Disk-shaped electronic bubbles in gaseous helium

The structure of 2D anions placed on a hydrogen substrate in the presence of gaseous helium is discussed. It is shown that these structures, shaped like quasi-two-dimensional disks, are created in a threshold-like manner in the vicinity of critical density n_c∼10²⁰ cm⁻³, which is appreciably lower than the critical density for the appearance of spherical electronic bubbles in gas and linearly depends on temperature. Experiment confirms the existence of such autolocalized states.