共查询到19条相似文献,搜索用时 187 毫秒
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应用密度矩阵重整化群方法, 研究了存在交错离子势Δ时一维半满扩展Hubbard模型的相图. 通过计算关联函数、结构因子、位置算符等方法, 描绘了从Mott绝缘体-键有序绝缘体-Band 绝缘体的特性并给出了精确的相边界. 研究发现: 中间的键有序绝缘体相在相图中占据了很小的一部分区域, 当存在离子势Δ的情况下, 这个区域将会有所增大; 而当相互作用足够强时, 这个中间相消失. 给出了离子Hubbard模型(最近邻电子-电子相互作用V=0)的相图. 相似文献
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通过综合模式搜索法、广义Lagrange乘子法、以及转轴法等多种数值方法, 建立了一套针对多轨道Hubbard模型隶玻色子解法的数值优化方法. 该数值方法能够在考虑晶场劈裂、轨道间跳跃以及真实能带结构基础上, 利用隶玻色子方法计算实际关联电子材料的性质. 首先利用该方法计算了两轨道体系的Mott金属-绝缘体转变性质, 得到了与目前已有工作一致的结果; 然后利用该方法讨论了Coulomb关联对三轨道体系NaxCoO2的影响. 结果表明: 在中间关联情况下由eg'轨道形成的六个小Fermi面消失, 原因是由于电子关联导致该轨道上的空穴数随U减少. 这些结果也证实了算法的正确性和有效性.
关键词:
多轨道Hubbard模型
隶玻色子
Mott转变
xCoO2')" href="#">NaxCoO2 相似文献
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耦合双量子点中电子间静电相互作用对电子在系统中隧穿效应具有重要影响.考虑电子隧穿,交换及Hubbard关联作用后,在单态近似下,本文求解了耦合双量子点二电子问题,讨论了铁磁基态及Mott局域化态出现的条件。这里的结果表明电子的隧穿不利于铁磁基态的形成,Hubbard关联越强越有利于Mott局域化态的形成,并且在交换作用下Mott局域化态会转变为铁磁基态. 此外,外场可以诱导磁序相的改变。 相似文献
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各种电致发光聚合物具有非简并基态.当电子和空穴注入后,形成的载流子是极化子.极化子的大小和能量决定于电子相互作用.目前大家采用Hubbard model来描述聚合物中的电子相互作用,所得到的结果与实验不符.Hubbard model和extended Hubbard model对窄能带体系是好的近似,但聚合物是宽能带,反映价键关联的非对角相互作用(在extended Hubbard model中被略去)有重要贡献,特别是在强屏蔽情况下,价键关联与Hubbard关联相互竞争,可纠正现有理论的缺陷.
关键词: 相似文献
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基于第一性原理全势线性缀加平面波方法和局域密度近似(LDA),对ReSi1.75的基态晶格属性进行了研究. 结构优化的结果表明,ReSi1.75的基态平衡晶格常数比实验值小约0.6%. 在LDA计算基础上,考虑局域的Re的d电子库仑作用,用LDA+U方法计算了ReSi1.75的电子结构,发现当Ueff=U-J=4.4eV时,能带结构呈半导体性质. 具有0.12eV
关键词:
1.75')" href="#">ReSi1.75
局域密度近似
自相互修正作用
电子结构 相似文献
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本文采用第一性原理的方法系统研究了UO2的晶体结构、电子结构和弹性性质. 在计算中采用广义梯度近似结合Hubbard U项描述电子的局域强关联效应. 首先通过计算能带带隙大小并与理论值比较的方法, 得到了合理的有效库仑相关作用能(Ueff)的取值, 同时通过态密度的计算, 进一步验证了Ueff取值的合理性. 计算得到UO2中U原子的Ueff值为3.30 eV (Ueff=U-J, U=3.70 eV, J=0.40 eV). 应用此参数计算得到的UO2晶格常数为5.54 Å, 带隙宽度为2.17 eV. 该结果优于目前现有的研究结果, 同时在同样的Ueff值条件下计算所得到的弹性常数与实验值也符合得较好. 相较于之前的基于实验测量并分析得到的Ueff值, 我们所采用的方法在对UO2性质描述上更为准确. 不同的有效库仑相关作用能取值下的态密度结果表明, 有效库仑相关作用能的大小可以影响铀原子5f电子轨道的分布. 相似文献
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We solve the attractive Hubbard model for arbitrary interaction strengths within dynamical mean-field theory. We compute the transition temperature for superconductivity and analyze electron pairing in the normal phase. The normal state is a Fermi liquid at weak coupling and a non-Fermi-liquid state with a spin gap at strong coupling. Away from half filling, the quasiparticle weight vanishes discontinuously at the transition between the two normal states. 相似文献
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The ground state phase diagram of the weakly coupled extended Hubbard model with intraatomic attraction has been derived with the Hartree theory formulated in terms of the Bogoliubov variational approach. For a given value of electron density, the nature of the ordered ground state depends essentially on the sign and the strength of the nearest neighbor coupling. Some features are similar to those in the strong coupling limit obtained earlier. 相似文献
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We study the interplay between the spin-liquid and Kondo physics, as related to the nonmagnetic part of the phase diagram of heavy fermion materials. Within the unrestricted mean-field treatment of the infinite-U 2D Anderson-Heisenberg model, we find that there are two topologically distinct nondegenerate uniform heavy Fermi liquid states that may form as a consequence of the Kondo coupling between spinons and conduction electrons. For certain carrier concentrations, the uniform Fermi liquid becomes unstable with respect to the formation of a new kind of anharmonic "Kondo stripe" state with inhomogeneous Kondo screening strength and the charge density modulation. These features are experimentally measurable and thus may help to establish the relevance of the spin-liquid correlations to heavy fermion materials. 相似文献
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洪德耦合相互作用是导致多轨道体系发生轨道选择Mott相变的重要因素之一. 通过调控洪德耦合相互作用来研究其不同组成部分对轨道选择Mott相变的作用. 利用基于Lanczos 求解器的动力学平均场理论, 对比了双轨道的J模型和Jz模型的金属-绝缘体相变, 并重点讨论洪德耦合中的自旋翻转项和电子对跃迁项以及轨道宽度比值W2/W1如何影响轨道选择Mott 相变. 在J模型的相图中, Mott选择相占有较大的区域, 而Jz模型的轨道选择Mott 相只存在于一个很狭窄的区域内, 这说明自旋翻转项及电子对跳跃项是有利于轨道选择Mott相变发生的关键因素. 此外当轨道宽度之比大于W2/W1=0.7时, Jz 模型的轨道选择Mott 相会完全消失, 而J模型中只要轨道宽度不同都存在轨道选择Mott相. 因而, 简化后的Jz 模型只是在特定条件下才适合于研究轨道选择Mott相变. 相似文献
