Quasiparticle Interference on a natural mineral: Mapping the bands of argentiferous Galena

Galena (PbS) is the main ore of lead, and in the early days of wireless technology, it played a fundamental part in crystal radios. High-quality samples, that cleave perfectly, are common natural occurrences. It belongs to the lead chalcogenides PbX (X=Te, Se, S), narrow direct bandgap semiconductors which have high thermoelectric figures of merit and unusual semiconducting properties. Their electronic band structure has been studied theoretically and experimentally, revealing a bandgap which decreases with decreasing temperature and under pressure.

Previous Scanning tunnelling microscopy (STM) studies on PbS crystals reported atomically-resolved surfaces. In this study, a natural argentiferous PbS crystal (Ag impurities, p-doped) was cleaved in situ and measured at 20K, using a home-built low-temperature STM. We observe high-quality surfaces with a large variety of defects, surrounded by clear patterns due to quasiparticle interference (QPI). We will show results from QPI to map its electronic structure in the occupied and unoccupied states.