Observation of spontaneous ferromagnetism in a two-dimensional electron system

M. S. Hossain, M. K. Ma, K. A. Villegas Rosales, Y. J. Chung, L. N. Pfeiffer, K. W. West, K. W. Baldwin, M. Shayegan

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

What are the ground states of an interacting, low-density electron system? In the absence of disorder, it has long been expected that as the electron density is lowered, the exchange energy gained by aligning the electron spins should exceed the enhancement in the kinetic (Fermi) energy, leading to a (Bloch) ferromagnetic transition. At even lower densities, another transition to a (Wigner) solid, an ordered array of electrons, should occur. Experimental access to these regimes, however, has been limited because of the absence of a material platform that supports an electron system with very high quality (low disorder) and low density simultaneously. Here we explore the ground states of interacting electrons in an exceptionally clean, two-dimensional electron system confined to a modulation-doped AlAs quantum well. The large electron effective mass in this system allows us to reach very large values of the interaction parameter rs, defined as the ratio of the Coulomb to Fermi energies. As we lower the electron density via gate bias, we find a sequence of phases, qualitatively consistent with the above scenario: a paramagnetic phase at large densities, a spontaneous transition to a ferromagnetic state when rs surpasses 35, and then a phase with strongly nonlinear current-voltage characteristics, suggestive of a pinned Wigner solid, when rs exceeds '38. However, our sample makes a transition to an insulating state at rs '27, preceding the onset of the spontaneous ferromagnetism, implying that besides interaction, the role of disorder must also be taken into account in understanding the different phases of a realistic dilute electron system.

Original languageEnglish (US)
Pages (from-to)32244-32250
Number of pages7
JournalProceedings of the National Academy of Sciences of the United States of America
Volume117
Issue number51
DOIs
StatePublished - Dec 22 2020

All Science Journal Classification (ASJC) codes

  • General

Keywords

  • 2D electron system
  • Ferromagnetism
  • Magnetotransport
  • Metal-insulator transition
  • Wigner solid

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