Events

Several insulating materials can be switched by laser pulses into transient metal states with apparently nonthermal properties. Often, this has been interpreted as a nonthermal closing of a Mott gap. An alternative mechanism is the generation of in-gap states by the nonthermal population of multiplets (e. g. singlet-triplet excitations in dimerized systems), or the nonthermal reshuffling of charge between orbitals. I will present recent nonequilibrium dynamical mean field theory studies of model systems, which provide insights into the nature of photo-induced nonthermal metal states in 1T-TaS2 and rare earth nickelates, and realistic simulations of the photo-induced dynamics in VO2, which clarify the excitation and charge reshuffling processes leading to the nonthermal monoclinic metal phase.

Strong light-matter interaction constitutes the bedrock of all photonic applications, empowering material elements to create and mediate interactions of light with light. Among others, phononamplified interactions were shown to bring a specific twist into this, in the infrared (IR) frequency range. Thus, phono-magnetic effects are the low-frequency analogues of inverse Faraday and Cotton-Mouton effects where phonons, not electrons, mediate the interaction between light and spins. In this case, light couples to the spins indirectly by exciting coherent vibrations of the crystal lattice (phonons) that transfer angular momentum to the magnetic ions. The optically driven chiral phonons in materials with strong spin-orbit coupling were shown to produce giant effective magnetic fields that exceed those previously seen by several orders of magnitude. The mechanism allows for bidirectional control of the induced magnetization through phonon chirality that in turn can be controlled by the polarization of the laser pulse.