Spin states of the first four holes in a silicon nanowire quantum dot.

We report measurements on a silicon nanowire quantum dot with a clarity that allows for a complete understanding of the spin states of the first four holes. First, we show control of the hole number down to one. Detailed measurements at perpendicular magnetic fields reveal the Zeeman splitting of a single hole in silicon. We are able to determine the ground-state spin configuration for one to four holes occupying the quantum dot and find a spin filling with alternating spin-down and spin-up holes, which is confirmed by magnetospectroscopy up to 9 T. Additionally, a so far inexplicable feature in single-charge quantum dots in many materials systems is analyzed in detail. We observe excitations of the empty quantum dot, which cannot correspond to electronic or Zeeman states. We show that the most likely explanation is acoustic phonon emission to a cavity between the two contacts to the nanowire.