Wigner crystallization in a quasi-three-dimensional electronic system

Abstract

Application of extreme magnetic fields to a low-disorder 2D electron gas causes its electrons to reorder through an unexpected transition from a 2D to quasi-3D Wigner crystal state. When a strong magnetic field is applied perpendicularly (along z) to a sheet confining electrons to two dimensions (x–y), highly correlated states emerge as a result of the interplay between electron–electron interactions, confinement and disorder. These so-called fractional quantum Hall liquids1 form a series of states that ultimately give way to a periodic electron solid that crystallizes at high magnetic fields. This quantum phase of electrons has been identified previously as a disorder-pinned two-dimensional Wigner crystal with broken translational symmetry in the x–y plane2,3,4,5,6,7,8. Here, we report our discovery of a new insulating quantum phase of electrons when, in addition to a perpendicular field, a very high magnetic field is applied in a geometry parallel (y direction) to the two-dimensional electron sheet. Our data point towards this new quantum phase being an electron solid in a ‘quasi-three-dimensional’ configuration induced by orbital coupling with the parallel field.