Interstitial-induced ferromagnetism in a two-dimensional Wigner crystal

Abstract

The two-dimensional Wigner crystal (WC) occurs in the strongly interacting regime ($r_s\gg 1$) of the two-dimensional electron gas (2DEG). The magnetism of a pure WC is determined by tunneling processes that induce multi-spin ring-exchange interactions, resulting in fully polarized ferromagnetism for large enough $r_s$. Recently, Hossain et al. [PNAS 117 (51) 32244-32250] reported the occurrence of a fully polarized ferromagnetic insulator at $r_s\gtrsim 35$ in an AlAs quantum well, but at temperatures orders of magnitude larger than the predicted exchange energies for the pure WC. Here, we analyze the large $r_s$ dynamics of an interstitial defect in the WC, and show that it produces local ferromagnetism with much higher energy scales. Three hopping processes are dominant, which favor a large, fully polarized ferromagnetic polaron. Based on the above results, we speculate concerning the phenomenology of the magnetism near the metal-insulator transition of the 2DEG.

4 pages + references & Supplementary (5 pages), 2+4 figures, 1 table. Minor revision based on comments

References in corpus (3)

• Phase Diagram of the Low-Density Two-Dimensional Homogeneous Electron Gas
• Observation of Spontaneous Ferromagnetism in a Two-Dimensional Electron System
• Discovery of an insulating ferromagnetic phase of electrons in two dimensions