arXiv:cond-mat/0109467 · Physical review. B, Condensed matter

Charge-density waves in one-dimensional Hubbard superlattices

Thereza Paiva, Raimundo R. dos Santos

Published Mar 27, 2002• 19 citations

Abstract

We study the formation of charge density waves (CDW's) in one-dimensional Hubbard superlattices, modeled by a repeated pattern of repulsive $(U>0)$ and free $(U=0)$ sites. By means of Lanczos diagonalizations for the ground state, we calculate the charge structure factor. Our results show that while the superlattice structure affects the modulation of the charge density waves, the periodicity can still be predicted through an effective density. We also show that, for a fixed repulsive layer thickness, the periodicity of the CDW is an oscillatory function of the free layer thickness.

DOI: 10.1103/physrevb.65.153101

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arXiv:cond-mat/0109467 · Physical review. B, Condensed matter

Charge-density waves in one-dimensional Hubbard superlattices

Thereza Paiva, Raimundo R. dos Santos

Published Mar 27, 2002• 19 citations

arXiv HTML PDF

Abstract

We study the formation of charge density waves (CDW's) in one-dimensional Hubbard superlattices, modeled by a repeated pattern of repulsive

(U>0)

and free

(U=0)

sites. By means of Lanczos diagonalizations for the ground state, we calculate the charge structure factor. Our results show that while the superlattice structure affects the modulation of the charge density waves, the periodicity can still be predicted through an effective density. We also show that, for a fixed repulsive layer thickness, the periodicity of the CDW is an oscillatory function of the free layer thickness.

DOI: 10.1103/physrevb.65.153101

Related papers

Modulation of charge-density waves by superlattice structures

André Luiz Malvezzi, Thereza Paiva, Raimundo R. dos Santos

We discuss the interplay between electronic correlations and an underlying superlattice structure in determining the period of charge density waves (CDW's), by considering a one-dimensional Hubbard model with a repeated (nonrandom) pattern of repulsive $(U>0)$ and free $(U=0)$ sites. Density matrix renormalization group diagonalization of finite systems (up to 120 sites) is used to calculate the charge-density correlation function and structure factor in the ground state. The modulation period can still be predicted through effective Fermi wave vectors ${k}_{F}^{*}$ and densities, and we have found that it is much more sensitive to electron (or hole) doping, both because of the narrow range of densities needed to go from ${q}^{*}=0$ to $\ensuremath{\pi}$, but also due to sharp $2{k}_{F}^{*}\ensuremath{-}4{k}_{F}^{*}$ transitions; these features render CDW's more versatile for actual applications in heterostructures than in homogeneous systems.We discuss the interplay between electronic correlations and an underlying superlattice structure in determining the period of charge density waves (CDW's), by considering a one-dimensional Hubbard model with a repeated (nonrandom) pattern of repulsive $(U>0)$ and free $(U=0)$ sites. Density matrix renormalization group diagonalization of finite systems (up to 120 sites) is used to calculate the charge-density correlation function and structure factor in the ground state. The modulation period can still be predicted through effective Fermi wave vectors ${k}_{F}^{*}$ and densities, and we have found that it is much more sensitive to electron (or hole) doping, both because of the narrow range of densities needed to go from ${q}^{*}=0$ to $\ensuremath{\pi}$, but also due to sharp $2{k}_{F}^{*}\ensuremath{-}4{k}_{F}^{*}$ transitions; these features render CDW's more versatile for actual applications in heterostructures than in homogeneous systems.

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The charge structure factor of the half-filled Hubbard superlattices with one on-site repulsive site and [Formula: see text] free sites per unit cell is investigated numerically. The behaviors of charge structure reveal a kind of even–odd [Formula: see text] disparity. For even [Formula: see text], we always observe a commensurate charge density wave (CDW). For odd [Formula: see text], we observe a commensurate–incommensurate CDW transition at a critical on-site repulsion around the particle–hole symmetric point. This transition results from the competition between the local charge correlations with odd distance and even distance.The charge structure factor of the half-filled Hubbard superlattices with one on-site repulsive site and [Formula: see text] free sites per unit cell is investigated numerically. The behaviors of charge structure reveal a kind of even–odd [Formula: see text] disparity. For even [Formula: see text], we always observe a commensurate charge density wave (CDW). For odd [Formula: see text], we observe a commensurate–incommensurate CDW transition at a critical on-site repulsion around the particle–hole symmetric point. This transition results from the competition between the local charge correlations with odd distance and even distance.

