Lightwave-control of the electron's charge, spin and valley pseudospin

by Mr Stefan Schlauderer (Universität Regensburg)

SR II+III ground floor (CFEL, Building 99)

SR II+III ground floor

CFEL, Building 99

In recent years, lightwave electronics has been developed as an ultimately fast way of controlling crystal electrons at the fundamental quantum level. Its conceptional idea is to use the oscillating carrier wave of intense light pulses to steer the translational motion of an electron faster than a single cycle of light. Despite being particularly promising information carriers, the internal quantum attributes of solids such as spin and valley pseudospin have not been switchable on the subcycle scale. In my talk, I will show how we exploit the carrier wave of intense terahertz (THz) pulses to control not only the electron’s motion in solids, but also its spin and valley pseudospin. The first subcycle angle-resolved photoemission study reveals how an intense terahertz field drives topologically protected Dirac currents on the surface of Bi2Te3 [1]. The inertia-free surface currents are protected by spin-momentum locking, giving a realistic parameter space for all-coherent lightwave-electronic devices. In the second set of experiments, I demonstrate a novel subcycle control scheme for the valley pseudospin in monolayer WSe2 [2], which opens a completely new toolbox for optical-cycle-scale quantum information technologies at room temperature. Finally, with the help of antenna-enhanced single-cycle terahertz transients, we can ballistically switch spins in antiferromagnetic TmFeO3 between metastable states separated by a potential energy barrier [3]. We directly trace the temporal and spectral fingerprints of this ultrafast and minimally dissipative dynamics.