Isochoric, isobaric and ultrafast conductivities of aluminum, lithium and carbon in the warm dense matter (WDM) regime

Abstract

We study the conductivities $σ$ of (i) the equilibrium isochoric state ($σ_{\rm is}$), (ii) the equilibrium isobaric state ($σ_{\rm ib}$), and also the (iii) non-equilibrium ultrafast matter (UFM) state ($σ_{\rm uf}$) with the ion temperature $T_i$ less than the the electron temperature $T_e$. Aluminum, lithium and carbon are considered, being increasingly complex warm dense matter (WDM) systems, with carbon having transient covalent bonds. First-principles calculations, i.e., neutral-pseudoatom (NPA) calculations and density-functional theory (DFT) with molecular-dynamics (MD) simulations, are compared where possible with experimental data to characterize $σ_{\rm ic}, σ_{\rm ib}$ and $σ_{\rm uf}$. The NPA $σ_{\rm ib}$ are closest to the available experimental data when compared to results from DFT+MD, where simulations of about 64-125 atoms are typically used. The published conductivities for Li are reviewed and the value at a temperature of 4.5 eV is examined using supporting X-ray Thomson scattering calculations. A physical picture of the variations of $σ$ with temperature and density applicable to these materials is given. The insensitivity of $σ$ to $T_e$ below 10 eV for carbon, compared to Al and Li, is clarified.