Abstract
The state and evolution of planets, brown dwarfs and neutron star crusts is determined by the properties of dense and compressed matter. Due to the inherent difficulties in modelling strongly coupled plasmas, however, current predictions of transport coefficients differ by orders of magnitude. Collective modes are a prominent feature, whose spectra may serve as an important tool to validate theoretical predictions for dense matter. With recent advances in free electron laser technology, X-rays with small enough bandwidth have become available, allowing the investigation of the low-frequency ion modes in dense matter. Here, we present numerical predictions for these ion modes and demonstrate significant changes to their strength and dispersion if dissipative processes are included by Langevin dynamics. Notably, a strong diffusive mode around zero frequency arises, which is not present, or much weaker, in standard simulations. Our results have profound consequences in the interpretation of transport coefficients in dense plasmas.
Highlights
The state and evolution of planets, brown dwarfs and neutron star crusts is determined by the properties of dense and compressed matter
Once one identifies the random force with dynamic electron–ion collisions, the changes in the dynamic structure factor (DSF) we report here allow for assessing the strength of such collisions determining many transport and relaxation phenomena, a long standing problem in the warm dense matter (WDM) regime
Our results demonstrate the importance of properly including all effects randomizing the ionic motion when considering dynamic properties with molecular dynamics (MD) simulations in the WDM regime
Summary
The state and evolution of planets, brown dwarfs and neutron star crusts is determined by the properties of dense and compressed matter. The resulting diffusive process creates a zero-frequency mode and its strength may serve as an estimate of the effects of randomization processes This approach has previously been successfully implemented in the field of dusty plasmas to model the effects of neutral species on the diffusion coefficient[1,2,3]. The experimental possibilities to diagnose dense matter are rather limited and a thorough comparison of simulations and data is often the only way to reveal the microscopic behaviour Modelling matter in this parameter regime is very challenging as one often encounters systems with strong interactions as well as electrons that exhibit distinct quantum behaviour. This behaviour makes the ion modes very interesting as they encode almost the entire system behaviour including electron properties[19]
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