Inducing new states of matter in real and artificial solids using Floquet engineering
Dr. Gregor Jotzu, Max Planck Institute for the Structure and Dynamics of Matter, Hamburg
Leuchs-Russell Auditorium, A.1.500, Staudtstr. 2
A system that is periodically driven may behave quite differently than its static counterpart. In cases where the dynamics of the system is purely unitary, Floquet theory can provide exact results for an effective static Hamiltonian. This "Floquet Hamiltonian," may feature strongly renormalized parameters, such as an infinite or negative effective electron mass. However, entirely new terms may also appear, and it is even possible to induce a topologically non-trivial effective band structure in a trivial static system. I will show how circular driving of a honeycomb lattice leads to a topological transition and allows for a direct realization of Haldane's model when the driving frequency is sufficiently high. Experimentally, these effects can be very clearly observed by probing ultracold Fermions trapped in an optical lattice. Implementing a similar protocol in a real solid does however pose significant theoretical and experimental challenges. I will show that, despite the presence of dissipation and the low driving frequencies employed, a Floquet Hamiltonian successfully describes the dynamics of Graphene driven with mid-infrared laser pulses. Probing the appearance of the predicted light-induced anomalous Hall effect is made possible by detecting the transverse conductance with optically triggered witches on a picosecond time scale. By scanning the Fermi energy, the Floquet band structure is revealed in transport measurements. I will also present ongoing and future efforts to induce and control effects such as superconductivity and quantum magnetism by illuminating solids with strong laser pulses. One key requirement in this context consists in extending the arsenal of observables that operate on an ultrafast time scale.