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
This thesis presents the characterization of a broadband radio frequency power detector, they key element of the detector being the Herotek DZM020BB diode. The detector has been developed to...Show moreThis thesis presents the characterization of a broadband radio frequency power detector, they key element of the detector being the Herotek DZM020BB diode. The detector has been developed to measure shotnoise signal orig- inating from a UHV low temperature STM tunnel junction. The detector provides fast measurement times of 1 sec while providing enough resolu- tion 0.06μVrms to distinguish between different noise voltages. This detec- tor has been compared to the Zurch MFLI lock in amplifier which measures the shotnoise with measuring times in the order of 10 seconds. Systematic effects in the detector have been studied and possible solutions were sug- gested to eliminate these effects.Show less
In this thesis we discuss the results of different resonant circuits to measure shot noise in an STM. We found two circuits where a change in the shot noise can be detected relatively easily. One...Show moreIn this thesis we discuss the results of different resonant circuits to measure shot noise in an STM. We found two circuits where a change in the shot noise can be detected relatively easily. One of the circuits has a relatively large bandwidth and the other has a relatively large total signal. Furthermore we benchmarked an RF diode detector (envelope detector) to improve the measurement speed for shot noise measurements. We conclude that we need an additional amplifier to amplify the RF output signal of the resonant circuit $2\cdot 10^6$ to $3\cdot 10^6$ times to use the RF diode detector.Show less
