Abstract

Although there have been a number of theoretical and experimental investigations of the liquid state of carbon¹-⁵, there remains fundamental disagreement about its material properties, particularly its electrical properties. Is liquid carbon metallic or insulating? Transient electrical conductivity measurements¹ and melt-depth analysis of graphite excited by 30 ns laser pulses^2, as well as first-principles molecular dynamics calculations³ suggest that the liquid phase of carbon is metallic. The claim for an insulating liquid phase is based on picosecond optical reflectivity measurements⁴ which show decreased surface reflectivity for the liquid phase when excited above a well-defined melting threshold. We have recently reported the first time-resolved femtosecond reflectivity measurements performed on highly oriented pyrolytic graphite (HOPG) in which both metallic (Δt < 10 ps) and insulating (Δt > 10 ps) behaviors were observed⁵.

© 1990 Optical Society of America