Multiband topological phases of periodically kicked molecules

Special Quantum Seminar

Multiband topological phases of periodically kicked molecules

Volker Karle, Areg Ghazaryan, Mikhail Lemeshko

In this seminar Volker Karle will present our recent theoretical work on kicked molecules. We show that the simplest of existing molecules -- closed-shell diatomics not interacting with one another -- host topologically nontrivial phases when driven by periodic far-off-resonant laser pulses. A periodically kicked molecular rotor can be mapped onto a "crystalline" lattice in angular momentum space. This allows to define quasimomenta and the band structure in the Floquet representation, by analogy with the Bloch waves of solid-state physics. Applying laser pulses spaced by 1/3 of the molecular rotational period creates a lattice with three atoms per unit cell with staggered hopping, whose band structure features Dirac cones. These Dirac cones, topologically protected by reflection and time-reversal symmetry, are reminiscent of (although not equivalent to) the ones seen in graphene. They -- and the corresponding edge states -- are broadly tunable by adjusting the laser intensities and can be observed in present-day experiments by measuring molecular alignment and populations of rotational levels. This paves the way to study controllable topological physics in gas-phase experiments with small molecules as well as to classify dynamical molecular states by their topological invariants.