The stabilization of high densities of atomic hydrogen $\left(2\times {10}^{19}{\text{cm}}^{-3}\right)$ embedded in solid ${\text{H}}_2$ films has been achieved by employing a method for producing the samples involving a direct dissociation of ${\text{H}}_2$ molecules by a cold plasma discharge in the sample cell at temperatures below 0.5 K. High stabilities against recombination were obtained. We observed density-dependent shifts and widths of the electron spin resonance lines resulting from the dipolar interactions between like and unlike spins. We discuss the possibilities for further increasing the H density and studying possible supersolid behavior.

• Received 9 April 2009

DOI:https://doi.org/10.1103/PhysRevB.79.220505