Title: Observation of spontaneous ferromagnetism in a two-dimensional electron system

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 r_s, 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 r_s surpasses 35, and then a phase with strongly nonlinear current-voltagemore » characteristics, suggestive of a pinned Wigner solid, when r_s exceeds ≃38. However, our sample makes a transition to an insulating state at r_s≃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.« less

Authors:

Hossain, M. S.  ^[1];

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Ma, M. K. ^[1]; Rosales, K. A. Villegas  ^[1];

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Chung, Y. J.  ^[1];

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Pfeiffer, L. N. ^[1]; West, K. W. ^[1]; Baldwin, K. W. ^[1]; Shayegan, M. ^[1]

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+ Show Author Affiliations

1. Department of Electrical Engineering, Princeton University, Princeton, NJ 08544

Publication Date:

2020-12-03

Research Org.:

Princeton Univ., NJ (United States)

Sponsoring Org.:

USDOE Office of Science (SC)

OSTI Identifier:

1730998

Alternate Identifier(s):

OSTI ID: 1849360

Grant/Contract Number:  

DEFG02-00-ER45841; FG02-00ER45841

Resource Type:

Published Article

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Volume: 117 Journal Issue: 51; Journal ID: ISSN 0027-8424

Publisher:

Proceedings of the National Academy of Sciences

Country of Publication:

United States

Language:

English

Subject:

42 ENGINEERING; Science & Technology; 2D electron system; ferromagnetism; magnetotransport; metal–insulator transition; Wigner solid