Scientists at the Paul Scherrer Institute PSI have shown that excitation of a spin liquid with intense THz pulses causes spins to appear and align within less than a picosecond. This induced coherent state causes a magnetic field to form inside the material, which is detected using ultrashort X-ray pulses at the X-ray Free Electron Laser SwissFEL.
Spins carried by atoms are the building blocks of magnetism. In a ferromagnet, they all align in the same direction, a feature used to store data on hard drives. In antiferromagnets, they form an antiparallel alignment. Like the surface of a stormy sea where water mountains build up here and there, disappearing as fast as they come, the spins in a spin liquid are fluctuating and form no ordered magnetic state despite local interactions.
Scientists at PSI have shown that the electromagnetic field of short THz pulses imprints its coherence onto the orbital wavefunctions of Terbium atoms of a Tb2Ti2O7 crystal, causing the spins of 1015 Tb excited ions in the material to appear and move synchronized, reminiscent of how wind can create highly periodic patterns of waves. This created state is called an ensemble of coherent quantum states.
Read more on PSI website
Image: Artistic impression of a magnetic moment appearing in a spin liquid after excitation with an intense short THz pulse
Credit: Roman Mankowsky.