Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:cond-mat/0510325 · Physical Review Letters

Creation and Destruction of a Spin Gap in Weakly Coupled Quarter-Filled Ladders

Bernhard Edegger, Hans Gerd Evertz, R. M. Noack

Published Apr 12, 2006• 7 citations
arXivHTMLPDF

Abstract

We investigate weakly coupled quarter-filled ladders with model parameters relevant for NaV(2)O(5) using density-matrix renormalization group calculations on an extended Hubbard model coupled to the lattice. NaV(2)O(5) exhibits super-antiferroelectric charge order with a zigzag pattern on each ladder. We show that this order causes a spin dimerization along the ladder and is accompanied by a spin gap of the same magnitude as that observed experimentally. The spin gap is destroyed again at large charge order due to a restructuring of the spins. An analysis of an effective spin model predicts a recreation of the gap by interladder singlets when the charge order increases further.

DOI
10.1103/physrevlett.96.146401

Related papers

Charge order induced by electron-lattice interaction in NaV2O5

Bernhard Edegger, Hans Gerd Evertz, R. M. Noack

We present density matrix renormalization group calculations of the ground-state properties of quarter-filled ladders including static electron-lattice coupling. Isolated ladders and two coupled ladders are considered, with model parameters obtained from band-structure calculations for ${\ensuremath{\alpha}}^{\ensuremath{'}}\text{\ensuremath{-}}\mathrm{Na}{\mathrm{V}}_{2}{\mathrm{O}}_{5}$. The relevant Holstein coupling to the lattice causes static out-of-plane lattice distortions, which appear concurrently with a charge-ordered state and which exhibit the same zigzag pattern observed in experiments. The inclusion of electron-lattice coupling drastically reduces the critical nearest-neighbor Coulomb repulsion ${V}_{c}$ needed to obtain the charge-ordered state. No spin gap is present in the ordered phase. The charge ordering is driven by the Coulomb repulsion and the electron-lattice interaction. With electron-lattice interaction, coupling two ladders has virtually no effect on ${V}_{c}$ or on the characteristics of the charge-ordered phase. At $V=0.46\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, a value consistent with previous estimates, the lattice distortion, charge gap, charge-order parameter, and the effective spin coupling are in good agreement with experimental data for $\mathrm{Na}{\mathrm{V}}_{2}{\mathrm{O}}_{5}$.

arXiv:cond-mat/0505685•Physical Review B•Aug 24, 2005•5 citations

Phase diagram of the quarter-filled extended Hubbard model on a two-leg ladder

Matthias Vojta C, A. Hübsch, R. M. Noack

We investigate the ground-state phase diagram of the quarter-filled Hubbard ladder with nearest-neighbor Coulomb repulsion $V$ using the density matrix renormalization-group technique. The ground state is homogeneous at small $V,$ a ``checkerboard'' charge-ordered insulator at large $V$ and not too small on site Coulomb repulsion U, and is phase separated for moderate or large $V$ and small U. The zero-temperature transition between the homogeneous and the charge-ordered phase is found to be second order. In both the homogeneous and the charge-ordered phases the existence of a spin gap mainly depends on the ratio of interchain to intrachain hopping. In the second part of the paper we construct an effective Hamiltonian for the spin degrees of freedom in the strong-coupling, charge-ordered regime that maps the system onto a frustrated spin chain. The opening of a spin gap is thus connected with spontaneous dimerization.

arXiv:cond-mat/0008068•Physical review. B, Condensed matter•Jan 8, 2001•51 citations

Separated Spin and Charge Excitations and their Coupling in the Spin-Pseudospin Model for Quarter-Filled Ladders

Y. Ohta, T. Nakaegawa, Satoshi Ejima

Quantum Monte Carlo (QMC) and density-matrix renormalization group (DMRG) methods are used to study the coupled spin-pseudospin Hamiltonian in one-dimension (1D) that models the charge-ordering instability of the anisotropic Hubbard ladder at quarter filling. We calculate the temperature dependence of the uniform spin susceptibility and specific heat as well as the spin and charge excitation spectra of the system. We show that there is a parameter and temperature region where the spin degrees of freedom are separated from the charge degrees of freedom and behave like a 1D antiferromagnetic Heisenberg model, and that, outside this parameter region and above a crossover temperature, the spin excitations are largely affected by the charge fluctuation. We argue that observed anomalous spin dynamics in the disorder phase of a typical charge-ordered material $α'$-NaV$_2$O$_5$ may possibly be a consequence of this type of spin-charge coupling.

