We study strongly correlated electrons on a kagome lattice at 1/6 and 1/3 filling. They are described by an extended Hubbard Hamiltonian. We are concerned with the limit |t|<<V<<U with hopping amplitude t, nearest-neighbor repulsion V and on-site repulsion U. We derive an effective Hamiltonian and show, with the help of the Perron-Frobenius theorem, that the system is ferromagnetic at low temperatures. The robustness of ferromagnetism is discussed and extensions to other lattices are indicated.
Unconventional ferromagnetism and superconductivity in the imbalanced kagome-lattice Hubbard model are investigated by the mean-field theory and determinant quantum Monte Carlo method. Due to the asymmetric band structure of kagome lattice, the spin-$z$ ferromagnetic order intrinsically exists in the system, which is first enhanced by the interaction, and then continuously destructed after reaching a maximum at a moderate interaction strength. In contrast, the $xy$-plane ferromagnetism develops only above a critical interaction, which is estimated to be $U_c/t=3.65 \pm 0.05$ by finite-size sca…
The synthesis and characterization of the vanadium-based kagome metal TbV${_6}$Sn${_6}$ is presented. X-ray measurements confirm this material forms with the same crystal structure type as the recently investigated kagome metals GdV$_6$Sn$_6$ and YV$_6$Sn$_6$, with space group symmetry P6/mmm. A signature of a phase transition at 4.1K is observed in heat capacity, resistivity, and magnetic susceptibility measurements, and both resistivity and magnetization measurements exhibit hysteresis in magnetic field. Furthermore, a strikingly large anisotropy in the magnetic susceptibility was observed, …
Collinear ferromagnetism with reduced moment length in kagome magnet Nd3Ru4Al12
The University of Tokyo（东京大学）；Tokyo Metropolitan University（东京都立大学）；RIKEN Center for Emergent Matter Science (CEMS)（理化学研究所 新兴物质科学中心）；Gdańsk University of Technology（格但斯克理工大学）；The Institute for Solid State Physics, The University of Tokyo（东京大学固体物理研究所）；Universitas Indonesia（印度尼西亚大学）
Interaction in a flat band is magnified due to the divergence in the density of states, which gives rise to a variety of many-body phenomena such as ferromagnetism and Wigner crystallization. Until now, however, most studies of the flat band physics are based on model systems, making their experimental realization a distant future. Here, we propose a class of systems made of real atoms, namely, carbon atoms with realistic physical interactions (dubbed here as Kagome graphene/graphyne). Density functional theory calculations reveal that these Kagome lattices offer a controllable way to realize …
We study the quantum phase diagram of spinful fermions on kagome lattice with half-filled lowest flat bands. To understand the competition between magnetism, flat band frustration, and repulsive interactions, we adopt an extended $t$-$J$ model, where the hopping energy $t$, antiferromagnetic Heisenberg interaction $J$, and short-range neighboring Hubbard interaction $V$ are considered. In the weak $J$ regime, we identify a fully spin-polarized phase, which can further support the spontaneous Chern insulating phase driven by the short-range repulsive interaction. This phase still emerges with i…
We study two models of correlated bond- and site-disorder on the kagome lattice considering both translationally invariant and completely disordered systems. The models are shown to exhibit a perfectly flat ground state band in the presence of disorder for which we provide exact analytic solutions. Whereas in one model the flat band remains gapped and touches the dispersive band, the other model has a finite gap, demonstrating that the band touching is not protected by topology alone. Our model also displays fully saturated ferromagnetic groundstates in the presence of repulsive interactions, …
