In particular, identifying the thermalization and scattering pathways of ultrafast information transfer in these materials is critically important to overcome the performance limits of currently available devices. Therefore, special attention is being devoted to understanding the influence of the Rashba spin texture on the relevant scattering channels which determine the recombination time scales of photoexcited carriers in systems with a large Rashba parameter. A large Rashba effect is required for device miniaturization and to suppress spin randomizing scattering events known to occur in conventional semiconductors with small, or zero, Rashba splittings. In this context, optical excitation by femtosecond (fs)-laser pulses is an indispensable tool which could be utilized for more efficient and faster processing of spin information in future optical devices. Of particular interest is the understanding and exploration of nonequilibrium properties of Rashba systems and their nanostructures. A large Rashba effect is considered to be the key to achieving enhanced control of spin-polarized currents, efficient spin injection and spin-to-charge interconversion, large spin–orbit torques, and slow carrier recombination, as well as to realizing topological superconductivity and Majorana fermions, each distinct efforts in the multipronged approach toward the development of functional spintronic devices. As a result, the spin degeneracy of electronic states is lifted and their spin splitting becomes Δ E = 2α R| k|, which to first order depends linearly on momentum | k| and on the strength of the Rashba effect, as represented by the so-called Rashba parameter α R. The spin–orbit interaction can cause a large Rashba effect when an inversion asymmetry occurs at the surface or interfaces, or if it is present in the bulk. A central challenge is to exploit the spin–orbit interaction to achieve efficient processing and storage of information without external magnetic fields. Understanding the elementary scattering processes which underlie the relaxation of spin-polarized carriers in narrow-gap semiconductors with strong spin–orbit coupling is essential for future applications in spintronics. The present results are important for future applications of ferroelectric Rashba semiconductors and their excitations in ultrafast spintronics. These findings are supported by theoretical calculations within the Boltzmann approach explicitly showing the opposite behavior of all relevant electron–electron and electron–phonon scattering channels with temperature, thus confirming the microscopic mechanism of the experimental findings. It is demonstrated how, due to the Rashba effect, an interdependence of these timescales on the relative strength of both electron–electron and electron–phonon interactions is responsible for the counterintuitive temperature dependence, with spin-selection constrained interband electron–electron scatterings found both to dominate dynamics away from the Fermi level, and to weaken with increasing temperature. These dynamics exhibit an unconventional temperature dependence: while the cooling phase speeds up with increasing sample temperature, the opposite happens for interband thermalization. A complex thermalization pathway is observed, wherein three different timescales can be clearly distinguished: intraband thermalization, interband equilibration, and electronic cooling. 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. Particularly attractive is understanding and controlling nonequilibrium properties of ferroelectric Rashba semiconductors. A large Rashba effect is essential for future applications in spintronics.
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