arXiv:cond-mat/0309433•Sep 18, 2003•0 citations

Spin and charge excitations in the anisotropic Hubbard ladder at quarter filling with charge-ordering instability

Y. Ohta, T. Nakaegawa, Satoshi Ejima

Quantum Monte Carlo and density-matrix renormalization group methods are used to study the coupled spin-pseudospin Hamiltonian in one-dimension (1D) that models the charge-ordering instability of the anisotropic Hubbard ladder at quarter filling. We calculate the temperature dependence of the uniform spin susceptibility and specific heat as well as the spin and charge excitation spectra of the system. We thereby show that there is a parameter and temperature region where the spin degrees of freedom are separated from the charge degrees of freedom and behave like a 1D antiferromagnetic Heisenberg model, and that, outside this parameter region and above a crossover temperature, the spin excitations are largely affected by the charge fluctuations. We argue that observed anomalous spin dynamics in the disorder phase of a typical charge-ordered material ${\ensuremath{\alpha}}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{NaV}}_{2}{\mathrm{O}}_{5}$ may possibly be a consequence of this type of spin-charge coupling.

arXiv:cond-mat/0512310•Physical Review B•Jan 3, 2006•5 citations

Tomonaga-Luttinger parameters and spin excitations in the dimerized extended Hubbard model

Satoshi Ejima, Florian Gebhard, Satoshi Nishimoto

We study the one-dimensional extended Hubbard model with alternating size of the hopping integrals using the density-matrix renormalization group method. We calculate the spin gap, the Tomonaga-Luttinger parameter, and the charge-density-wave order parameter for various dimerizations, interaction strengths, and band fillings. At half band-filling the spin and charge excitations are gapped but these gaps disappear for infinitesimal hole doping. At quarter filling, the umklapp scattering in the half-filled lower Peierls band generates a gap for the charge excitations but the gapless spin excitations can be described in terms of an effective antiferromagnetic Heisenberg model. Beyond a critical strength for the nearest-neighbor interaction, the dimerized extended Hubbard model at quarter filling develops a charge-density-wave ground state. The dimerization and the nearest-neighbor Coulomb interaction strongly reduce the Tomonaga-Luttinger parameter from its value for the bare Hubbard model. We discuss the relevance of our findings for the Bechgaard salts.

arXiv:cond-mat/0605433•Physical Review B•Dec 14, 2006•21 citations

Charge ordering in quasi-one-dimensional systems with frustrating interactions

Siddhartha Lal, M. S. Laad

Motivated by the co-existing charge and spin order found in strongly correlated ladder systems, we study an effective pseudospin model on a coupled two-leg ladder. A bosonisation analysis yields a rich phase diagram showing Wigner/Peierls charge order and Neel/dimer spin order. In a broad parameter regime, the orbital antiferromagnetic phase is found to be stable. An intermediate gapless phase of finite width is found to lie in between two charge-ordered gapped phases. Our work is potentially relevant for a unified description of a class of strongly correlated, quarter-filled ladder systems.

