We report on magnetic resonance studies of high-density atomic hydrogen and deuterium in solid hydrogen matrices at temperatures below 1 K. Average concentrations of H atoms $\approx 3\times {10}^{19}{\mathrm{cm}}^{-3}$ are obtained in chemical tunneling reactions of isotope exchange with D atoms. The products of these reactions are closely located pairs of H atoms near ${\mathrm{D}}_2$ molecules with strong exchange interactions. We discovered a dynamic nuclear polarization effect on H atoms created by pumping the center of the H electron spin resonance spectrum, similar to the Overhauser effect in metals. Our results indicate that H atoms may be arranged inside molecular matrices at separations equivalent to local concentrations of $2.6\times {10}^{21}{\mathrm{cm}}^{-3}$. This opens up a way to build a metallic state of atomic hydrogen at zero pressure.

• Received 8 September 2014

DOI:https://doi.org/10.1103/PhysRevLett.113.265303