Warm Dense Matter - An Emerging Frontier in Plasma and Condensed Matter Science

Summary form only given. Warm Dense Matter is a name I used in 2000 to draw attention to the missing link between condensed matter and plasma physics, one that has broad relevance to other disciplines such as shock physics, material science, astrophysics, and Inertial Confinement Fusion science. By Warm Dense Matter I am referring to states with temperatures comparable to their Fermi energy, and densities that are sufficiently high that the Coulomb potential energy of interaction among ions exceeds their kinetic energy. Such a temperature-density condition brings to bear all the complexities including structural disorder, electronic excitation, electron degeneracy and ion-ion correlation. It renders conventional theories inadequate and Warm Dense Matter is a unique challenge and a new frontier in modern-day plasma and condensed matter science. This is also the temperature-density condition that places Warm Dense Matter in the region of the phase diagram that describes the transformation of a solid into a plasma, a process central to the production of laboratory high-energy-density plasmas using pulsed power or lasers. At LLNL, we have developed a unique approach of Isochoric Laser Heating for the production of well-defined Warm Dense Matter states. This has enabled us to obtain the first data on electrical conductivity, critical energy density for lattice disassembly, as well as intraband and interband transitions for warm dense gold at energy densities up to 10¹² J/m³. The results have far reaching significance including the impetus to advance condensed matter physics beyond the adiabatic approximation.