Disorder induced loss of magnetization in Lieb's graphene quantum dots

The stability of the magnetization in Lieb graphene quantum dots (GQD) against disorder is studied. Such systems exhibit the degenerate shell of edge states in the middle of the energy gap occupied by spin polarized electrons. Disorder affects the energy spectrum and leads to the removal of the degeneracy, and in a consequence the loss of the magnetization. We find that there is a critical value of disorder strength over which the magnetization starts dropping. We first consider GQDs with different shapes and edge termination and compare the effect of bulk and edge disorder. We find that edge disorder affects states in the vicinity of the Fermi level, while the bulk disorder affects also the states far away from it. We next focus on Lieb GQDs with a single zigzag edge. The stability of the ferromagnetic order against disorder strength is analyzed for structures with a different edge length. The probability of getting maximal spin polarization is determined.