Imaging quantum melting in a disordered 2D Wigner solid

Area of Science:

• Condensed Matter Physics
• Materials Science

Background:

• Electrons in 2D systems form Wigner crystals at low densities and Fermi liquids at high densities.
• An intermediate phase exists between these states, characterized by a strongly correlated liquid.

Purpose of the Study:

• To investigate the quantum melting of a disordered Wigner solid in bilayer molybdenum diselenide (MoSe2).
• To characterize the transition from a solid to a liquid phase in this 2D electron system.

Main Methods:

• Utilized noninvasive scanning tunneling microscopy (STM) for imaging.
• Observed nanocrystalline domains and their behavior under varying densities.

Main Results:

• Wigner solids formed nanocrystalline domains pinned by disorder at low densities.
• Observed quantum densification within the solid phase.
• Identified a critical density where the Wigner solid melts locally, forming a mixed solid-liquid phase.
• Liquid regions expanded and formed a percolation network at higher densities.

Conclusions:

• The study provides direct observation of the quantum melting process in a 2D Wigner solid.
• The findings elucidate the complex phase transitions in strongly interacting 2D electron systems.