Imaging 2D Friedel oscillations in the interacting limit for monolayer WSe₂

Friedel oscillations in 2D Fermi liquids arise due to screening of charged impurities and provide a direct probe of electronic correlations. We have used scanning tunneling microscopy to image Friedel oscillations in a gate-tunable monolayer WSe₂ device as a function of carrier density and magnetic field at T = 4K. At low densities (n < 10¹² cm⁻²), the oscillation wavelength matches the periodicity of a Wigner crystal, while at higher densities it approaches the expected 2k_F wavelength for a Fermi liquid. For an applied perpendicular magnetic field, we observe strong enhancement of the Friedel oscillation amplitude for holes in the valence band, but no effect for electrons in the conduction band. We attribute this to the larger effective g-factor of the valence band. Our quantum Monte Carlo simulations suggest that this enhancement arises due to spin polarization of the hole Fermi liquid.