Zero field splitting of heavy-hole states in Ge quantum dots

Holes have gained increasing interest in the past few years as spin qubit candidates since their strong spin-orbit coupling allows full electrical control of the hole spins [1-4]. Despite the fact that a hole is simply a missing electron, their spins are behaving strikingly different than their electron counterparts. While the electron spin does not correlate with the direction of motion, for holes in semiconductors there is a strong coupling between the momentum and the hole pseudospin.
For heavy-hole (HH) states confined in two dimensions, the pseudospin points in the direction of strong confinement. This implies that such HHs should show a zero field splitting (ZFS). By performing cotunnelling spectroscopy, we measure a ZFS of up to 55μeV for the excited triplet states confined in a Ge hut wire quantum dot with an even hole occupation. The evolution of the triplet states both for perpendicular and parallel magnetic fields is in very good agreement with an anisotropic spin Hamiltonian.

Refecences:
1. C. Kloeffel et al., Phys. Rev. B. 97, 235422 (2018).
2. R. Maurand et al., Nature Com. 7, 13575 (2018).
3. H. Watzinger et al., Nature Com. 9, 3902 (2018).
4. N.W. Hendrickx et al., arXiv:1904.11443 (2019).