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arXiv:cond-mat/9901343 · Physical review. B, Condensed matter

Hartree-Fock study of phase sensitivity in disordered rings

A. Kambili, Colin John Lambert, J. H. Jefferson

Published Sep 15, 1999• 26 citations
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Abstract

For a system of spinless fermions in a disordered mesoscopic ring, interactions can give rise to an enhancement of the persistent current by orders of magnitude. The increase in the current is associated with a charge reorganization of the ground state. The interaction strength for which this reorganization takes place is sample dependent and the logarithm averages over the ensemble are not representative. In this paper we demonstrate that the Hartree-Fock method closely reproduces results obtained by exact diagonalization. For spinless fermions subject to a short-range Coulomb repulsion U, we show that plots of phase sensitivity versus U exhibit sharp peaks associated with significant charge reorganization. Their positions are highly sample dependent and they disappear upon ensemble averaging. Having established that the Hartree-Fock method works well in one dimension, we present corresponding results for the phase sensitivity in two coupled chains.

DOI
10.1103/physrevb.60.7684

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For a system of spinless fermions in a disordered mesoscopic ring, interactions can give rise to an enhancement of the persistent current by orders of magnitude. The increase in the current is associated with a charge reorganization of the ground state. The interaction strength for which this reorganization takes place is sample dependent and the logarithm averages over the ensemble are not representative. In this paper we demonstrate that the Hartree-Fock method closely reproduces results obtained by exact diagonalization. For spinless fermions subject to a short-range Coulomb repulsion U, we show that plots of phase sensitivity versus U exhibit sharp peaks associated with significant charge reorganization. Their positions are highly sample dependent and they disappear upon ensemble averaging. Having established that the Hartree-Fock method works well in one dimension, we present corresponding results for the phase sensitivity in two coupled chains.
Persistent currents in disordered mesoscopic rings threaded by a magnetic flux are calculated using exact diagonalization methods in the one-dimensional (1D) case and self-consistent Hartree-Fock treatments for two dimensional (2D) systems. For multichannel systems, a comparative study between models of spinless or spinfull (Hubbard) fermions has been done. First, it is shown that a purely one-dimensional model can not reproduce the correct order of magnitude of the observed currents. For 2D systems, going beyond first order pertubative calculations, we show that the second harmonic of the current is {\it strongly suppressed} in the case of spinless fermion models but {\it significantly enhanced} for the Hubbard model. This reduction (resp. increase) of the second harmonic is related to a strong increase (resp. reduction) of the spacial charge density fluctuations. Our work underlines the important role of the spin degrees of freedom in the persistent currents.
Persistent currents flowing through disordered mesoscopic rings threaded by a magnetic flux are investigated. Models of fermions with on-site interactions (Hubbard model) or models of spinless fermions with nearest neighbor interactions are considered on 2D cylinders with twisted boundary conditions in one direction to account for a magnetic flux. Self-consistent Hartree-Fock methods are used to treat the electron-electron interaction beyond first order. We show that the second harmonic of the current (which is relevant in the diffusive regime) is strongly suppressed by the interaction in the case of spinless fermions while it is significantly enhanced in the Hubbard model. Our data also strongly suggest that the reduction (increase) of this harmonic is related to a strong increase (reduction) of the spatial fluctuations of the charge density.
Persistent currents in disordered multichannel mesoscopic rings threaded by a magnetic flux are calculated using exact diagonalizations and self-consistent Hartree-Fock treatments of two-dimensional tori and cylinders of spinless interacting fermions. The validity of the Hartree-Fock approximation is controlled by a direct comparison with the exact results on small 4\ifmmode\times\else\texttimes\fi{}4 clusters. The existence of a crossover value for the disorder parameter Wc{\mathit{W}}_{\mathit{c}}Wc​ (depending on the electronic density and the system size) separating two different regimes is established. Decomposing the current I(\ensuremath{\varphi}) in terms of its fundamental harmonics, we find that, while the first harmonic is always enhanced by the interaction, the second harmonic is enhanced for WWc{\mathit{W}}_{\mathit{c}}Wc​ and strongly suppressed otherwise. This effect is stronger as we increase the disorder.
Persistent currents flowing through disordered mesoscopic rings threaded by a magnetic flux are investigated. Models of fermions with on-site interactions (Hubbard model) or models of spinless fermions with nearest neighbor interactions are considered on 2D cylinders with twisted boundary conditions in one direction to account for a magnetic flux. Self-consistent Hartree-Fock methods are used to treat the electron-electron interaction beyond first order. We show that the second harmonic of the current (which is relevant in the diffusive regime) is {\it strongly suppressed} by the interaction in the case of spinless fermions while it is {\it significantly enhanced} in the Hubbard model. Our data also strongly suggest that the reduction (increase) of this harmonic is related to a strong increase (reduction) of the spacial fluctuations of the charge density.
In this paper, we investigate the ground state of two-dimensional disordered cylinders which contain spinless, interacting electrons using the Hartree-Fock approximation. Calculations of the deviation of the polarization from uniformity reveal a tendency of the charge to rearrange towards the ends of the system. The presence of disorder results in fluctuations of the deviation around its mean value, which are more pronounced when the disorder strength is of the order of the interaction between the electrons.
We present numerical results for the zero temperature persistent currents carried by interacting spinless electrons in disordered one-dimensional continuous rings. The disorder potential is described by a collection of δ-functions at random locations and strengths. The calculations are performed by a self-consistent Hartree–Fock (HF) approximation. Because the HF approximation retains the concept of single-electron levels, we compare the statistics of energy levels of noninteracting electrons with those of interacting electrons as well as of the level persistent currents. We find that the e–e interactions alter the levels and samples persistent currents and introduces a preffered diamagnetic current direction. In contrast to the analogous calculations that recently appeared in the literature for interacting spinless electrons in the presence of moderate disorder in tight-binding models we find no suppression of the persistent currents due to the e–e interactions.