Spatial Complexity Due to Incipient Electronic Nematicity in Cuprates
  Surface probes such as scanning tunneling microscopy (STM) have detected complex patterns at the nanoscale, indicative of electronic inhomogeneity, in a variety of high temperature superconductors. In cuprates, the pattern formation is associated with the pseudogap phase, a precursor to the high temperature superconducting state. Symmetry breaking (i.e. from C4 to C2) in the form of electronic nematicity has recently been implicated as a unifying theme of the pseudogap phase,[1] however the fundamental physics governing the nanoscale pattern formation has not yet been identified. Here we use universal cluster properties extracted from STM studies of cuprate superconductors in order to identify the fundamental physics controlling the complex pattern formation. We find that the pattern formation is set by a delicate balance between disorder and interactions, leading to a fractal nature of the cluster pattern. The method introduced here may be extended to a variety of surface probes, enabling the direct measurement of the dimension of the phenomenon being studied, in order to determine whether the phenomenon arises from the bulk of the material, or whether it is confined to the surface. 
B. Phillabaum, E. W. Carlson, and K. A. Dahmen
cond-mat.supr-con cond-mat.dis-nn cond-mat.stat-mech cond-mat.str-el