Davide Bossini
The wildly growing field of antiferromagnetic spintronics is currently addressing several fundamental questions. A major topic of investigation concerns the generation and manipulation of coherent magnons on the ultrafast timescale. The development of novel pulsed-laser sources has enabled scientists to address the following scientific question: which magnetic excited state can be induced by resonantly drive coherent magnons throughout the Brillouin zone? In my talk I will outline our approach to this open issue, which relies on the resonant drive of pairs of high-energy magnons in the weak ferromagnet α-Fe2O3, with wavevector near the edges of the Brillouin zone. This unprecedented concept results in strongly perturbing the entire magnetic system of the material, in particular: i) magnon modes with different wavevectors are excited and amplified; ii) the eigenfrequencies of magnons are modified; iii) a coupling between magnon modes is observed. Our results effectively report a femtosecond modification of the magnonic dispersion relation of α-Fe2O3 which, de facto, means transforming the system into a different magnetic material in the transient state, in which the magnetic interactions are changed by several percent of their ground-state values. These groundbreaking observations are rationalised in view of a resonant impulsive stimulated Raman scattering mechanism. The perspective of our results in terms of femtosecond coherent magnonics will be discussed.