T. Pietsch, E. Scheer, formerly H. Pernau and S. Egle,
This project deals with the transport properties of atomic bismuth contacts. We fabricate freestanding metallic bismuth nano-bridges by electron beam lithography and reactive ion etching. These bridges serve as the starting point for the formation of atomic-size and tunnel contacts by means of the mechanically controlled breakjunction technique. Since the bridges are broken in cryogenic vacuum, the contacts are free of oxygen or other contamination. The transport measurements are performed in a 3He cryostat and a dilution refrigerator in the temperature range from 0.01 K up to 2 K and in transverse magnetic fields up to 8 T.
Due to the extraordinary electronic structure of bismuth, many different effects can be observed. In particular, we are interested in the transmission channels and probabilities of a single atom bismuth contact. These are accessible to measurements by the analysis of IV characteristics in the superconducting state (multiple Andreev reflection).
We also observed magnetic transport properties, i.e. conductance fluctuations as a function of both magnetic field and bias voltage.
We found several hints to an atomic Bismuth conductivity of about 0.15 G0. The histogram in Fig. 1 shows conductance peaks at even multiples of 0.15 G0. Although the differential conductance versus field and bias voltage changes dramatical in this range. Fig. 2 shows such data at a zero field and zero voltage conductance of about 0.75 G0. At the moment our data serve as a starting point to detailed theoretical studies done in collaboration with the Universities of Karlsruhe and Madrid.