Magneto-Optics and Non-Linear Spectroscopy Group: Research Topics

We aim at discovering and developing new mechanisms for manipulating the optical, magnetic and transport properties of matter. Fast magnetic state manipulation requires access to the ultra-short (sub-nanosecond) time scale, because this is the characteristic time scale involved. For example, the precession period of an electron spin in a magnetic field of 1 Tesla is 35.7 picoseconds (1 picosecond=1 trillionth of a second). We use picosecond and femtosecond light pulses to induce changes in the magnetic and optical properties of solids, and to monitor these properties as they evolve in time, with femtosecond resolution. Our experiments are firmly backed by theoretical models for light-matter interaction and many-body systems, which we develop using quantum mechanics and statistical physics. We focus, in particular, on yet unexplored mechanisms by which illumination influences magnetic order. Recently, we discovered surprising and spectacular new phenomena in antiferromagnetic EuSe, where using light we converted a zero-magnetization state into a saturated ferromagnet in 50 trillionths of a second. We demonstrated that in EuSe the absorption of a single photon flips the spin of nearly six thousand electrons (publication here). In EuS, a single photon orchestrates an even larger number of spins, nearly 20,000 (publication here and here). Our discoveries pave a novel path for ultrafast switching of the magnetic state of matter using few photons. Work funded by FAPESP, CNPq, NAP/USP, CAPES.

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