My research focuses on the ultrafast control of quantum materials
By applying high intensity electromagnetic pulses to materials, novel electronic phases with no equilibrium analog can be established and removed on picosecond timescales
Mathematically, the properties of such systems can be predicted using the Floquet formalism, which converts the time-dependent Schrödinger equation with a time-periodic Hamiltonian into an effective time-independent problem of diagonalizing a Hermitian operator in an extended Hilbert space
Of particular interest to us was the Floquet graphene antidot lattice (FGAL), which is a regularly hole-patterned graphene sheet subject to high intensity radiation as visualized below:
We found that while the equilibrium system is a standard semiconductor, the driven system can be a Dirac semimetal or a semi-Dirac semimetal, and even feature what we termed selective dynamical localization (SDL)
In order to connect with future experiments we established the optical conductivity fingerprints of each Floquet electronic phase using a Floquet generalization of linear response theory
Interestingly, the real part of the longitudinal conductivity can become negative (absolute negative conductivity): The material mediates a power transfer from the drive to the probe, which manifests as an unexpected enhancement of the reflectance
For technical reasons, the major benefit of driving the hole-patterned material is that the above bandwidth driving limit is reached with near-IR photon energies, which is about 20 times smaller than would be required for the pristine material
This also enables the same level of band renormalization to be achieved as the unmodified graphene sheet, but at orders of magnitude smaller intensities
If you want to learn more, please check out our papers from 2021 and 2023