When cuprate compounds are sufficiently doped with extra holes, the Mott insulating phase gives way to the puzzling phenomenon of high-temperature superconductivity. Here, we use spectroscopic...Show moreWhen cuprate compounds are sufficiently doped with extra holes, the Mott insulating phase gives way to the puzzling phenomenon of high-temperature superconductivity. Here, we use spectroscopic-imaging scanning tunnelling microscopy (SI-STM) to probe two overdoped cuprate samples belonging to the family of BSCCO. The two samples have slightly different doping levels and critical temperatures TC of 3 K and 12 K. At this doping level, the band structure contains a saddle point close to the Fermi surface. As such, one expects to see a van Hove singularity (vHS) peak in the local density of states at every spatial position, i.e. in every STM dI/dV spectrum. Surprisingly, we find that the vHS peak is absent in part of the measured dI/dV spectra. Hence, to enable further investigation into the partial absence of the vHS peak, we developed a phenomenological model that is capable of fitting all the single dI/dV spectra. Using this model, we are able to spatially map the presence of the van Hove singularity and to correlate its energy to the width of the measured gap.Show less
