Conductive dense hydrogen

• M. I. Eremets
• & I. A. Troyan

• 
  

  Nature Materials

   

  10,

   

  927–931

   

  (2011)

  doi:10.1038/nmat3175

  Received

   

  27 May 2011

   

  Accepted

   

  18 October 2011

  Published online

   

  13 November 2011

  Molecular hydrogenis expected to exhibit metallic properties under megabar pressures. This metal is predicted to be superconducting with a very high critical temperature, T_c, of 200–400 K (ref. 1), and it may acquire a new quantum state as a metallic superfluid and a superconducting superfluid². It may potentially be recovered metastably at ambient pressures³. However, experiments carried out at low temperatures, T<100 K (refs 4, 5), showed that at record pressures of 300 GPa, hydrogen remains in the molecular insulating state. Here we report on the transformation of normal molecularhydrogen at room temperature (295 K) to a conductive and metallic state. At 200 GPa the Raman frequency of the molecular vibron strongly decreased and the spectral width increased, evidencing a strong interaction between molecules. Deuterium behaved similarly. Above 220 GPa, hydrogen became opaque and electrically conductive. At 260–270 GPa, hydrogen transformed into a metal as the conductance of hydrogen sharply increased and changed little on further pressurizing up to 300 GPa or cooling to at least 30 K; and the sample reflected light well. The metallic phase transformed back at 295 K into molecularhydrogen at  200 GPa. This significant hysteresis indicates that the transformation of molecular hydrogen into a metal is accompanied by a first-order structural transition presumably into a monatomic liquid state. Our findings open an avenue for detailed and comprehensive studies of metallic hydrogen.