Jotzu, Gregor

Date:    Thursday, Dec 16, 2021
Time:   14:00
Place:   ETH Zurich, Campus Hönggerberg, HPF G 6
Host:    Tilman Esslinger

Controlling Quantum Materials using Periodic Driving: Topology, Superconductivity and Ultrafast Magnetic Field Control

Gregor Jotzu
Max Planck Institute for the Structure and Dynamics of Matter, CFEL, Germany

Periodically driving complex quantum systems can give access to novel states of matter and unlock new functionalities ultrafast timescales. In the controlled environment of optical lattices, this method has been very successful for “Floquet engineering” band structures, magnetic order or inducing non-trivial topology. Extending this approach to solids is challenging but very promising: In Graphene, we have induced a Haldane-type anomalous Hall effect using circularly polarized mid-infrared laser pulses. Probing it was accomplished by performing sub-picosecond transport measurements. Extending Floquet theory to include decoherence allowed for a successful theoretical description. Moving to strongly correlated systems, we have observed superconducting THz optical properties in certain organic superconductors when driven with strong mid-infrared lasers, well above the equilibrium Tc. We have used high-pressure techniques and magneto-thermoelectric measurements to further explore this mysterious phenomenon. The results suggest a crucial role of superconducting fluctuations above Tc – which may also explain the appearance of nanosecond metastability.

Does such a light-induced state also feature a Meissner effect? I will present a setup for performing sensitive, spatially resolved sub-picosecond magnetic field measurements to probe the magnetic properties of light-induced states. In addition, by disrupting supercurrents flowing in thin YBCO structures with laser pulses, ultrafast control of magnetic fields and gradients becomes possible. Beyond superconductivity, these methods open up a range of applications for systems including quantum magnets and topological edge states.