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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-voltage 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.

Authors:
ORCiD logo; ; ORCiD logo; ORCiD logo; ; ; ;
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1730998
Grant/Contract Number:  
DEFG02-00-ER45841
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

Citation Formats

Hossain, M. S., Ma, M. K., Rosales, K. A. Villegas, Chung, Y. J., Pfeiffer, L. N., West, K. W., Baldwin, K. W., and Shayegan, M.. Observation of spontaneous ferromagnetism in a two-dimensional electron system. United States: N. p., 2020. Web. https://doi.org/10.1073/pnas.2018248117.
Hossain, M. S., Ma, M. K., Rosales, K. A. Villegas, Chung, Y. J., Pfeiffer, L. N., West, K. W., Baldwin, K. W., & Shayegan, M.. Observation of spontaneous ferromagnetism in a two-dimensional electron system. United States. https://doi.org/10.1073/pnas.2018248117
Hossain, M. S., Ma, M. K., Rosales, K. A. Villegas, Chung, Y. J., Pfeiffer, L. N., West, K. W., Baldwin, K. W., and Shayegan, M.. Thu . "Observation of spontaneous ferromagnetism in a two-dimensional electron system". United States. https://doi.org/10.1073/pnas.2018248117.
@article{osti_1730998,
title = {Observation of spontaneous ferromagnetism in a two-dimensional electron system},
author = {Hossain, M. S. and Ma, M. K. and Rosales, K. A. Villegas and Chung, Y. J. and Pfeiffer, L. N. and West, K. W. and Baldwin, K. W. and Shayegan, M.},
abstractNote = {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-voltage 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.},
doi = {10.1073/pnas.2018248117},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 51,
volume = 117,
place = {United States},
year = {2020},
month = {12}
}

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https://doi.org/10.1073/pnas.2018248117

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