Orbital ferromagnetism in interacting few-electron dots with strong spin-orbit coupling

Abstract

We study the ground state of $N$ weakly interacting electrons (with $N\le 10$) in a two-dimensional parabolic quantum dot with strong Rashba spin-orbit coupling. Using dimensionless parameters for the Coulomb interaction, $λ\lesssim 1$, and the Rashba coupling, $α\gg 1$, the low-energy physics is characterized by an almost flat single-particle dispersion. From an analytical approach for $α\to \infty$ and $N=2$, and from numerical exact diagonalization and Hartree-Fock calculations, we find a transition from a conventional unmagnetized ground state (for $λ<λ_c$) to an orbital ferromagnet (for $λ>λ_c$), with a large magnetization and a circulating charge current. We show that the critical interaction strength, $λ_c=λ_c(α,N)$, vanishes in the limit $α\to \infty$.