The antiferromagnetic phase of two-dimensional (2D) and three-dimensional (3D) Hubbard model with nearest neighbors hopping is studied on a bipartite cubic lattice by means of the quantum SU(2)xU(1) rotor approach that yields a fully self-consistent treatment of the antiferromagnetic state that respects the symmetry properties the model and satisfy the Mermin-Wagner theorem. The collective variables for charge and spin are isolated in the form of the space-time fluctuating U(1) phase field and rotating spin quantization axis governed by the SU(2) symmetry, respectively. As a result interacting electrons appear as a composite objects consisting of bare fermions with attached U(1) and SU(2) gauge fields. An effective action consisting of a spin-charge rotor and a fermionic fields is derived as a function of the Coulomb repulsion U and hopping parameter t. At zero temperature, our theory describes the evolution from a Slater (U<<t) to a Mott-Heisenberg (U>>t) antiferromagnet. The results for zero-temperature sublatice magnetization (2D) and finite temperature (3D) phase diagram of the antiferromagnetic Hubbard model as a function of the crossover parameter U/t are presented and the role of the spin Berry phase in the interaction driven crossover is analyzed.
Diagrammatic Monte Carlo -- the technique for numerically exact summation of all Feynman diagrams to high orders -- offers a unique unbiased probe of continuous phase transitions. Being formulated directly in the thermodynamic limit, the diagrammatic series is bound to diverge and is not resummable at the transition due to the non-analyticity of physical observables. This enables the detection of the transition with controlled error bars from an analysis of the series coefficients alone, avoiding the challenge of evaluating physical observables near the transition. We demonstrate this techniqu…
受最近数值结果的启发，我们研究了Kane-Mele-Hubbard（KHM）模型的相图，特别是它的量子临界点的性质。Kane-Mele-哈伯德模型的相图可以通过打破我们以前工作的SO（4）对称性而理解为U（1）_spin x U（1）_charge x PH对称性。面内Neel相的涡旋携带电荷，带电磁涡旋的扩散驱动面内Neel相和QSH绝缘体相之间的转变，这种转变属于3dXY普适类。液相和面内Neel相之间的转变是各向异性的O（4）转变，由于量子涨落，该转变最终变为一级。根据1/N计算，预测液态-QSH相变为一级相变。
Crossover from weakly to strongly correlated regions in the two-dimensional Hubbard model -- Off-diagonal wave function Monte Carlo studies of Hubbard model II --
We report on the epitaxial strain-driven electronic and antiferromagnetic modulations of a pseudospin-half square lattice realized in superlattices of (SrIrO3)1/(SrTiO3)1. With increasing compressive strain, we find the low-temperature insulating behavior to be strongly suppressed with a corresponding systematic reduction of both the Neel temperature and the staggered moment. However, despite such a suppression, the system remains weakly insulating above the Neel transition. The emergence of metallicity is observed under large compressive strain but only at temperatures far above the Néel tran…
The ground state of the Hubbard model with nearest-neighbor hopping on the square lattice at half filling is known to be that of an antiferromagnetic (AFM) band insulator for any on-site repulsion. At finite temperature, the absence of long-range order makes the question of how the interaction-driven insulator is realized nontrivial. We address this problem with controlled accuracy in the thermodynamic limit using self-energy diagrammatic determinant Monte Carlo and dynamical cluster approximation methods and show that development of long-range AFM correlations drives an extended crossover fro…
Symmetry crossover and excitation thresholds at the neutral-ionic transition of the modified Hubbard model
用价键方法计算了均匀间距的N位修正哈伯德模型的基态、电荷密度和激发能。在中性-离子跃迁（NIT）时，基态分别在周期和反周期边界条件下的4 n，4 n +2环中发生对称性交叉.改进的哈伯德模型在成对侧的抗磁性带绝缘体和共价侧的顺磁性莫特绝缘体之间具有连续的NIT。对于有限N的单重态-三重态（ST）、单重态-单重态（SS）和电荷能隙表明，随着U的增加，ST和SS能隙在NIT处闭合，并且电荷能隙仅在那里消失。双N激励将所有奇点约束到对称交叉的约0.1t。NIT被解释为一个本地化的基态（gs）与有限的间隙对侧和扩展的GS与消失的ST和SS的共价侧的间隙。电荷间隙和电荷刚度表明在过渡金属GS，然而，是无条件不稳定的二聚。
