Polaron transition of surface electrons on liquid He-4 films in zero and quantizing magnetic fields

Surface electrons (SE) prepared on helium films of thickness d are supposed to undergo a transition to the polaronic state when the corresponding binding energy lambda(b) similar to d(-4) is close to or larger than k(B)T. Although the polaron has been observed recently, no clear transition was seen so far. In this paper we want to present magnetotransport measurements carried out at rather high temperatures (T > 1.2 K) to avoid the Wigner crystallization for a wide range of electron densities (5 x 10(8) cm(-2) < n(e) < 7 x 10(9) cm(-2)) showing this transition to the polaronic state: The experimental evidence is demonstrated in zero-field mobility measurements versus d and also shown in the corresponding magnetotransport measurements up to 10T below and above the transition. (C) 1998 Elsevier Science B.V. All rights reserved.