AIP conference proceedings

Suppression of Spin Polarization in a Symmetric Electron-Electron Bilayer

Krishan Kumar, Rajinder Kumar Moudgil, Shailendra Kumar Tripathi, Keya Dharamvir, Ranjan Kumar, G. S. S. Saini

Published Jan 1, 2011• 0 citations

Abstract

We explore theoretically the feasibility of a spin‐polarized ground state in a symmetric electron‐electron bilayer by comparing the ground‐state energy in states of different spin polarization. Both the intra‐ and inter‐layer interactions are dealt within the framework of random‐phase approximation. We find that there occurs in the bilayer an abrupt paramagnetic‐ferromagnetic phase transition with the decreasing electron density irrespective of the magnitude of inter‐layer separation. Interestingly, the critical transition density is found to decrease with the diminishing layer spacing, implying therefore a suppression of spin polarization by interlayer interaction effects.

DOI: 10.1063/1.3653751

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AIP conference proceedings

Suppression of Spin Polarization in a Symmetric Electron-Electron Bilayer

Krishan Kumar, Rajinder Kumar Moudgil, Shailendra Kumar Tripathi, Keya Dharamvir, Ranjan Kumar, G. S. S. Saini

Published Jan 1, 2011• 0 citations

Publisher

Abstract

DOI: 10.1063/1.3653751

Related papers

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Quantum Monte Carlo study of a bilayer

U(2)\times U(2)

symmetric Hubbard model

SU(2)

spin rotational symmetry but preserves a

U(2)\times U(2)

invariance under mixing of same-spin electrons between layers. We show that despite the difference in symmetry, the bilayer model exhibits the same qualitative features found in the single-layer Hubbard model. These include stripe phases, whose nature is sensitive to the presence of next-nearest-neighbor hopping, a maximum in the Knight shift that moves to lower temperatures with increasing hole doping, and lack of evidence for intra-layer d-wave superconductivity. Instead, we find a superconducting phase, coexisting with stripes, whose critical temperature traces a dome as a function of doping and is due to inter-layer spin-polarized pairing that is induced by the ferromagnetic interaction.

SU(2)

spin rotational symmetry but preserves a $U(2)\ifmmode\times\else\texttimes\fi{}U(2)$ invariance under mixing of same-spin electrons between layers. We show that despite the difference in symmetry, the bilayer model exhibits the same qualitative features found in the single-layer Hubbard model. These include stripe phases, whose nature is sensitive to the presence of next-nearest-neighbor hopping, a maximum in the Knight shift that moves to lower temperatures with increasing hole doping, and lack of evidence for intralayer

d

-wave superconductivity. Instead, we find a superconducting phase, coexisting with stripes, whose critical temperature traces a dome as a function of doping and is due to interlayer spin-polarized pairing that is induced by the ferromagnetic interaction.

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, $B\ensuremath{\sim}{n}^{p}$. For

p<{p}_{c}

, with

{p}_{c}=1(2/3)

2(3)\mathrm{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>{p}_{c}

, 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.