Domain dynamics in thin solid films following ultrashort pulse excitation

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanoscale Dynamics

Background:

• Manganese arsenide (MnAs) epilayers on gallium arsenide (GaAs) serve as a model for studying strain effects.
• Epitaxial constraints significantly influence the dynamics of structural domains in thin films.
• Misfit strain and substrate-mediated elastic strain lead to spatially periodic domains between 10-42 °C.

Purpose of the Study:

• To investigate the effects of strain and epitaxial constraints on structural domain dynamics.
• To probe the time-resolved evolution of MnAs domains after ultrafast laser pulse excitation.

Main Methods:

• Utilized optical diffraction to observe domain evolution over seven orders of magnitude in time.
• Employed 150 fs pulse pumping to excite 150 and 190 nm thick MnAs films.
• Analyzed domain fractions and elastic strain dynamics as a function of time and temperature.

Main Results:

• Excitation induced oscillations in domain fractions and elastic strain with a ~400 ps period.
• Monotonous decrease in low-temperature phase fraction over ~2 ns, attributed to MnAs heat diffusion.
• Restoration of equilibrium structures occurred within 100 ns–2 μs via substrate heat diffusion.
• Transient periodic domains formed at temperatures as low as 4 °C after ~20 ns cooling.

Conclusions:

• Ultrafast laser excitation drives dynamic changes in MnAs structural domains and strain.
• Heat diffusion, both within the film and substrate, governs the relaxation dynamics.
• The study demonstrates the possibility of inducing transient ordered phases under specific cooling conditions.