Speaker
Description
The Kagome lattice offers a plethora of interesting physics ranging from van-Hove singularities to Dirac points and flat bands. In particular, the Kagome metals family AV3Sb5 (A=K, Rb, Cs) features an unconventional superconducting phase, coexisting with a parent charge density wave (CDW) phase. The origin of the CDW is still under debate. Moreover, this family exhibit a flat band below the Fermi level, which offers a unique platform for a highly correlated electronic subsystem. Carrying the hallmark of strong electron-electron interaction, this can give rise to many-body states as well as exotic topological effects. While many of such interactions are difficult to access in thermal equilibrium, a dynamical study after perturbing the system promises additional insights into the nature of such states, and allows disentangling the different interactions at play. Interestingly, studies of flat band dynamics are scarce, and little is known on their response to ultrafast excitation.
In order to provide insight to these questions, we studied the ultrafast dynamics in CsV3Sb3 using time- and angle-resolved photoemission spectroscopy (trARPES). Starting in its CDW phase, we drive the system out of equilibrium and subsequently monitor the dynamics of the CDW gap around the Fermi level as well as the dynamics of the flat band. We discuss the ultrafast melting of CDW order, concomitant with a shift and a broadening of the flat band, all being modulated by various coherent phonon modes. While one prominent mode around 1.3 THz is clearly resolved in all bands, the flat band shows additional faster oscillations in the range of 4THz.
