Research to Produce Pressures of 600 GPa or Higher on Hydrogen and to Produce Metallic Hydrogen

Cornell University, Ithaca NY

Investigators

Abstract

This condensed matter physics project deals with molecular hydrogen subjected to ultrahigh pressures. The physical properties of hydrogen, one of the simplest elements or materials, are still not understood as a function of pressure. One fundamental question is whether it retains its insulating state or undergoes phase transitions to other, perhaps conducting or metallic states. One theory predicts a metallic transition near 450 GPa. Another theory suggests a transition to a near zero band gap semiconductor, near 400 GPa, subsequently converting to a cubic metal near 600 GPa. In previous work, the principal investigator has reached pressures of 560 GPa in other materials, but has been limited to 342 GPa in hydrogen, because hydrogen reacts with the diamond anvil cells required to reach ultrahigh pressures. A new hydrogen diffusion barrier has been developed that should reduce or eliminate this problem. Other technical advances, including reduction in the anvil tip diameter, suggest that the maximum attainable pressures may be increased by a factor of 1.4. Optical reflectivity measurements can be used to detect any transition to a semiconducting or metallic state. In addition, Meissner effect measurements will be made at pressure to detect a superconducting state. The research involves the training of post-doctoral associates in unique and cutting edge research techniques that will prepare the for careers in academe, industry and government. Hydrogen at ordinary pressures exists as a molecular gas, the molecule being formed by two hydrogen atoms held together by the prototypical chemical bond. However, this simple system contains much physics and is still not completely understood. One famous physicist, Victor Weiskopf, was quoted as saying, "we will not understand solid state physics until we understand solid hydrogen". Hydrogen can be cooled and compressed, first forming a liquid, and then a solid. It is these phases, particularly the solid phase that present considerable challenges to both theory and experiment to understand. The goal of this research is to use the latest diamond anvil techniques to achieve ultrahigh pressures to convert initially insulating solid hydrogen to a metallic, conducting state, and possibly even to a superconducting state. This will require reaching the unheard of static pressure of 600 GPa, which is far above the pressure at the center of the earth. It has been calculated that metallic hydrogen will be a superconductor with a very high Tc, possibly room temperature. This calculation has been given added credence by the recent findings of high Tc's in the low atomic number materials MgB2 at ambient pressure, and Li at high pressure. A discovery of superconductivity near room temperature in hydrogen would be a great stimulus to search for superconductivity in other low-Z materials. The research involves the training of post-doctoral associates in unique and cutting edge research techniques that will prepare them for careers in academe, industry and government.