Prediction of a roton-type feature in warm dense hydrogen

In a recent Letter [T. Dornheim et al., Phys. Rev. Lett. 121, 255001 (2018)0031-900710.1103/PhysRevLett.121.255001], it was predicted on the basis of ab initio quantum Monte Carlo simulations that, in a uniform electron gas, the peak ω₀ of the dynamic structure factor S(q,ω) exhibits an unusual nonmonotonic wave number dependence, where dω₀/dq<0, at intermediate q, under strong coupling conditions. This effect was subsequently explained by the pair alignment of electrons [T. Dornheim et al., Commun. Phys. 5, 304 (2022)2399-365010.1038/s42005-022-01078-9]. Here we predict that this nonmonotonic dispersion resembling the roton-type behavior known from superfluids should be observable in a dense, partially ionized hydrogen plasma. Based on a combination of path integral Monte Carlo simulations and linear response results for the density response function, we present the approximate range of densities, temperatures and wave numbers and make predictions for possible experimental observations.