A study was made of valley-polarized states in an armchair graphene quantum dot with double vacancy defects. Half-filled doubly degenerate states were found in the middle of the gap only when two vacancies occupy certain specific sites in each of the sublattices of the quantum dot. The doubly degenerate states forming around the vacancies were shown to be entirely localized in their respective sub-lattice, which results in that the two parallel-spin electrons in the degenerate Fermi level carry purely opposite valley pseudospins. Surprisingly, the pseudospin-degenerate states were found to be symmetric even when the reflection symmetry of the structure was broken by the vacancies. It was further shown that the pseudospin degeneracy, similar to the Kramer’s degeneracy lifted by a magnetic field, can be removed by an applied electric field. Like the Zeeman effect, the split states would retain their original valley pseudospins and exhibit linear splitting energy with respect to the applied field.

Abnormal Pseudospin-Degenerate States in a Graphene Quantum Dot with Double Vacancy Defects. A.Zhou, W.Sheng: Journal of Applied Physics, 2012, 112[1], 014308