Dresden 2020 – wissenschaftliches Programm
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SYAS 1.4: Hauptvortrag
Montag, 16. März 2020, 16:45–17:15, HSZ 02
All-coherent subcycle switching of spins by THz near fields — •Christoph Lange — Department of Physics, University of Regensburg, Regensburg, Germany
As state-of-the-art electronics encounters ultimate limits, novel concepts for harnessing coherent charge and spin dynamics in solid-state systems are being sought after. Atomically strong, phase-locked electromagnetic waveforms in the terahertz (THz) spectral range with photon energies far below typical interband excitations have facilitated lightwave acceleration of charges in bulk semiconductors, leading to dynamical Bloch oscillations and high-harmonics generation. Moreover, strong THz fields have driven inertia-free, ballistic currents of Dirac fermions of topological surface states of Bi2Te3 over mesoscopic distances, moving lightwave-electronic devices into practical reach. In contrast, subcycle control of the spin degree of freedom is much more challenging due to the intrinsically lower coupling of optical fields to magnetic excitations. We exploit a novel electric-dipole mediated mechanism to induce unprecedentedly large spin oscillations in the antiferromagnet TmFeO3. Strong, single-cycle THz pulses are enhanced by a custom-tailored, micrometer-sized metallic antenna fabricated on top of a bulk TmFeO3 sample, where the antenna’s atomically strong near fields change the magnetic anisotropy on a subcycle scale. The resulting spin dynamics include a characteristic phase flip, an asymmetric spectral splitting of the magnon resonance, and a long-lived offset of the polarization rotation signal, representing a novel fingerprint of all-coherent spin switching with minimal energy dissipation.