Friedel oscillations as a probe of fermionic quasiparticles

Eugene Demler, Harvard University

Abstract:

When immersed in a sea of electrons, local impurities give rise to density modulations known as Friedel oscillations. In this talk I will review signatures of Friedel oscillations in STM and x-ray scattering experiments, focusing on the concrete example of cuprate superconductors. I will present a new approach to the analysis of Fourier-transformed STM images with subatomic resolution based on analysing overlaps between Fourier amplitudes that differ by reciprocal lattice vectors. The resulting holographic maps provide important information about the electronic structures of materials. When applied to superconducting cuprates this method solves a long-standing puzzle of the dichotomy between equivalent wavevectors. This analysis suggests that d-wave Wannier functions of the conduction band provide a natural explanation for experimental results that have been interpreted as evidence for competing unconventional charge modulations.