Bloch ferromagnetism of composite fermions

Hossain, Md. Shafayat; Zhao, Tongzhou; Pu, Songyang; Mueed, M. A.; K., M.; Rosales, K. A. Villegas; Chung, Yoon Jang; Pfeiffer, L. N.; West, K. W.; Baldwin, K. W.; Jain, J. K.; Shayegan, M.

doi:10.1038/s41567-020-1000-z

Cited by 20 publications

(12 citation statements)

References 32 publications

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“…We consider a situation where the applied magnetic field B changes, to be consistent wit the experiment in Ref. [3], along with a change in density n according to a powerlaw specified manner: B ∼ n p , where p is a power law exponent. In the composite fermion experiment p = 1 [3], but we consider arbitrary p, asking how the ground state spin polarization of the interacting electron liquid changes as B, n both are varied together.…”

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confidence: 84%

“…Motivated by a recent experiment [3], where Bloch ferromagnetism has been reported in 2D composite fermions, we study theoretically the interplay between an applied magnetic field, coupled to electron spins causing the usual field-induced Zeeman spin splitting, and carrier density-induced exchange coupling leading to Bloch type spin-polarization in 2D electrons (We also provide results for the corresponding 3D case for completeness.). We consider a situation where the applied magnetic field B changes, to be consistent wit the experiment in Ref.…”

mentioning

confidence: 99%

“…[3], along with a change in density n according to a powerlaw specified manner: B ∼ n p , where p is a power law exponent. In the composite fermion experiment p = 1 [3], but we consider arbitrary p, asking how the ground state spin polarization of the interacting electron liquid changes as B, n both are varied together. In the experiment [3], B ∼ n was necessary simply to keep the 2D electron system maintain a fixed Landau level filling of half so that the composite fermions themselves, carrying two effective units of average flux quanta, can be thought of as being at zero magnetic field according to the wellknown Jain prescription [4,5].…”

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confidence: 99%

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Reentrant Bloch ferromagnetism

Sarma

2021

Phys. Rev. B

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An interacting electron liquid in two (2D) and three (3D) dimensions may undergo a paramagneticto-ferromagnetic quantum spin polarization transition at zero applied magnetic field, driven entirely by exchange interactions, as the system density (n) is decreased. This is known as Bloch ferromagnetism. We show theoretically that the application of an external magnetic field (B), which directly spin polarizes the system through Zeeman spin splitting, has an interesting effect on Bloch ferromagnetism if the applied field and carrier density are both decreased (from some initial applied high magnetic field at a high carrier density) in a power-law manner, B ∼ n p . For p < pc, with pc = 1(2/3) in 2(3)D, the system remains either fully spin-polarized or undergoes a single transition from a partially spin-polarized (with two Fermi surfaces corresponding to spin up and down electrons) to a fully spin-polarized state (with a single Fermi surface of one spin) as the density and field decrease, depending on whether the starting point is partially spin-polarized or fully spin-polarized. However, for p > pc, the system may undergo two transitions if starting from the fully spin-polarized state: first, a weak second order transition at high density and field from the field-induced fully polarized phase to the partially polarized phase; and then, at a lower field and density, a reentrant first order transition back to the fully spin-polarized phase again with a single Fermi surface.

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confidence: 84%

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confidence: 99%

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confidence: 99%

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Reentrant Bloch ferromagnetism

Sarma

2021

Phys. Rev. B

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“…Whether a Bloch-type strictly density-driven paramagnetic-toferromagnetic spin transition happens or not is still an open question, but any such transition can only occur at extreme low carrier densities which are inaccessible in any 3DEG systems. Recently, such a Bloch spin transition has been experimentally reported in 2D composite fermions at the half Landau level filling [2,3].…”

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confidence: 94%

“…1(b) and 1(c)], we set m = 0.2(1.1) in Eq. ( 1) for calculating the resistivity along the [100]([010]) direction, following the experimental paper [3]. Above the critical density the experimental resistivity is isotropic and thus we use the isotropic averaged density of states mass defined as m DOS = √ 0.2 × 1.1 = 0.46.…”

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confidence: 99%

Valley polarization transition in a two-dimensional electron gas

Ahn,

Sarma

2021

Preprint

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We theoretically study transport signatures associated with a spontaneous 2-valley to 1-valley quantum phase transition in a two-dimensional electron gas (2DEG) tuned by decreasing the 2D carrier density, as claimed in a recent experiment [Phys. Rev. Lett. 127, 116601 (2021)]. The key issue we focus on is whether the experimentally measured 2D resistivity as a function of carrier density is consistent (or not) with an underlying spontaneous valley-polarization transition as assumed uncritically in the experimental report. Our theoretical analysis is particularly germane since the experiment does not directly measure the change in the Fermi surface resulting from the valley polarization transition, but infers such a transition indirectly through transport measurements. We validate the experimental claim, showing that indeed the observed sudden change in the 2D resistivity is quantitatively consistent with a sudden change in the valley polarization from 2 to 1 at the critical density.

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