Fig. 6: Generation and detection of topological collective modes.
From: Probing light-driven quantum materials with ultrafast resonant inelastic X-ray scattering
a Circularly polarized pump pulses can drive bulk Dirac carriers (blue) and b open a gap at the Dirac points by breaking time-reversal symmetry. E and k denote energy and momentum of the band structure, respectively, whereas ωin stands for the incoming X-ray photon energy. In addition to the light-induced Floquet bandgap, the system exhibits chiral edge states (red) which give rise to dispersing collective modes in the time-resolved resonant inelastic X-ray scattering (trRIXS) spectrum c. These collective modes are linearly dispersing and only present at overlap with the pump excitation, unlike the particle-hole continuum owing to the bulk states. ω and q indicate energy loss and momentum transfer, whereas kF represents the Fermi wavevector.