Magnetic correlations and pairing in the 1/5-depleted square lattice Hubbard model
我们研究了单轨道哈伯德模型上的1/5耗尽的正方形晶格几何形状，出现在这样的不同系统的自旋间隙磁绝缘体CaV 4 O 9和有序空位铁硒化物，提出了新的问题，在这些材料的磁有序和超导性的起源。我们发现一个丰富的相图，包括一个元胞单重态相，二聚体单重态相，尼尔和块自旋反铁磁相，条纹相。量子蒙特卡罗模拟结果表明，在半填充时，主要的配对关联从元胞相的d波转变为向Neel相转变时的扩展s波。这些发现与铁基超导体有着有趣的联系，并表明多轨道系统的一些物理学可以在不同的掺杂下被单轨道模型捕获。
Metallic Néel order stabilized by coupling between inequivalent Hubbard layers
Institute for Advanced Study in Physics, Zhejiang University（浙江大学前沿物理研究院）；Leinweber Institute for Theoretical Physics, Stanford University（斯坦福大学莱因韦伯理论物理研究所）；Department of Applied Physics, Stanford University（斯坦福大学应用物理系）；Institute for Advanced Study, Tsinghua University（清华大学高等研究院）；Department of Physics, Stanford University（斯坦福大学物理系）
Pairing order and condensate fraction across the BCS-BEC crossover in the two-dimensional attractive Hubbard model
Institute of Modern Physics, Northwest University（西北大学现代物理研究所）；School of Physics, Northwest University（西北大学物理学院）；Shaanxi Key Laboratory for Theoretical Physics Frontiers（陕西理论物理前沿重点实验室）；Fundamental Discipline Research Center for Quantum Science and Technology of Shaanxi Province（陕西省量子科学与技术基础学科研究中心）；Hefei National Laboratory（合肥国家实验室）
Motivated by dimensional crossover in layered organic $κ$ salts, we determine the phase diagram of a system of four periodically coupled Hubbard chains with frustration at half filling as a function of the interchain hopping ${t_{\perp}/t}$ and interaction strength ${U/t}$ at a fixed ratio of frustration and interchain hopping ${t'/t_{\perp}=-0.5}$. We cover the range from the one-dimensional limit of uncoupled chains (${t_{\perp}/t=0.0}$) to the isotropic model (${t_{\perp}/t=1.0}$). For strong ${U/t}$, we find an antiferromagnetic insulator; in the weak-to-moderate-interaction regime, the ph…
The electronic properties of excitonic insulators have been examined precisely in recent years. Pictures of exciton condensation may be applied to the spin-state transition observed in perovskite cobalt oxides. We examine the crystal-field and magnetic-field dependences of spatial spin structures on the basis of the density matrix renormalization group method using an effective model for the one-dimensional two-orbital Hubbard model in strong-coupling limit. We find an excitonic insulating (EI) phase and a spin-state ordering (SSO) phase in the intermediate region between low-spin and high-spi…
The $2d$ Hubbard model with nearest-neighbour hopping on the square lattice and an average of one electron per site is known to undergo an extended crossover from metallic to insulating behavior driven by proliferating antiferromagnetic correlations. We study signatures of this crossover in spin and charge correlation functions and present results obtained with controlled accuracy using diagrammatic Monte Carlo in the range of parameters amenable to experimental verification with ultracold atoms in optical lattices. The qualitative changes in charge and spin correlations associated with the cr…
Thermal Signatures of the Slater-Mott Crossover in the Hubbard Model: From Double Occupancy to Antiferromagnetic Correlation Length
University of Science and Technology of China（中国科学技术大学）；Institute of Modern Physics, Northwest University（西北大学现代物理研究所）；Hefei National Laboratory for Physical Sciences at Microscale（合肥微尺度物质科学国家研究中心）；Hefei National Laboratory（合肥国家实验室）；Shaanxi Key Laboratory for Theoretical Physics Frontiers（陕西省理论物理前沿重点实验室）；Fundamental Discipline Research Center for Quantum Science and Technology of Shaanxi Province（陕西省量子科学与技术基础学科研究中心）
Half-filled Hubbard Model on a Bethe lattice with next-nearest neighbor hopping
研究了具有最近邻和次最近邻跃迁$t_1$和$t_2$的Bethe晶格上Néel反铁磁性与顺磁金属-绝缘体跃迁（PMIT）之间的相互作用.我们在本文中集中在半填充的情况。对于$t_2/t_1\to 1$，PMIT超过反铁磁相，并显示出类似于V $_2$ O $_3$的情况。在这个参数制度，我们还观察到一个新的磁相。
