We derive an effective spin Hamiltonian for the one-dimensional half-filled tetramerized ionic-Hubbard model in the limit of strong on-site repulsion. We show that the effective Hamiltonian which describes the low-energy spin sector of the model is a spin S=1/2 Heisenberg Hamiltonian with alternating nearest-neighbour exchange.
We derive an effective spin Hamiltonian for the one-dimensional half-filled asymmetric ionic Hubbard model with alternating on-site interaction in the limit of strong repulsion. It is shown that the effective Hamiltonian is that of a spin $S=1/2$ anisotropic $XXZ$ Heisenberg chain with alternating next-nearest-neighbor and three-spin couplings in the presence of a uniform and a staggered magnetic field.
We investigate the local moment formation in the half-filled SU($N$) Hubbard model under a staggered ionic potential. As the Hubbard $U$ increases, the charge fluctuations are suppressed and eventually frozen when $U$ is above a critical value $U_c$, marking the development of well-defined local moment with integer $m$ fermions on the A-sublattice and $(N-m)$ fermions on the B-sublattice, respectively. We obtain an analytical solution for $U_c$ for the paramagnetic ground state within the variational Gutzwiller approximation and renormalized mean field theory. For large $N$, $U_c$ is found to …
We investigate the ionic Hubbard model (IHM) at half-filling in the limit of strong correlations and large ionic potential. The low energy effective Hamiltonian in this limit, obtained by a similarity transformation, is a modified $t-J$ model with effective second neighbour hopping terms. We explore the possibilities of d-wave pairing and extended s-wave pairing superconducting (SC) phases on a two dimensional square lattice at zero temperature within a Gutzwiller projected renormalized mean field theory. In the sector of solutions that forbid spin ordering, the system shows a finite non-zero …
We study the phase diagram of the ionic Hubbard model (IHM) at half-filling using dynamical mean field theory (DMFT), with two impurity solvers, namely, iterated perturbation theory (IPT) and continuous time quantum Monte Carlo (CTQMC). The physics of the IHM is governed by the competition between the staggered potential $Δ$ and the on-site Hubbard U. In both the methods we find that for a finite $Δ$ and at zero temperature, anti-ferromagnetic (AFM) order sets in beyond a threshold $U=U_{AF}$ via a first order phase transition below which the system is a paramagnetic band insulator. Both the m…
Ground state (GS) phase diagram of the one dimensional repulsive Hubbard model with both nearest neighbor ($t$) and next-nearest-neighbor ($t^{\prime}$) hopping and a staggered potential ($Δ$) is determined in the case of half-filled band and zero net magnetization within the mean-field theory. The model may be realized by cold atoms in engineered optical lattices. Connection between the peculiarities of the GS phase diagram of the interacting system and the topological Lifshitz transition in GS of free particle chain is discussed. The mean-field Hamiltonian is given by six order parameters, w…
A repulsive Hubbard model with both spin-asymmetric hopping (${t_\uparrow\neq t_\downarrow}$) and a staggered potential (of strength $Δ$) is studied in one dimension. The model is a compound of the mass-imbalanced (${t_\uparrow\neq t_\downarrow}$, ${Δ=0}$) and ionic (${t_\uparrow = t_\downarrow}$, ${Δ>0}$) Hubbard models, and may be realized by cold atoms in engineered optical lattices. We use mostly mean-field theory to determine the phases and phase transitions in the ground state for a half-filled band (one particle per site). We find that a period-two modulation of the particle (or charge)…
Charge Freezing in Zig-zag Chain Cuprates PrBa2Cu4O8 Observed by Cu Nuclear Quadrupole Resonance
本文报道了PrBa $_{2}$ Cu $_{4}$ O $_{8}$（一种具有近四分之一填充带的准一维导体）的链Cu位的核四极共振（NQR）研究.核自旋-晶格弛豫速率$1/T_{1}$在100 K附近出现一个明显的峰，这是由电场梯度（EFG）的涨落引起的.自旋回波衰减率$1/T_{2}$在50 K附近的不同温度下观察到类似的峰。这些结果和低温下NQR谱的加宽表明，电子或离子起源的缓慢电荷波动在低温下逐渐冻结。
Ground-state phase diagram of the one-dimensional Hubbard-model with an alternating potential
本文研究了一维半填充交替电势哈伯德模型的基态相图。我们利用基于精确对角化计算的能级交叉和唯象重正化群方法数值计算了该模型的全局相图。我们的结果支持Fabrizio，Gogolin和Nersesyan [Phys. Rev. Lett. 83，2014（1999）]：我们证实了作为中间态的自发二聚相的存在。此外，我们提供了数值证据来检查的临界相边界。特别地，我们对激发能隙进行了有限尺寸标度分析，以显示电荷部分的二维伊辛跃迁。另一方面，我们证实，二聚相的生存在强耦合的限制，这是电离性和相关效应之间的竞争的结果之一。
We demonstrate, using dynamical mean-field theory with the hybridization expansion continuous time quantum montecarlo impurity solver, a rich phase diagram with {\em correlation driven metallic and half-metallic phases} in a simple model of a correlated band insulator, namely, the half-filled ionic Hubbard model (IHM) with first {\em and} second neighbor hopping ($t$ and $t'$), an on-site repulsion $U$, and a staggered potential $Δ$. Without $t'$ the IHM has a direct transition from a paramagnetic band insulator (BI) to an antiferromagnetic Mott insulator (AFI) phase as $U$ increases. For weak…