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Compact quantum electrodynamics in 2 + 1 dimensions often arises as an effective theory for a Mott insulator, with the Dirac fermions representing the low-energy spinons. An important and controversial issue in this context is whether a deconfinement transition takes place. We perform a renormalization group analysis to show that deconfinement occurs when N > Nc = 36/pi3 approximately to 1.161, where N is the number of fermion replica. For N < Nc, however, there are two stable fixed points separated by a line containing a unstable nontrivial fixed point: a fixed point corresponding to the scaling limit of the noncompact theory, and another one governing the scaling behavior of the compact theory. The string tension associated with the confining interspinon potential is shown to exhibit a universal jump as N --> Nc-. Our results imply the stability of a spin liquid at the physical value N = 2 for Mott insulators. 相似文献
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LIN Ji GAO Xian-Long WANG Ke-Lin 《理论物理通讯》2007,47(1):161-166
We present a comparative study of the ground state of the one-dimensional Hubbard model. We first use a new fermion coherent state method in the framework of Fermi liquid theory by introducing a hole operator and considering the interactions of two pairs electrons and holes. We construct the ground state of the Hubbard model as |〉=[f+∑^tφk1σ1hk2σ2ck3σ3hk4σ4 ∏exp(ρck1σ1 hk2σ2)]|〉0,where φ and ρ are the coupling constants. Our results are then compared to those of varlational methods, density functional theory based on the exact solvable Bethe ansatz solutions, variational Monto-Carlo method (VMC) as well as to the exact result of the infinite system. We find satisfactory agreement between the fermion coherent state scheme and the VMC data, and provide a new picture to deal with the strongly correlated system. 相似文献
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In this paper we study the ground state phase diagram of a one-dimensional t-U-J model, at half-filling. In the large-bandwidth limit and for ferromagnetic exchange with easy-plane anisotropy, a phase with gapless charge and massive spin excitations, characterized by the coexistence of triplet superconducting and spin density wave instabilities is realized in the ground state. With reduction of the bandwidth, a transition into an insulating phase showing properties of the spin-
XY model takes place.Received: 6 February 2004, Published online: 9 April 2004PACS:
71.10.Hf Non-Fermi-liquid ground states, electron phase diagrams and phase transitions in model systems - 71.10.Fd Lattice fermion models (Hubbard model, etc.) - 74.20.Mn Nonconventional mechanisms (spin fluctuations, polarons and bipolarons, resonating valence bond model, anyon mechanism, marginal Fermi liquid, Luttinger liquid, etc.) - 71.27. + a Strongly correlated electron systems; heavy fermions - 75.10.Pq Spin chain modelsG.I. Japaridze: Permanent address: Andronikashvili Institute of Physics, Georgian Academy, Tamarashvili 6, Tbilisi 380077, Georgia 相似文献
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Layered organic superconductors are on the verge of the Mott insulator. We use the Gutzwiller variational method to study a two-dimensional Hubbard model including a spin exchange coupling term as a minimal model for the compounds. The ground state is found to be a Gossamer superconductor at small on-site Coulomb repulsion U and an antiferromagnetic Mott insulator at large U, separated by a first order phase transition. Our theory is qualitatively consistent with major experiments reported in organic superconductors. 相似文献
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We present a numerical study of the Hubbard-Holstein model in one dimension at half filling, including finite-frequency quantum phonons. At half filling, the effects of the electron-phonon and electron-electron interactions compete with the Holstein phonon coupling acting as an effective negative Hubbard on-site interaction U that promotes on-site electron pairs and a Peierls charge-density wave state. Most previous work on this model has assumed that only Peierls or Mott phases are possible at half filling. However, there has been speculation that a third metallic phase exists between the Peierls and Mott phases. We confirm the intermediate phase, and show that the Luttinger liquid correlation exponent K(rho) >1 in this region, indicating dominant superconducting pair correlations. We explore the full phase diagram as a function of Hubbard U, phonon coupling constant, and phonon frequency. 相似文献