-probe spectroscopy: Role of excited phonon populations

Abdurazakov, Omadillo; Nevola, D.; Rustagi, Avinash; Freericks, J. K.; Dougherty, Dan; Kemper, A. F.

doi:10.1103/physrevb.98.245110

Cited by 17 publications

(11 citation statements)

References 58 publications

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“…However, recent experimental and theoretical works have evidenced that ultrashort laser pulses induce strong out-of-equilibrium dynamics that cannot be described by simplified thermal models in the subpicosecond time regime [10,22,23]. As a consequence, a large number of theoretical and experimental studies have tried to shine light on the laser-induced out-of-equilibrium dynamics [24][25][26][27][28][29][30][31][32][33][34]. New theoretical models have been derived to improve the modelling on ultrashort timescales.…”

Section: Introductionmentioning

confidence: 99%

Theory of out-of-equilibrium electron and phonon dynamics in metals after ultrafast laser excitation

Ritzmann,

Oppeneer,

Maldonado

2019

Preprint

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The out-of-equilibrium dynamics of electrons and phonons upon laser excitation are often described by the two-temperature model, which assumes that both subsystems are separately in thermal equilibrium. However, recent experiments show that this description is not sufficient to describe the out-of-equilibrium dynamics on ultrashort timescales. Here, we extend and apply a parameterfree microscopic out-of-equilibrium model to describe the ultrafast laser-induced system dynamics of archetypical metallic systems such as gold, aluminum, iron, nickel, and cobalt. We report strong deviations from the two-temperature model on the picosecond timescale for all the materials studied, even for those where the assumption of separate thermal equilibriums seemed less restrictive, like in gold. Furthermore, we demonstrate the importance of the phonon-mode dependent electronphonon coupling for the relaxation process and reveal the significance of this channel in the lattice equilibration through an indirect coupling between phonons via the electronic system.

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Section: Introductionmentioning

confidence: 99%

Theory of out-of-equilibrium electron and phonon dynamics in metals after ultrafast laser excitation

Ritzmann,

Oppeneer,

Maldonado

2019

Preprint

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“…Our model also captures some salient aspects of fully quantum mechanical approaches such as the nonequilibrium Keldysh formalism, which encodes particle properties in propagators [36,52,53]. While these approaches are compelling, the calculations are complex and computationally taxing.…”

Section: Discussionmentioning

confidence: 99%

Establishing non-thermal regimes in pump-probe electron-relaxation dynamics

Na,

Boschini,

Mills

et al. 2020

Preprint

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Time-and angle-resolved photoemission spectroscopy (TR-ARPES) accesses the electronic structure of solids under optical excitation, and is a powerful technique for studying the coupling between electrons and collective modes. One approach to infer electron-boson coupling is through the relaxation dynamics of optically-excited electrons, and the characteristic timescales of energy redistribution. A common description of electron relaxation dynamics is through the effective electronic temperature. Such a description requires that thermodynamic quantities are well-defined, an assumption that is generally violated at early delays. Additionally, precise estimation of the non-thermal window -within which effective temperature models may not be applied -is challenging. We perform TR-ARPES on graphite and show that Boltzmann rate equations can be used to calculate the time-dependent electronic occupation function f ( , t), and reproduce experimental features given by non-thermal electron occupation. Using this model, we define a quantitative measure of non-thermal electron occupation and use it to define distinct phases of electron relaxation in the fluence-delay phase space. More generally, this approach can be used to inform the non-thermal-to-thermal crossover in pump-probe experiments.

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“…In the weak coupling regime, we consider the GW approximation for the self energy. This approximation has been used extensively for the realistic modeling of molecules, weakly correlated extended systems, coupling with bosonic excitations, and screening [32][33][34][35][36]42,43,90,91]. In combination with DMFT, it was used in and out of equilibrium to study plasmonic physics in correlated systems [30,44,[92][93][94][95].…”

Section: Correlated Metal Within Gwmentioning

confidence: 99%

“…Many have already reached the level of first-principles description [33][34][35][36][37]. The essential task is to evaluate the two-time Green's function either with a numerically exact method [38][39][40] or with a high-order approximation scheme adjusted for the problem being studied [17,30,[41][42][43][44][45][46][47][48][49].…”

Section: Introductionmentioning

confidence: 99%

Low rank compression in the numerical solution of the nonequilibrium Dyson equation

Kaye

Golež

2021

SciPost Phys.

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We propose a method to improve the computational and memory efficiency of numerical solvers for the nonequilibrium Dyson equation in the Keldysh formalism. It is based on the empirical observation that the nonequilibrium Green's functions and self energies arising in many problems of physical interest, discretized as matrices, have low rank off-diagonal blocks, and can therefore be compressed using a hierarchical low rank data structure. We describe an efficient algorithm to build this compressed representation on the fly during the course of time stepping, and use the representation to reduce the cost of computing history integrals, which is the main computational bottleneck. For systems with the hierarchical low rank property, our method reduces the computational complexity of solving the nonequilibrium Dyson equation from cubic to near quadratic, and the memory complexity from quadratic to near linear. We demonstrate the full solver for the Falicov-Kimball model exposed to a rapid ramp and Floquet driving of system parameters, and are able to increase feasible propagation times substantially. We present examples with 262 144 time steps, which would require approximately five months of computing time and 2.2 TB of memory using the direct time stepping method, but can be completed in just over a day on a laptop with less than 4 GB of memory using our method. We also confirm the hierarchical low rank property for the driven Hubbard model in the weak coupling regime within the GW approximation, and in the strong coupling regime within dynamical mean-field theory.

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Nonequilibrium electron dynamics in pump-probe spectroscopy: Role of excited phonon populations

Cited by 17 publications

References 58 publications

Theory of out-of-equilibrium electron and phonon dynamics in metals after ultrafast laser excitation

Theory of out-of-equilibrium electron and phonon dynamics in metals after ultrafast laser excitation

Establishing non-thermal regimes in pump-probe electron-relaxation dynamics

Low rank compression in the numerical solution of the nonequilibrium Dyson equation

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