Structural phase transition accompanying with quadrupolar ordering in DyB4 with Shastry-Sutherland type geometrical frustration has been studied by X-ray diffraction. Previous study [D. Okuyama et al.: J. Phys. Soc. Jpn. 74 (2005) 2434.] using resonant X-ray scattering revealed short-range ordering of the Ozx-type quadrupolar moments and the c-plane component of the magnetic moments in addition to long-range ordering of the c-axis component of the magnetic moments. The present report focuses on the lattice distortion below the quadrupolar ordering temperature at TN2=12.7 K. The (0 0 l=integer) fundamental lattice reflection splits into four peaks along the h and k directions and the (h=even 0 0) reflection becomes broad along the l direction. This indicates that a structural transition from tetragonal to monoclinic takes place below TN2 together with the ordering of the quadrupolar moments.
The small-cluster exact-diagonalization calculations and the projector quantum Monte Carlo method are used to examine the competing effects of geometrical frustration and interaction on ferromagnetism in the Hubbard model on the Shastry-Sutherland lattice. It is shown that the geometrical frustration stabilizes the ferromagnetic state at high electron concentrations ($n \gtrsim 7/4$), where strong correlations between ferromagnetism and the shape of the noninteracting density of states are observed. In particular, it is found that ferromagnetism is stabilized only for these values of frustrati…
Impact of geometrical frustration on charge transport near the Mott transition in pyrochlore (Y$_{1-x}$Cd$_{x}$)$_{2}$Mo$_{2}$O$_{7}$
为了探索阻挫晶格强关联电子系统中的新的自旋-电荷耦合现象，研究了烧绿石结构空穴掺杂自旋玻璃（Mott）绝缘体（Y $_{1-x}$ Cd $_{x}$）$_{2}$ Mo $_{2}$ O $_{7}$的电荷输运和动力学.在空穴掺杂导致自旋玻璃态消失的同时，出现了具有强重整化电子质量的扩散金属输运，这种输运没有长程自旋有序，这是由几何阻挫引起的强反铁磁自旋涨落引起的.
Geometrical frustration describes situations where interactions are incompatible with the lattice geometry and stabilizes exotic phases such as spin liquids. Whether geometrical frustration of magnetic interactions in metals can induce unconventional quantum critical points is an active area of research. We focus on the hexagonal heavy fermion metal CeRhSn where the Kondo ions are located on distorted kagome planes stacked along the c axis. Low-temperature specific heat, thermal expansion and magnetic Grüneisen parameter measurements prove a zero-field quantum critical point. The linear therma…
Hexagonal CeRhSn with paramagnetic $4f$ moments on a distorted Kagome lattice displays zero-field quantum critical behavior related to geometrical frustration. We report high-resolution thermal expansion and magnetostriction measurements under multiextreme conditions such as uniaxial stress up to 200 MPa, temperatures down to 0.1 K and magnetic fields up to 10 T. Under uniaxial stress along the $a$-direction, quantum criticality disappears and a complex magnetic phase diagram arises with a sequence of phases below 1.2 K and fields between 0 and 3 T ($\parallel a$). Since the Kondo coupling inc…
Geometrically Frustrated Quadrupoles on the Pyrochlore Lattice and Generalized Spin Liquids
Max Planck Institute for the Physics of Complex Systems（马克斯·普朗克复杂系统物理研究所）；Laboratoire Léon Brillouin, CEA, CNRS, Université Paris-Saclay（里昂·布里渊实验室，法国原子能和替代能源委员会，法国国家科学研究中心，巴黎萨克雷大学）；Université Grenoble Alpes, CNRS, Institut Néel（格勒诺布尔阿尔卑斯大学，法国国家科学研究中心，尼尔研究所）
We calculated the phase diagram of the Kondo-Heisenberg model on two-dimensional honeycomb lattice with both nearest-neighbor and next-nearest-neighbor antiferromagnetic spin exchanges, to investigate the interplay between RKKY and Kondo interactions at presence of magnetic frustration. Within a mean-field decoupling technology in slave-fermion representation, we derived the zero-temperature phase diagram as a function of Kondo coupling $J_k$ and frustration strength $Q$. The geometrical frustration can destroy the magnetic order, driving the original antiferromagnetic (AF) phase to non-magnet…
The origin of non-collinear magnetic order in UO$_{2}$ is studied by an ab initio dynamical-mean-field-theory framework in conjunction with a linear-response approach for evaluating inter-site superexchange interactions between U 5$f^{2}$ shells. The calculated quadrupole-quadruple superexchange interactions are found to unambiguously resolve the frustration of face-centered-cubic U sublattice toward stabilization of the experimentally observed non-collinear 3k-magnetic order. Therefore, the exotic 3k antiferromagnetic order in UO$_{2}$ can be accounted for by a purely electronic exchange mech…
