Event Details

We report on the experimental observation of two phases of hydrogen atoms in solid H2 films at temperatures 0.1 − 0.8 K, characterized by a large enhancement of the nuclear spin polarization compared to that given by Boltzmann statistics ( = 0.15 at = 0.15 K). The first phase with = 0.35(5) is formed spontaneously during sample storage in a high magnetic field ( = 4.6 T ). The second phase with an even higher nuclear polarization, = 0.75(7), can be achieved at ≤ 0.55 K by repeating sequences of Dynamic Nuclear Polarization followed by a system relaxation. Upon warming through the range 0.55 − 0.65 K the highly polarized phase undergoes a phase transition to the spontaneously polarized phase, which breaks down at ≈ 0.8 K and the nuclear polarization gradually converges to the Boltzmann distribution. We discuss possible scenarios for explaining the nature of the observed phenomena.