Momentum gap states in transverse spectra in liquids

Transverse excitations in liquids have been a focus of intense research interests in recent years as they are closely related to macroscopic properties including heat capacity, thermal conductivity, and viscosity. Prior works have shown that rather than the transverse dispersion extending to k = 0, there exists a wavevector gap (k_gap) in liquids, now well-described by generalized hydrodynamics. However, finite widths at zero frequency in the momentum gap are still observed and the nature of these momentum gap states remains unexplored. In this work, we perform molecular dynamics on prototypical metallic liquids, Cu₅₆Zr₄₄ and Fe over a wide range of temperatures and find intimate relations between the widths of the momentum gap states and the diffusion coefficients over all temperatures studied. Our results, therefore, open novel prospects for understanding microscopic picture of transverse excitations in liquids.