We consider the standard repulsive Hubbard model with a flat lowest-energy band for two one-dimensional lattices (diamond chain and ladder) as well as for a two-dimensional lattice (bilayer) at half filling of the flat band. The considered models do not fall in the class of Mielke-Tasaki flat-band ferromagnets, since they do not obey the connectivity conditions. However, the ground-state ferromagnetism can emerge, if the flat band becomes dispersive. To study this kinetic-energy-driven ferromagnetism we use perturbation theory and exact diagonalization of finite lattices. We find as a typical …
We consider the potential for novel forms of magnetism arising from the subtle interplay between electrons and spins in the under-screened kagome Kondo lattice model. At weak coupling, we show that incommensurate non-coplanar multi-wave vector magnetic orders arise at nearly all fillings and that this results from Fermi surface effects that introduces competing interactions between the spins. At strong coupling, we find that such complex order survives near half filling despite the presence of ferromagnetism at all other fillings. We show this arises due to state selection among a massive dege…
We examine instabilities of the plateau phases in the spin-1/2 kagome-lattice antiferromagnet in an applied field by means of degenerate perturbation theory, and find some emergent supersolid phases below the $m=5/9$ plateau. The wave functions of the plateau phases in a magnetic field have the particular construction based on the building blocks of resonating hexagons and their surrounding sites. Magnon excitations on each of these blocks suffer from a kinetic frustration effect, namely, they cannot hop easily to the others since the hopping amplitudes through the two paths destructively canc…
The flat band has attracted a lot of attention because it gives rise to many exotic phases, as recently demonstrated in magic angle twisted bilayer graphene. Here, based on first-principles calculations, we identify a metal-insulator transition in boron triangular Kagome lattice with a spin-polarized flat band at 2/3-filling. This phase transition is accompanied by the formation of a Wigner crystal, which is driven by Fermi surface nesting effect and thereby strong electron-phonon interactions, keeping ferromagnetism. Our calculation results suggest that boron triangular Kagome lattices with p…
We propose a new mechanism for quantum anomalous Hall (QAH) effect in the AB stacked MoTe$_2$/WSe$_2$ system. Based on the observation that the inter-layer tunneling is suppressed in the AB stacking, we consider a model with two layers coupled through the Coulomb interaction. The moiré lattices of the two layers are shifted to form a honeycomb lattice together. Initially, the system is in a layer-polarized Mott insulator at $ν_T=1$. But with a displacement field, an equal number of holes and electrons are doped into the two layers respectively and they form inter-layer exciton condensation. Th…
We perform extensive Monte Carlo simulations to investigate the dynamic phase transition properties of the two-dimensional kinetic Ising model on the kagome lattice in the presence of square-wave oscillating magnetic field. Through detailed finite-size scaling analysis, we study universality aspects of the non-equilibrium phase transition. Obtained critical exponents indicate that the two-dimensional kagome-lattice kinetic Ising model belongs to the same universality class with the corresponding Ising model in equilibrium. Moreover, dynamic critical exponent of the local moves used in simulati…
The Hubbard model on the kagome lattice is presently often considered as a minimal model to describe the rich low-temperature behavior of AV$_{3}$Sb$_{5}$ compounds (with A=K, Rb, Cs), including charge-density waves (CDWs), superconductivity, and possibly broken time-reversal symmetry. Here, we investigate, via variational Jastrow-Slater wave functions, the properties of its ground state when both onsite $U$ and nearest-neighbor $V$ Coulomb repulsions are considered at the van Hove filling. Our calculations reveal the presence of different interaction-driven CDWs and, contrary to previous reno…
