Figure 2

ERT electrical conductivity maps of sample S obtained with measurement protocols \({\mathcal {I}}_{{\mathrm {c}}}\) (constant current) and \({\mathcal {V}}_{{\mathrm {c}}}\) (constant voltage) at increasing excitation energy E. Maps \({\mathbf {A}}\) and \({\mathbf {C}}\) correspond to low sample excitation energy \(E < {55}\,\upmu \hbox {J}\), while maps \({\mathbf {B}}\) and \({\mathbf {D}}\) correspond to higher sample excitation energy \(E > {5.5}\,{\upmu \hbox {J}}\). Map difference \({\mathbf {B-A}}\) and \({\mathbf {D-C}}\) show the pixel-by-pixel absolute difference between the corresponding conductivity maps.