Dimensionality is a critical factor in determining the properties of solids and is an apparent built-in character of the crystal structure. However, it can be an emergent and tunable property in geometrically frustrated spin systems. Here, we study the spin dynamics of the tetrahedral cluster antiferromagnet, pharmacosiderite, via muon spin resonance and neutron scattering. We find that the spin correlation exhibits a two-dimensional characteristic despite the isotropic connectivity of tetrahedral clusters made of spin 5/2 Fe3+ ions in the three-dimensional cubic crystal, which we ascribe to t…
The geometrically frustrated antiferromagnetic Swedenborgite DyBaCo$_{4}$O$_{7}$ is investigated by a combination of xray diffraction, magnetization and dielectric measurements. Systematic doping in the series Dy$_{1-x}$Ca$_{x}$BaCo$_{4}$O$_{7}$ causes a lifting of the geometrical frustration resulting in a structural transition from a Trigonal P31c to an orthorhombic Pbn2$_{1 }$ symmetry at $x=0.4$. This structural transition can also be accessed as a function of temperature, and all our orthorhombic specimens exhibit this transition at elevated temperatures. In line with previous reports, th…
Competition between Geometrical Frustration and the Kondo Effect in CePdAl Revealed by High-Resolution Magnetization
Institute for Solid State Physics, The University of Tokyo（东京大学固体物理研究所）；Nagoya Institute of Technology（名古屋工业大学）；Institute for Materials Research, Tohoku University（东北大学物质材料研究所）；School of Science and Engineering, Chuo University（中央理工学院）；Department of Basic Science, The University of Tokyo（东京大学基础科学系）；Graduate School of Science and Engineering, Univ. of Toyama（富山理工学研究院）
Magnetostrictive Neel ordering of the spin-5/2 ladder compound BaMn2O3: distortion-induced lifting of geometrical frustration
本文用热力学和衍射技术研究了BaMn $_2$ O $_3$的晶体结构和磁性。BaMn $_2$ O $_3$是$S = 5/2$自旋阶梯的实现，因为磁性相互作用沿着形成阶梯的腿和横档的180个$^\circ$ Mn-O-Mn键占主导地位。的磁化率的温度依赖性表现出良好定义的最大值为所有方向证明低维磁字符在BaMn $_2$ O $_3$。然而，磁化率和粉末中子衍射数据表明，BaMn $_2$ O $_3$在184 K时表现出向反铁磁有序的转变，尽管在正交高温相中最近邻的梯间耦合完全受挫。这种挫败感被伴随着磁性转变的非常强烈的单斜畸变所解除。
The geometrically-frustrated, triangular antiferromagnet GGG exhibits a rich mix of short-range order and isolated quantum states. We investigate the effects of up to 1% Neodymium substitution for Gallium on the ac magnetic response at temperatures below 1 K in both the linear and nonlinear regimes. Substitutional disorder actually drives the system towards a more perfectly frustrated state, apparently compensating for the effect of imperfect Gadolinium/Gallium stoichiometry, while at the same time more closely demarcating the boundaries of isolated, coherent clusters composed of hundreds of s…
Spontaneous charge ordering occurring in correlated systems may be considered as a possible route to generate effective lattice structures with unconventional couplings. For this purpose we investigate the phase diagram of doped extended Hubbard models on two lattices: (i) the honeycomb lattice with on-site $U$ and nearest-neighbor $V$ Coulomb interactions at $3/4$ filling ($n=3/2$) and (ii) the triangular lattice with on-site $U$, nearest-neighbor $V$, and next-nearest-neighbor $V'$ Coulomb interactions at $3/8$ filling ($n=3/4$). We consider various approaches including mean-field approximat…
In the present study we investigate the effects of geometrical frustration on the XY model with antiferromagnetic (AFM) coupling on a triangular lattice, generalized by the inclusion of a third-order antinematic term (AN3). We demonstrate that at non-zero temperatures such a generalization leads to a phase diagram consisting of three different quasi-long-range ordered (QLRO) phases. Compared to the model with the second-order AN coupling (AN2), it includes besides the AFM and AN3 phases which appear in the limits of relatively strong AFM and AN3 interactions, respectively, an additional comple…
Recently, Co-based honeycomb magnets have been proposed as promising candidate materials to host the Kitaev spin liquid state. One of the front-runners is BaCo$_2$(AsO$_4$)$_2$ (BCAO), where it was suggested that the exchange processes between Co$^{2+}$ ions via the surrounding edge-sharing oxygen octahedra could give rise to bond-dependent Kitaev interactions. In this work, we present and analyze comprehensive inelastic neutron scattering studies of BCAO with fields in the honeycomb plane. Combining the constraints from the magnon excitations in the high-field polarized state and the inelasti…
Nonmagnetic Insulating States near the Mott Transitions on Lattices with Geometrical Frustration and Implications for $κ$-(ET)$_2$Cu$_2(CN)_3$