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Multiperiodic magnetic structures in Hubbard superlattices

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We consider fermions in one-dimensional superlattices (SL's), modeled by site-dependent Hubbard- $U$ couplings arranged in a repeated pattern of repulsive (i.e., $U>0)$ and free $(U=0)$ sites. Density matrix renormalization group diagonalization of finite systems is used to calculate the local moment and the magnetic structure factor in the ground state. We have found four regimes for magnetic behavior: uniform local moments forming a spin-density wave (SDW), ``floppy'' local moments with short-ranged correlations, local moments on repulsive sites forming long-period SDW's superimposed with short-ranged correlations, and local moments on repulsive sites solely with long-period SDW's; the boundaries between these regimes depend on the range of electronic densities $\ensuremath{\rho}$ and on the SL aspect ratio. Above a critical electronic density, ${\ensuremath{\rho}}_{\ensuremath{\uparrow}\ensuremath{\downarrow}},$ the SDW period oscillates both with $\ensuremath{\rho}$ and with the spacer thickness. The former oscillation allows one to reproduce all SDW wave vectors within a small range of electronic densities, unlike the homogeneous system. The latter oscillation is related to the exchange oscillation observed in magnetic multilayers. A crossover between regimes of ``thin'' to ``thick'' layers has also been observed.We consider fermions in one-dimensional superlattices (SL's), modeled by site-dependent Hubbard-$U$ couplings arranged in a repeated pattern of repulsive (i.e., $U>0)$ and free $(U=0)$ sites. Density matrix renormalization group diagonalization of finite systems is used to calculate the local moment and the magnetic structure factor in the ground state. We have found four regimes for magnetic behavior: uniform local moments forming a spin-density wave (SDW), ``floppy'' local moments with short-ranged correlations, local moments on repulsive sites forming long-period SDW's superimposed with short-ranged correlations, and local moments on repulsive sites solely with long-period SDW's; the boundaries between these regimes depend on the range of electronic densities $\ensuremath{\rho}$ and on the SL aspect ratio. Above a critical electronic density, ${\ensuremath{\rho}}_{\ensuremath{\uparrow}\ensuremath{\downarrow}},$ the SDW period oscillates both with $\ensuremath{\rho}$ and with the spacer thickness. The former oscillation allows one to reproduce all SDW wave vectors within a small range of electronic densities, unlike the homogeneous system. The latter oscillation is related to the exchange oscillation observed in magnetic multilayers. A crossover between regimes of ``thin'' to ``thick'' layers has also been observed.

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Thereza Paiva, Raimundo R. dos Santos

We study the metal-insulator transition in one-dimensional Hubbard superlattices, modeled by a repeated pattern of repulsive (i.e., positive on-site coupling) and free sites. The evolution of the local moment and of the charge gap (calculated from Lanczos diagonalization of chains up to 18 sites), together with a strong-coupling analysis, show that the electron density at which the system is insulating increases with the size of the free layer, relative to the repulsive one. In the insulating state, the mechanism of interaction between fermions separated by a free layer is the analog of superexchange, and the charge gap display universal features.We study the metal-insulator transition in one-dimensional Hubbard superlattices, modeled by a repeated pattern of repulsive (i.e., positive on-site coupling) and free sites. The evolution of the local moment and of the charge gap (calculated from Lanczos diagonalization of chains up to 18 sites), together with a strong-coupling analysis, show that the electron density at which the system is insulating increases with the size of the free layer, relative to the repulsive one. In the insulating state, the mechanism of interaction between fermions separated by a free layer is the analog of superexchange, and the charge gap display universal features.

arXiv:cond-mat/9807302Physical review. B, Condensed matterOct 15, 199830 citations

Electronic Correlations in One-Dimensional Superlattices

Thereza Paiva, Raimundo R. dos Santos

We consider fermions on a one-dimensional superlattice, represented by a repeated pattern of repulsive (i.e., positive Hubbard $U$ ) and free (i.e., $U\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$ ) sites. Lanczos diagonalization of chains up to 12 sites at half filling shows that some patterns give rise to a weak form of frustration, sufficient to wipe out the spin-density-wave (SDW) correlations present in the otherwise homogeneous system. On the other hand, SDW correlations appear for some patterns above half filling, a feature absent in the homogeneous case. Below half filling, the local-moment maxima are displaced from the repulsive to the free sites. The peak in the magnetic structure factor is also shifted from $q\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{\pi}$, for the alternating configuration when $\ensuremath{\rho}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/3$ and 5/3.We consider fermions on a one-dimensional superlattice, represented by a repeated pattern of repulsive (i.e., positive Hubbard $U$) and free (i.e., $U\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$) sites. Lanczos diagonalization of chains up to 12 sites at half filling shows that some patterns give rise to a weak form of frustration, sufficient to wipe out the spin-density-wave (SDW) correlations present in the otherwise homogeneous system. On the other hand, SDW correlations appear for some patterns above half filling, a feature absent in the homogeneous case. Below half filling, the local-moment maxima are displaced from the repulsive to the free sites. The peak in the magnetic structure factor is also shifted from $q\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{\pi}$, for the alternating configuration when $\ensuremath{\rho}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/3$ and 5/3.

