Abstract
Nonequilibrium pump-probe time domain spectroscopies can become an important tool to disentangle degrees of freedom whose coupling leads to broad structures in the frequency domain. Here, using the time-resolved solution of a model photoexcited electron-phonon system we show that the relaxational dynamics are directly governed by the equilibrium self-energy so that the phonon frequency sets a window for "slow" versus "fast" recovery. The overall temporal structure of this relaxation spectroscopy allows for a reliable and quantitative extraction of the electron-phonon coupling strength without requiring an effective temperature model or making strong assumptions about the underlying bare electronic band dispersion.
Highlights
Pump-probe spectroscopies offer the exciting opportunity to perturb and measure electrons and collective modes in solids on their intrinsic ultrafast time scales
We show how the time (t), momentum (k), and energy (!) resolution provided by state-of-the-art tr-Angle-resolved photoemission (ARPES) [25,26,27,28,37,38,39,40,41,42,43,44,45,46,47] experiments, in conjunction with the dependence of extracted decay times on the initial-equilibrium sample temperature, provides a direct method to measure the dominant phonon energy and electron-phonon coupling
The central result of this paper is that equilibrium ideas can be used to understand the nonequilibrium dynamics of a pumped system
Summary
Pump-probe spectroscopies offer the exciting opportunity to perturb and measure electrons and collective modes in solids on their intrinsic ultrafast time scales They provide a tool to gain insight into the behavior of matter pushed out of its thermodynamic equilibrium state, thereby probing microscopic details of complex manybody systems beyond effective thermodynamic variables. We address these issues by showing a full nonequilibrium solution of a generic electron-phonon-coupled model system and by relating the temporal spectroscopic response to microscopic quantum-many-body details of the system. We utilize this concept as a basis to directly access the intrinsic decay rates of quasiparticles in the time domain without assumptions about bare-band quantities that are needed in the frequency domain. Additional considerations regarding the trade-off between time and energy resolution, the breakdown of an effective temperature description, the connection between relaxation rates and the self-energy, and the additional effect of including electron-electron scattering are provided in Ref. [48]
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