Based on the density functional theory, we examine the origin of ferromagnetism in the Weyl semimetal Co$_3$Sn$_2$S$_2$ using different types of response theories. We argue that the magnetism of Co$_3$Sn$_2$S$_2$ has a dual nature and bears certain aspects of both itineracy and localization. On the one hand, the magnetism is soft, where the local magnetic moments strongly depend on temperature and the angles formed by these moments at different Co sites of the kagome lattice, as expected for itinerant magnets. On the other hand, the picture of localized spins still remains adequate for the des…
Performing an exact diagonalization of the effective spin problem, a ferromagnetic ground state of kinetic origin is shown to emerge in a system of $N$ strongly correlated electrons on a $L$-site ring ($L > N$). This phenomenon is brought about by the quantum necklace statistics originated from the no double occupancy constraint leading to a fractional shifted electron momentum quantization. As a consequence of such special energy level distribution, the kinetic ferromagnetism is stable only for $N=3$. For odd $N>3$ the fully polarized FM state energy is only a local minimum but it is protecte…
Quantum dimer model with extensive ground-state entropy on the kagome lattice
我们引入了一个量子二聚体模型的kagome晶格与动力学允许从3到6个二聚体共振周围的六边形。与先前研究的模型不同，不同的共振环出现不同的符号（由所涉及的二聚体数量的奇偶性给出）。这些符号在进行海森堡模型的最低阶重叠展开（Rokhsar and Kivelson 1988）时自然出现。我们证明了量子二聚体模型具有广泛的零温度熵和非常短的二聚体-二聚体关联。我们讨论了这种新的量子二聚体液体的自旋1/2海森堡模型的物理学上的戈薇晶格的可能相关性。
Magnetic structure and high-field magnetization of the distorted kagome lattice antiferromagnet Cs$_2$Cu$_3$SnF$_{12}$
Mahidol University（玛希隆大学）；ThEP, Commission of Higher Education（高等教育委员会理论物理中心）；Osaka Prefecture University（大阪府立大学）；Phranakhon Rajabhat University（佛统皇家大学）；Radboud University（拉德堡德大学）；Neutron Science Laboratory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK)（高能加速器研究机构物质结构科学研究所中子科学实验室）
We investigate the pressure evolution of the anomalous Hall effect in magnetic topological semimetal Co3Sn2S2 in diamond anvil cells with pressures up to 44.9-50.9 GPa. No evident trace of structural phase transition is detected through synchrotron x-ray diffraction over the measured pressure range of 0.2-50.9 GPa. We find that the anomalous Hall resistivity and the ferromagnetism are monotonically suppressed as increasing pressure and almost vanish around 22 GPa. The anomalous Hall conductivity varies non-monotonically against pressure at low temperatures, involving competition between origin…
Tunable Electronic Correlations in 135-Kagome Metals
Universität Würzburg（维尔茨堡大学）；CINECA；ESPCI Paris, PSL Research University, CNRS, Sorbonne Université（巴黎高等物理化工学院、PSL研究大学、法国国家科学研究中心、索邦大学）；Alma Mater Studiorum, University of Bologna（博洛尼亚大学）
Mott transition in the Hubbard model on the hyper-kagome lattice
基于最近对Na $_4$ Ir $_3$ O $_8$化合物的实验研究，我们采用动力学集团近似（DCA）方法（$N_c$ =12）结合连续时间量子蒙特卡罗（CT QMC）方法研究了“超kagome晶格”上的哈伯德模型.当Hubbard相互作用$U/W$（$W$是带宽）超过$T$ =0.1时的值1.2时，系统经历Mott转变，并且由于磁关联和电子的动能之间的竞争（由于几何阻挫）而显示重入行为。我们观察到一个“临界减速”的双人入住，这表明一个连续的过渡的证据。最近邻和次最近邻自旋-自旋关联表明，在我们的数值工具可以访问的温度范围内的弱耦合制度和反铁磁（AF）莫特绝缘体在强耦合制度的顺磁金属态。
We design from first principles a new type of two-dimensional metal-organic frameworks (MOFs) using phenalenyl-based ligands to exhibit a half-filled flat band of the kagome lattice, which is one of the lattice family that shows Lieb-Mielke-Tasaki's flat-band ferromagnetism. Among various MOFs, we find that $\textit{trans}$-Au-THTAP(trihydroxytriaminophenalenyl) has such an ideal band structure, where the Fermi energy is adjusted right at the flat band due to unpaired electrons of radical phenalenyl. The spin-orbit coupling opens a band gap giving a non-zero Chern number to the nearly flat ban…
We show that the interplay of a high density two-dimensional electron gas and localized electrons in a neighboring Mott insulator leads to kinetic magnetism unique to the Mott/band insulator interface. Our study is based upon a bilayer Hubbard model at $U=\infty$ with a potential difference between the two layers. We combine analytic results with DMRG simulations to show that magnetism, and especially ferromagnetism, is greatly enhanced relative by the proximity of the two subsystems. The results are potentially relevant to recent experiments suggesting magnetism in $R$TiO$_3$/SrTiO$_3$ hetero…