Physical Review LettersFeb 12, 199631 citations

Effect of external electric field on the charge density waves in one-dimensional Hubbard superlattices

Jayeeta Chowdhury, S N Karmakar, Bibhas Bhattacharyya

We have studied the ground state of one-dimensional Hubbard superlattice structures with different unit-cell sizes in the presence of an electric field. A self-consistent Hartree-Fock approximation calculation is done in the weak- to intermediate-interaction regime. Studying the charge gap at the Fermi level and the charge density structure factor, we get an idea of how the charge modulation on the superlattice is governed by the competition between the electronic correlation and the external electric field.We have studied the ground state of one-dimensional Hubbard superlattice structures with different unit-cell sizes in the presence of an electric field. A self-consistent Hartree-Fock approximation calculation is done in the weak- to intermediate-interaction regime. Studying the charge gap at the Fermi level and the charge density structure factor, we get an idea of how the charge modulation on the superlattice is governed by the competition between the electronic correlation and the external electric field.

arXiv:0810.5624Journal of Physics Condensed MatterDec 1, 20083 citations

We study the formation of charge density waves (CDW's) in one-dimensional Hubbard superlattices, modeled by a repeated pattern of repulsive

(U>0)

and free

(U=0)

(U>0)

and free

(U=0)

sites. Density matrix renormalization group diagonalization of finite systems (up to 120 sites) is used to calculate the charge-density correlation function and structure factor in the ground state. The modulation period can still be predicted through effective Fermi wave vectors

{k}_{F}^{*}

and densities, and we have found that it is much more sensitive to electron (or hole) doping, both because of the narrow range of densities needed to go from

{q}^{*}=0

to $\ensuremath{\pi}$, but also due to sharp $2{k}_{F}^{*}\ensuremath{-}4{k}_{F}^{*}$ transitions; these features render CDW's more versatile for actual applications in heterostructures than in homogeneous systems.

We consider fermions in one-dimensional superlattices (SL's), modeled by site-dependent Hubbard-

U

couplings arranged in a repeated pattern of repulsive (i.e.,

U>0)

and free

(U=0)

sites. Density matrix renormalization group diagonalization of finite systems is used to calculate the local moment and the magnetic structure factor in the ground state. We have found four regimes for magnetic behavior: uniform local moments forming a spin-density wave (SDW), ``floppy'' local moments with short-ranged correlations, local moments on repulsive sites forming long-period SDW's superimposed with short-ranged correlations, and local moments on repulsive sites solely with long-period SDW's; the boundaries between these regimes depend on the range of electronic densities $\ensuremath{\rho}$ and on the SL aspect ratio. Above a critical electronic density, ${\ensuremath{\rho}}_{\ensuremath{\uparrow}\ensuremath{\downarrow}},$ the SDW period oscillates both with $\ensuremath{\rho}$ and with the spacer thickness. The former oscillation allows one to reproduce all SDW wave vectors within a small range of electronic densities, unlike the homogeneous system. The latter oscillation is related to the exchange oscillation observed in magnetic multilayers. A crossover between regimes of ``thin'' to ``thick'' layers has also been observed.

We consider fermions on a one-dimensional superlattice, represented by a repeated pattern of repulsive (i.e., positive Hubbard

U

) and free (i.e.,

U\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0

) sites. Lanczos diagonalization of chains up to 12 sites at half filling shows that some patterns give rise to a weak form of frustration, sufficient to wipe out the spin-density-wave (SDW) correlations present in the otherwise homogeneous system. On the other hand, SDW correlations appear for some patterns above half filling, a feature absent in the homogeneous case. Below half filling, the local-moment maxima are displaced from the repulsive to the free sites. The peak in the magnetic structure factor is also shifted from $q\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{\pi}$, for the alternating configuration when $\ensuremath{\rho}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/3$ and 5/3.