Ultrafast Thermalization Pathways of Excited Bulk and Surface States in the Ferroelectric Rashba Semiconductor GeTe
Sprache des Titels:
Englisch
Original Kurzfassung:
A large Rashba effect is essential for future applications in spintronics. Particularly attractive is the study and control of nonequilibrium properties in ferroelectric Rashba semiconductors. Here, time? and angle?resolved photoemission is utilized to access the ultrafast dynamics of bulk and surface transient Rashba states after femtosecond?optical excitation of GeTe. A complex thermalization pathway is observed, wherein three different timescales can be clearly distinguished: (i) intraband thermalization, (ii) interband equilibration and (iii) electronic cooling. These dynamics are found to exhibit an unconventional temperature dependence: while the cooling phase speeds up with increasing sample temperature, the opposite happens for the interband thermalization. It is demonstrated how, due to the Rashba effect, an interdependence of these timescales on the relative strength of both electron?electron (e?e) and electron?phonon (e?ph) interactions is responsible for the counter?intuitive temperature dependence, with spin?selection constrained interband e?e scatterings found both to dominate dynamics away from the immediate vicinity of the Fermi level, and to weaken with increasing temperature. These findings are supported by theoretical calculations within the Boltzmann approach explicitly showing the opposite behavior of all relevant e?e and e?ph scattering channels with temperature, thus confirming the microscopic mechanism of the experimental findings. The present results are important for future applications of ferroelectric Rashba semiconductors and their excitations in ultrafast spintronics.
Forschungs-