Stroboscopic Tests for Thermalization of Electrons in Pump-Probe Experiments.

Area of Science:

• Condensed matter physics
• Ultrafast spectroscopy
• Electron dynamics

Background:

• Pump-probe spectroscopy aims to understand electron relaxation dynamics after excitation.
• Assessing electron proximity to a thermal state using Fermi-Dirac distributions alone is difficult.
• Existing methods lack a direct measure of the distance from thermal equilibrium.

Purpose of the Study:

• To propose a novel method for quantifying the distance of electrons from a thermal equilibrium state.
• To introduce a comparison between effective fermionic and bosonic temperatures as a metric.
• To overcome limitations of solely fitting electron distributions to Fermi-Dirac functions.

Main Methods:

• Utilizing pump-probe spectroscopy to drive electrons out of equilibrium.
• Measuring effective fermionic temperatures via photoemission.
• Measuring effective bosonic temperatures (derived from fermions) via nonresonant Raman scattering.

Main Results:

• Demonstrated that effective fermionic and bosonic temperatures can be measured directly.
• Showed that the difference between these temperatures quantifies the deviation from thermal equilibrium.
• Established a new parameter to assess electron thermalization.

Conclusions:

• Comparing effective fermionic and bosonic temperatures provides a direct measure of electron thermalization.
• This approach offers a more accurate assessment of electron proximity to a thermal state than traditional methods.
• The proposed method enhances the understanding of electron relaxation dynamics in materials.