Eur. Phys. J. B (2016) 89: 172
https://doi.org/10.1140/epjb/e2016-70149-8

Regular Article

Finite-temperature Wigner solid and other phases of ripplonic polarons on a helium film

¹ TQC, Universiteit Antwerpen, Universiteitsplein 1, 2610 Antwerpen, Belgium
² Lyman Laboratory of Physics, Harvard University, Cambridge, MA 02138, USA
³ Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, 2020 Antwerpen, Belgium

^a e-mail: jacques.tempere@uantwerpen.be
^b e-mail: vyacheslav.misko@uantwerpen.be

Received: 7 March 2016
Received in final form: 25 April 2016
Published online: 1 August 2016

Abstract

Electrons on liquid helium can form different phases depending on density, and temperature. Also the electron-ripplon coupling strength influences the phase diagram, through the formation of so-called “ripplonic polarons”, that change how electrons are localized, and that shifts the transition between the Wigner solid and the liquid phase. We use an all-coupling, finite-temperature variational method to study the formation of a ripplopolaron Wigner solid on a liquid helium film for different regimes of the electron-ripplon coupling strength. In addition to the three known phases of the ripplopolaron system (electron Wigner solid, polaron Wigner solid, and electron fluid), we define and identify a fourth distinct phase, the ripplopolaron liquid. We analyse the transitions between these four phases and calculate the corresponding phase diagrams. This reveals a reentrant melting of the electron solid as a function of temperature. The calculated regions of existence of the Wigner solid are in agreement with recent experimental data.