Stability of Surface State Electrons on Helium Films
Electrons on helium substrates form a model Coulomb system in which the transition from classical electron liquid to Wigner crystal is readily observed. However, attempts to increase the electron density in order to observe the ‘quantum melting’ of the system to a Fermi degenerate gas are hindered by an instability of the helium surface. Here we describe experimental efforts to reach the degenerate regime on thin helium films and microstructured substrates, for which the surface instability is suppressed. We demonstrate that, although the electron densities obtained exceed those for bulk helium substrates, observation of quantum melting remains challenging. We discuss possible solutions to the technical challenges involved.
KeywordsElectrons on helium Thin films Quantum melting
This work was partly supported by JSPS KAKENHI Grant No. 24000007, and by the Taiwan Ministry of Science and Technology (MOST) through the MOE ATU Program and Grant Nos. NSC 102- 2112-M-009-015 and MOST 103-2112-M-009-017. We thank A. Dahm for helpful discussion and J. Engelhardt for contributions to the experiments.