generated by the doping process, or by external probes which break the translational symmetry. Recent theoretical modelling has shown that several single-particle and two-particle experimental probes can be explained within a scenario where the underdoped superconducting region consists of a $d$-wave pair state coexisting with a local cluster spin glass phase driven by disorder. [@alvarez05; @andersen07; @atkinson07; @andersenkappa; @alvarez08]

Scanning tunneling microscopy/spectroscopy (STM/STS) measurements have provided a wealth of detailed local density of states (LDOS) spectra on the surface of [[Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ ]{}]{}(BSCCO), revealing an inhomogeneity in the spectral gap on the nanometer scale.[@cren; @howald; @pan; @lang] Furthermore, the differential conductance has been measured in the vicinity of Zn and Ni substituents for planar Cu.[@panzn; @lang; @hudson] Theoretically, the STS spatial conductance pattern produced by the magnetic Ni ion and its resonance energy of $\Omega_0\simeq \pm 10$ meV can be well described by a combination of potential and magnetic scattering,[@tangflatte] whereas no consensus has been reached about the proper explanation of the pattern around the Zn impurity, even though the local perturbation caused by the ion should in principle be simpler.[@balatsky; @vojta; @alloul; @andersen05]

One way to gain further insight into the nature of the physical state of small-gap versus large-gap 