Quasiparticle dynamics and phonon softening in FeSe superconductors

Area of Science:

• Condensed matter physics
• Materials science
• Superconductivity

Background:

• Iron-based superconductors, such as iron selenide (FeSe), exhibit complex electronic properties.
• Understanding quasiparticle dynamics is crucial for elucidating the mechanisms behind superconductivity in these materials.

Purpose of the Study:

• To investigate the quasiparticle dynamics in FeSe single crystals.
• To explore the interplay between spin fluctuations, superconductivity, and phase transitions in FeSe.
• To determine the electron-phonon coupling constant and its implications for the superconducting mechanism.

Main Methods:

• Dual-color transient reflectivity measurements (ΔR/R) to probe ultrafast dynamics.
• Transport measurements to analyze electrical properties.
• Relaxation time analysis to identify phase transitions.

Main Results:

• The amplitude of the fast component in ΔR/R indicates a competition between spin fluctuations and superconductivity.
• Anomalous changes in relaxation time at 90 K and 230 K suggest structural phase transitions and potential new phase behaviors.
• The electron-phonon coupling constant (λ) was determined to be 0.16, matching theoretical predictions.

Conclusions:

• FeSe exhibits unconventional superconductivity, evidenced by a small electron-phonon coupling constant.
• The study identifies key phase transitions and dynamics influencing superconductivity in FeSe.
• Transient reflectivity is a powerful tool for understanding complex superconducting materials.