arXiv:cond-mat/0511458•Nov 18, 2005•0 citations
We investigate weakly coupled quarter-filled ladders with model parameters relevant for NaV(2)O(5) using density-matrix renormalization group calculations on an extended Hubbard model coupled to the lattice. NaV(2)O(5) exhibits super-antiferroelectric charge order with a zigzag pattern on each ladder. We show that this order causes a spin dimerization along the ladder and is accompanied by a spin gap of the same magnitude as that observed experimentally. The spin gap is destroyed again at large charge order due to a restructuring of the spins. An analysis of an effective spin model predicts a recreation of the gap by interladder singlets when the charge order increases further.
We present density matrix renormalization group calculations of the ground-state properties of quarter-filled ladders including static electron-lattice coupling. Isolated ladders and two coupled ladders are considered, with model parameters obtained from band-structure calculations for ${\ensuremath{\alpha}}^{\ensuremath{'}}\text{\ensuremath{-}}\mathrm{Na}{\mathrm{V}}_{2}{\mathrm{O}}_{5}$. The relevant Holstein coupling to the lattice causes static out-of-plane lattice distortions, which appear concurrently with a charge-ordered state and which exhibit the same zigzag pattern observed in experiments. The inclusion of electron-lattice coupling drastically reduces the critical nearest-neighbor Coulomb repulsion Vc{V}_{c}Vc​ needed to obtain the charge-ordered state. No spin gap is present in the ordered phase. The charge ordering is driven by the Coulomb repulsion and the electron-lattice interaction. With electron-lattice interaction, coupling two ladders has virtually no effect on Vc{V}_{c}Vc​ or on the characteristics of the charge-ordered phase. At V=0.46eVV=0.46\phantom{\rule{0.3em}{0ex}}\mathrm{eV}V=0.46eV, a value consistent with previous estimates, the lattice distortion, charge gap, charge-order parameter, and the effective spin coupling are in good agreement with experimental data for NaV2O5\mathrm{Na}{\mathrm{V}}_{2}{\mathrm{O}}_{5}NaV2​O5​.
We investigate the ground-state phase diagram of the quarter-filled Hubbard ladder with nearest-neighbor Coulomb repulsion VVV using the density matrix renormalization-group technique. The ground state is homogeneous at small V,V,V, a ``checkerboard'' charge-ordered insulator at large VVV and not too small on site Coulomb repulsion U, and is phase separated for moderate or large VVV and small U. The zero-temperature transition between the homogeneous and the charge-ordered phase is found to be second order. In both the homogeneous and the charge-ordered phases the existence of a spin gap mainly depends on the ratio of interchain to intrachain hopping. In the second part of the paper we construct an effective Hamiltonian for the spin degrees of freedom in the strong-coupling, charge-ordered regime that maps the system onto a frustrated spin chain. The opening of a spin gap is thus connected with spontaneous dimerization.
Quantum Monte Carlo (QMC) and density-matrix renormalization group (DMRG) methods are used to study the coupled spin-pseudospin Hamiltonian in one-dimension (1D) that models the charge-ordering instability of the anisotropic Hubbard ladder at quarter filling. We calculate the temperature dependence of the uniform spin susceptibility and specific heat as well as the spin and charge excitation spectra of the system. We show that there is a parameter and temperature region where the spin degrees of freedom are separated from the charge degrees of freedom and behave like a 1D antiferromagnetic Heisenberg model, and that, outside this parameter region and above a crossover temperature, the spin excitations are largely affected by the charge fluctuation. We argue that observed anomalous spin dynamics in the disorder phase of a typical charge-ordered material α′α'α′-NaV2_22​O5_55​ may possibly be a consequence of this type of spin-charge coupling.
Quantum Monte Carlo and density-matrix renormalization group methods are used to study the coupled spin-pseudospin Hamiltonian in one-dimension (1D) that models the charge-ordering instability of the anisotropic Hubbard ladder at quarter filling. We calculate the temperature dependence of the uniform spin susceptibility and specific heat as well as the spin and charge excitation spectra of the system. We thereby show that there is a parameter and temperature region where the spin degrees of freedom are separated from the charge degrees of freedom and behave like a 1D antiferromagnetic Heisenberg model, and that, outside this parameter region and above a crossover temperature, the spin excitations are largely affected by the charge fluctuations. We argue that observed anomalous spin dynamics in the disorder phase of a typical charge-ordered material ${\ensuremath{\alpha}}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{NaV}}_{2}{\mathrm{O}}_{5}$ may possibly be a consequence of this type of spin-charge coupling.
We study the one-dimensional extended Hubbard model with alternating size of the hopping integrals using the density-matrix renormalization group method. We calculate the spin gap, the Tomonaga-Luttinger parameter, and the charge-density-wave order parameter for various dimerizations, interaction strengths, and band fillings. At half band-filling the spin and charge excitations are gapped but these gaps disappear for infinitesimal hole doping. At quarter filling, the umklapp scattering in the half-filled lower Peierls band generates a gap for the charge excitations but the gapless spin excitations can be described in terms of an effective antiferromagnetic Heisenberg model. Beyond a critical strength for the nearest-neighbor interaction, the dimerized extended Hubbard model at quarter filling develops a charge-density-wave ground state. The dimerization and the nearest-neighbor Coulomb interaction strongly reduce the Tomonaga-Luttinger parameter from its value for the bare Hubbard model. We discuss the relevance of our findings for the Bechgaard salts.
Motivated by the co-existing charge and spin order found in strongly correlated ladder systems, we study an effective pseudospin model on a coupled two-leg ladder. A bosonisation analysis yields a rich phase diagram showing Wigner/Peierls charge order and Neel/dimer spin order. In a broad parameter regime, the orbital antiferromagnetic phase is found to be stable. An intermediate gapless phase of finite width is found to lie in between two charge-ordered gapped phases. Our work is potentially relevant for a unified description of a class of strongly correlated, quarter-filled ladder systems.