Accurate measurement of specific resistivity in low-resistance materials is a challenge due to the influence of parasitic resistances from the measurement leads and contacts. In this thesis, I describe the implementation, systematic evaluation, and application of the Van der Pauw method, which allows for precise measurements on samples of arbitrary shape. For this purpose, in the Laboratory for Electrical and Magnetic Measurements at the Faculty of Mathematics and Physics, University of Ljubljana, we developed and built a custom cable with a switchbox for the QD PPMS® 9T measurement system.
The system was first tested with measurements on samples made from aluminum foil. A baseline four-point probe measurement on a strip-shaped sample yielded a specific resistivity of ρ(300 K) = 3.1 ± 0.4 μΩ·cm, which is in agreement with literature values. This was followed by Van der Pauw method measurements on five samples of different geometries (square, circle, Greek crosses). The results confirmed the validity of the method, as all measurements yielded consistent values for specific resistivity, thereby demonstrating the method’s independence from sample shape.
I then used the validated measurement technique to investigate the superconducting properties of a niobium sample with a high residual-resistance ratio (RRR = 45.26). At zero magnetic field, I determined the critical temperature to be Tc = 9.250 K. With measurements in external magnetic fields up to 0.5 T, I observed the suppression of the critical temperature and successfully constructed the H-T phase diagram, which describes the boundary between the superconducting and normal conducting states. The work demonstrates the successful implementation of a reliable system for the characterization of electrical transport properties of materials.
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