Speaker
Description
Many ordered physical systems are proximate to a low-energy competing phase. This can manifest as a roton-like feature within a dispersing collective mode. A paradigmatic example is the attractive Hubbard model with its superfluid ground state. Close to half-filling, it hosts a roton-like excitation associated with a competing charge density wave order. Inspired by pump-probe experiments, we explore a local density modulation that ‘pumps’ the charge density wave order. Using a dynamical simulation scheme that includes correlations at all scales, we find an enhanced response when the modulation frequency matches the roton gap. Resonant pumping leads to two propagation fronts. The first corresponds to an incoherent disturbance propagating radially outwards. It moves at a constant speed set by the sound velocity associated with the Goldstone mode of the superfluid. The second is a synchronization front, which defines a zone with coherent, dynamical charge density wave order. This zone expands with a radius that grows as the square root of time, akin to diffusive motion. The diffusion coefficient is set by the curvature of the collective mode around the roton minimum. Our results can be directly tested in ultracold atomic gases. They can motivate studies of dynamical ordering in solids, e.g., by optical pumping using a small spot-size laser or a terahertz STM.
| Keyword-1 | Propagation front |
|---|---|
| Keyword-2 | Competing orders |