Aleksei Kimel
The ability to switch magnets between two stable bit states offers a natural and cheap means to store digital information. However, while recent developments in photonics enable nearly lossless data transfer with speeds exceeding 1 Tb/s, current magnetic data storage cannot keep up with these data-flow rates nor decrease energy dissipations. Reorientation of spin antiferromagnets can occur up to a 100 times faster than in their ferromagnetic counterparts. Moreover, the minima of the thermodynamic potential in antiferromagnets have absolutely equivalent energies, entropies and angular momenta, i.e. writing antiferromagnetic bits does not imply an irreversible transfer of energy or angular momentum between the lattice and the spins. Hence, antiferromagnets represent a highly-promising playground for the quest for the fastest and the least-dissipative mechanism of data storage.
How to control spins in antiferromagnets? Despite the 60-year long search for thermodynamic conjugates to the antiferromagnetic order parameter, efficient means to control antiferromagnetism are still being pursued. In my lecture, I am going to show that ultrashort pulses of electromagnetic radiation can become a game changer in the field. Starting from a simple theory I will show that even moderate, but rapidly varying magnetic fields can affect spins in antiferromagnets. Alternatively, using femtosecond laser pulses one can create non-equilibrium populations of specific electronic states, effectively change the orbital momenta and thus cause reorientation of spins especially in antiferromagnets. Moreover, ultrashort light pulses can induce coherent phononic states, modify the ground electronic state and also control spins via the spin-orbit interaction. It is especially intriguing that creating coherent magnonic or phononic state in antiferromagnets can substantially change the spectrum of the material making light-matter interaction essentially nonlinear. The lecture will be concluded with an outlook, where we will formulate the main challenges of ultrafast antiferromagnetism in the nearest future.