Femtosecond quantum spin dynamics at the edges of the Brillouin zone in antiferromagnets
12.07.2017
| Date | 12.07.2017 |
|---|---|
| Time | 16:45-18:00 |
| Place |
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| Speaker | Davide Bossini |
| Area of expertise | Physics |
| Host | Dep. Physik |
| Contact | Johnson |
| Abstract | The investigation of the interaction between femtosecond laser pulses and magnetic materials has already revealed the tremendous potential of this approach for the ultrafast manipulation of spins[1,2]. In particular, the all - optical control of the magnetic order in antiferromagnets has become relevant, given the recent surge of interest in this class of materials for spintronics purposes. The peculiarity of l aser pulses, when compared to other stimuli, consists in the possibility to excite, manipulate and detect spin excitations on the femtosecond timescale which meets the requirement for ever - faster approaches to the control of magnets. However, the collectiv e spin excitations photoinduced hitherto in antiferromagnets are limited to low - wavevector magnons, which are the lowest - frequency modes in the dispersion of a typical antiferromagnet[1,3 - 5]. Recently the highest - frequency modes, which are magnons with wav evector near the edges of the Brillouin zone, have been impulsively photo - excited via a coherent light - scattering approach[6]. Remarkably, a complete manipulation of the phase and amplitude of coherent magnons with frequency equal to 22 THz and 1 nm wavele ngth (i.e. femto - nanomagnons ) was achieved[6]. Even more excitingly, further investigation of the femto - nanomagnonics regime demonstrated that it has little in common with the conventional spin dynamics triggered by nearly - zero - wavevector magnons . The classical thermodynamic concepts commonly employed in the description of magnetic dynamics critically do not hold in this newly discovered regime. This observation called for the development of a novel theoretical quantum - mechanical framework, based on magnonic coherent states. A proper equation of motion was derived within our model; in addition some intruiging predictions of our formalism suggest that the photo - generated magnons are intrinsically entangled[7]. |