Single-state measurement of the electrical conductivity of warm dense gold

Summary form only given. The regime of warm dense matter has emerged as an interdisciplinary field which has drawn broad interest from researchers in plasma physics, condensed matter physics, high pressure science, astrophysics, inertial confinement fusion, as well as material science under extreme conditions. However, single-state experimental data for the direct test of theoretical models within this regime has been scarce. We have performed experiments utilizing a femtosecond laser pump-probe technique to create and examine single states of warm dense matter. The isochoric heating of ultrathin (30 nm) freestanding, gold foils yielded uniform, solid-density states with energy densities up to 20 MJ/kg. The AC conductivity of such states was determined from reflectivity and transmission measurements of a femtosecond probe as a direct benchmark for transport theory. In addition, the observed time history of probe reflectivity and transmission led to the discovery of a quasi-steady-state behavior of the heated sample that suggested the existence of a metastable, disordered phase prior to the disassembly of the solid induced by ultrafast heating.