Jonathan Curtis- UCLA

Optical Control of Quantum Magnetism

New developments in intense infrared coherent light sources have enabled the generation of highly nonlinear dynamics in materials on ultrafast timescales, opening new avenues for the study and manipulation of quantum materials. Correlated magnetic insulators — materials in which the electronic charge is frozen but the spin still exhibits strong quantum fluctuations — often host a variety of interesting and potentially useful magnetic phases while also minimizing optical absorption, making them ideal candidates for optical control. Here I will present two such examples of how intense radiation can be used to induce nonequilibrium dynamics in these materials.

First, I will consider the multi-orbital Mott insulator YTiO3, which hosts fluctuating ferromagnetic order
within a quasi-degenerate orbital manifold. I will show how in the presence of strong terahertz radiation,
the nonequilibrium magnon dynamics in this system can be dramatically different from equilibrium due to
the presence of the multiple orbital states. In particular, by utilizing this orbital degeneracy, it is possible
to tune the magnon lifetime over an order of magnitude, allowing one to control the speed of
magnetization dynamics.
Second, I will consider the insulating cuprate compound Sr2Cu3O4Cl2 (2342) which hosts
two-dimensional spin-½ Neel order.Upon intense optical driving, ultrafast melting of the Neel order is
observed, with a dramatic resonant absorption occurring when the photon energy is twice the energy of a
Van Hove singularity in the magnon spectrum. I will show how this “bimagnon” absorption can be
understood as parametric driving of the spins by the optical electric field. This mechanism potentially
paves the way for optical generation of entangled magnon pairs, and is particularly interesting given the
relationship between spin fluctuations and high-temperature superconductivity seen in cuprates