Atomic hydrogen and ultra-cold plasmas

Two-dimensional Bose and Fermi gases

Spin-polarized atomic hydrogen adsorbed on the surface of liquid helium form a weakly interacting two-dimensional (2d) gas. Hydrogen is a bosonic atom and is prediced to undergo a  Kosterlitz-Thouless (KT) transition [1] to superfluidity when cooled to low temperature. Deauterium is simlar but being a Fermion it can be conrasted with its bosonic counterpart. The KT transition is accompanied by a transition that can be regarded as the two-dimensional analog of Bose-Einstein Condensation (2-d BEC). People have been aware of the possibility of the possibility of 2-d BEC in hydrogen right from the start of cold H research, but only since 1991 has it been actively analyzed (see e.g. [2]) and pursued experimentally by groups in the field. In 1998 the first experimental evidence was obtained for the existence of such a phase by a Finish-Russian collaboration [3]. In Amsterdam we study the adsorbate of H atoms on top of bulk helium using resonant fluorescence at the Lyman-alpha transition of the hydrogen atom [4] as well as in the deuterium atom [5]. In atomic hydrogen the 2-d gas is in equilibrium with a three dimensional gas above the surface that is so dense that photo-association, the formation of molecules mediated by light absorption, could be directly observed[6]


References

[1] J.M. Kosterlitz and D.J. Thouless,
Ordering, metastability, and phase transitions in two-dimensional systems,
J. Phys. C 6, 1181 (1973).

[1] B.V. Svistunov, T.W. Hijmans, G.V. Shlyapnikov, and J.T.M. Walraven,
Resonant light absorption and the problem of observing the Kosterlitz-Thouless transition in spin-polarized hydrogen adsorbed on a liquid-He surface,
Phys. Rev. B 43, 13412 (1991).

[2] A.I. Safonov, S.A. Vasiliev, I.S. Yasnikov, I.I. Lakashevich, and S. Jaakkola,
Observation of a quasi-condensate in two-dimensional atomic hydrogen,
Phys. Rev. Lett. 81, 4545 (1998).

[4] A.P.Mosk, M.W. Reynolds, T.W. Hijmans, and J.T.M. Walraven,
Optical excitation of atomic hydrogen bound to the surface of liquid helium,
Phys. Rev. Lett. 81, 4440-4444 (1998).

[5]    A.P.Mosk, M.W. Reynolds, and  T.W. Hijmans,
Atomic Deuterium adsorbed on the surface  of liguid helium,
Phys. Rev. A 64, 022901 (2001).

[6]    A.P.  Mosk, M.W. Reynolds, T.W. Hijmans, and J.T.M. Walraven,
Photoassociation of ultra-cold atomic hydrogen,
Phys. Rev. Lett 82 307-311 (1999).


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