Direct phase-sensitive identification of a d-form factor density wave in underdoped cuprates

Understand

The identity of the fundamental broken symmetry (if any) in the underdoped cuprates is unresolved.

• However, evidence has been accumulating that this state may be an unconventional density wave.
• Here we carry out site-specific measurements within each CuO$_2$ unit-cell, segregating the results into three separate electronic structure images containing only the Cu sites (Cu(r)) and only the x/y-axis O sites (O$_x$(r) and O$_y$(r)).
• Phase resolved Fourier analysis reveals directly that the modulations in the O$_x$(r) and O$_y$(r) sublattice images consistently exhibit a relative phase of ${\pi}$.