我们研究了各向异性三角晶格上的哈伯德模型的相图，它也代表了$κ$型BEDT-TTF化合物的模型。与平均场预测相反，路径积分重整化群计算显示了普遍存在的反铁磁绝缘体和顺磁金属的三明治绝缘体。超导相没有像磁通相那样出现简单的平移对称破缺，这意味着它是一个真正的莫特绝缘体。我们讨论了在$κ$ -（ET）$_2$ Cu $_2(CN)_3$中发现的绝缘相的可能相关性。
We systematically derive low-energy effective Hamiltonians for molecular solids $β^\prime$-$X$[Pd(dmit)$_{2}$]$_{2}$ ($X$ represents a cation) using ab initio density functional theory calculations and clarify how the cation controls the inter-dimer transfer integrals and the interaction parameters. The effective models are solved using the exact diagonalization method and the antiferromagnetic ordered moment is shown to be significantly suppressed around the spin-liquid candidate of $X$=EtMe$_{3}$Sb, which is reported in experiments. We also show that both the geometrical frustration and the …
We report on the emergence of antiferromagnetic spin chains from two-dimensionally aligned spins on the anisotropic triangular lattice (ATL) in the insulating calcium rhenium oxychloride Ca3ReO5Cl2. The compound contains Re6+ ions each with one unpaired electron in the dxy orbital, which are arranged to form a spin-1/2 ATL with J'/J ~ 0.32 and J = 41 K, where J and J' are magnetic interactions in and between the chains, respectively. In spite of the apparent two dimensionality, we observe clear evidence of a gapless spin liquid that is characteristic of the spin-1/2 Heisenberg chain. This one-…
Magnetic frustration, which is well-defined in insulating systems with localized magnetic moments, yields exotic ground states like spin ices, spin glasses, or spin liquids. In metals magnetic frustration is less well defined because of the incipient delocalization of magnetic moments by the interaction with conduction electrons, viz., the Kondo effect. Hence, the Kondo effect and magnetic frustration are antithetic phenomena. Here we present experimental data of electrical resistivity, magnetization, specific heat and neutron diffraction on CePdAl, which is one of the rare examples of a geome…
The local atomic and magnetic structures of the compounds $A$MnO$_2$ ($A$ = Na, Cu), which realize a geometrically frustrated, spatially anisotropic triangular lattice of Mn spins, have been investigated by atomic and magnetic pair distribution function analysis of neutron total scattering data. Relief of frustration in CuMnO$_2$ is accompanied by a conventional cooperative symmetry-lowering lattice distortion driven by Néel order. In NaMnO$_2$, however, the distortion has a short-range nature. A cooperative interaction between the locally broken symmetry and short-range magnetic correlations …
Spin Frustration and Orbital Order in Vanadium Spinels
本文介绍了钒尖晶石氧化物$A$ V $_2$ O $_4$（$A$ = Zn、Mg或Cd）中的几何阻挫效应和自旋与轨道自由度之间的相互作用的理论研究结果。在强关联极限下引入一个有效的自旋-轨道-晶格耦合模型，并对该模型进行蒙特卡罗模拟，提出了一个轨道有序相的约化自旋哈密顿量，以捕捉反铁磁有序的稳定机制.轨道序通过在自旋交换相互作用中引入空间各向异性大大降低了自旋阻挫，约化自旋模型可以看作是弱耦合的一维反铁磁链.通过有限尺寸标度分析得到的临界指数表明，磁跃迁属于三维海森堡普适类。平均场能级中剩余的挫折通过热涨落来减少，以稳定共线有序。
We explore the magnetic phases in a Kondo lattice model on the geometrically frustrated Shastry-Sutherland lattice at metallic electron densities, searching for noncollinear and noncoplanar spin textures. Motivated by experimental observations in many rare-earth-based frustrated metallic magnets, we treat the local moments as classical spins and set the coupling between the itinerant electrons and local moments as the largest energy scale in the problem. Our results show that a noncollinear flux state is stabilized over an extended range of Hamiltonian parameters. These spin states can be quen…
To verify the effect of geometrical frustration, we artificially distort the triangular lattice of quasi-two-dimensional organic conductor $κ$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ [BEDT-TTF: bis(ethylenedithio)terathiofulvalene] by analogous-molecular substitution and apply $^{13}$C NMR of bulk and substituted sites, electric conductivity, and static magnetic susceptibility measurements. The results indicate that the magnetic characteristics of the substituted sample are quantitatively similar to those of the pure sample. Moreover the magnetic characteristics at the substituted sites are also the same…
Frustration in quantum spin systems promote a variety of novel quantum phases. An important example is the frustrated spin-$1$ model on the square lattice with the nearest-neighbor bilinear ($J_1$) and biquadratic ($K_1$) interactions. We provide strong evidence for a nematic spin liquid phase in a range of $K_1/J_1$ near the SU(3)-symmetric point ($J_1 = K_1$), based on the linear flavor-wave theory and extensive density matrix renormalization group calculation. This phase displays no spin dipolar or quadrupolar order, preserves translational symmetry but spontaneously breaks $C_4$ lattice ro…
