Ultrafast cooling and heating scenarios for the laser-induced phase transition in CuO

by Dr Johan Hellsvik (Department of Materials and Nano Physics, KTH)

Tuesday 23 May 2017, 11:00 → 12:00 Europe/Stockholm

112:028 (Nordita South)

We report theoretical modeling of the sub-picosecond magnetic phase transition which recently has been experimentally observed in optically pumped samples of multiferroic CuO. Intriguingly, different excitation mechanisms are found to drive distinct dynamics. Similar as in experiments and independently of the excitation mechanism, our multi-scale modeling shows that laser excitation of CuO can drive the spin system from the collinear ground state to the incommensurate multiferroic phase on a picosecond time scale. However, depending on the excitation mechanism, the transition proceeds either by heating up the spin system or by cooling it down, where the latter is a manifestation of an ultrafast magneto-caloric effect. In analogue with the ultrafast dynamics observed in ferrimagnetic rare-earth transition metal alloys, it is found that the time-scale of the observed dynamics is determined mainly by the strength of the exchange interactions.