One-Dimensional Spin-Liquid without Magnon Excitations [Phys. Rev. Lett. 78, 3939 (1997)] (original) (raw)
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One-Dimensional Spin-Liquid without Magnon Excitations
Physical Review Letters, 1997
It is shown that a sufficiently strong four-spin interaction in the spin-1/2 spin ladder can cause dimerization. Such interaction can be generated either by phonons or (in the doped state) by the conventional Coulomb repulsion between the holes. The dimerized phases are thermodynamically undistinguishable from the Haldane phase, but have dramatically different correlation functions: the dynamical magnetic susceptibility, instead of displaying a sharp single magnon peak near q=piq = \piq=pi, shows only a two-particle threshold separated from the ground state by a gap.
From magnetism to one-dimensional spin liquid in the anisotropic triangular lattice
We investigate the anisotropic triangular lattice that interpolates from decoupled one-dimensional chains to the isotropic triangular lattice and has been suggested to be relevant for various quasitwo-dimensional materials, such as Cs2CuCl4 or κ-(ET)2Cu2(CN)3, an organic material that shows intriguing magnetic properties. We obtain an excellent accuracy by means of a novel representation for the resonating valence bond wave function with both singlet and triplet pairing. This approach allows us to establish that the magnetic order is rapidly destroyed away from the pure triangular lattice and incommensurate spin correlations are short range. A non-magnetic spin liquid naturally emerges in a wide range of the phase diagram, with strong one-dimensional character. The relevance of the triplet pairing for κ-(ET)2Cu2(CN)3 is also discussed. PACS numbers: 75.10.-b, 71.10.Pm,75.40.Mg
A one-dimensional liquid of fermions with tunable spin
Nature Physics, 2014
Correlations in systems with spin degree of freedom are at the heart of fundamental phenomena, ranging from magnetism to superconductivity. The effects of correlations depend strongly on dimensionality, a striking example being onedimensional (1D) electronic systems, extensively studied theoretically over the past fifty years . However, the experimental investigation of the role of spin multiplicity in 1D fermionsand especially for more than two spin components -is still lacking. Here we report on the realization of 1D, strongly-correlated liquids of ultracold fermions interacting repulsively within SU(N ) symmetry, with a tunable number N of spin components. We observe that static and dynamic properties of the system deviate from those of ideal fermions and, for N > 2, from those of a spin-1/2 Luttinger liquid. In the large-N limit, the system exhibits properties of a bosonic spinless liquid. Our results provide a testing ground for many-body theories and may lead to the observation of fundamental 1D effects .
A new paradigm for two-dimensional spin liquids
Journal of Applied Physics, 1998
Motivated by the geometry of the materials Na2Ti2As2O and Na2Ti2Sb2O, we study a square-lattice Heisenberg antiferromagnet, with spins located at the bond-centers. The largest exchange constant J couples neighboring spins in a given row or column. This leads to a mesh of isolated spin-chains running along the X and Y axes. A weaker exchange constant J ′ couples the nearest-neighbor spins on the lattice. Classically, J ′ fails to fix the relative spin orientation for different chains and hence the ground state is highly degenerate. Quantum order by disorder effect is studied by spin-wave theory and numerical methods. It is shown that a 4-sublattice order is favored by quantum fluctuations. However, several arguments are presented that suggest that the ground state of the system remains disordered, thus providing us with a paradigm for a two-dimensional spin-liquid.
Physical Review B, 2014
We investigate the Hubbard model on the anisotropic triangular lattice with two hopping parameters t and t ′ in different spatial directions, interpolating between decoupled chains (t = 0) and the isotropic triangular lattice (t = t ′ ). Variational wave functions that include both Jastrow and backflow terms are used to compare spin-liquid and magnetic phases with different pitch vectors describing both collinear and coplanar (spiral) order. For relatively large values of the on-site interaction U/t ′ 10 and substantial frustration, i.e., 0.3 t/t ′ 0.8, the spin-liquid state is clearly favored over magnetic states. Spiral magnetic order is only stable in the vicinity of the isotropic point, while collinear order is obtained in a wide range of inter-chain hoppings from small to intermediate frustration.
Physical Review B, 2019
The mixed spin-1 and spin-1/2 Heisenberg octahedral chain with regularly alternating monomeric spin-1 sites and square-plaquette spin-1/2 sites is investigated using variational technique, localizedmagnon approach, exact diagonalization (ED) and density-matrix renormalization group (DMRG) method. The investigated model has in a magnetic field an extraordinarily rich ground-state phase diagram, which includes the uniform and cluster-based Haldane phases, two ferrimagnetic phases of Lieb-Mattis type, two quantum spin liquids and two bound magnon crystals in addition to the fully polarized ferromagnetic phase. The lowest-energy eigenstates in a highly-frustrated parameter region belong to flat bands and hence, low-temperature thermodynamics above the bound magnoncrystal ground states can be satisfactorily described within the localized-magnon approach. The variational method provides an exact evidence for the magnon-crystal phase with a character of the monomer-tetramer ground state at zero field, while another magnon-crystal phase with a single bound magnon at each square plaquette is found in a high-field region. A diversity of quantum ground states gives rise to manifold zero-temperature magnetization curves, which may involve up to four wide intermediate plateaus at zero, one-sixth, one-third and two-thirds of the saturation magnetization, two quantum spin-liquid regions and two tiny plateaus at one-ninth and one-twelfth of the saturation magnetization corresponding to the fragmentized cluster-based Haldane phases.
2007
We study theoretically the destruction of spin nematic order due to quantum fluctuations in quasi-one dimensional spin-1 magnets. If the nematic ordering is disordered by condensing disclinations then quantum Berry phase effects induce dimerization in the resulting paramagnet. We develop a theory for a Landau-forbidden second order transition between the spin nematic and dimerized states found in recent numerical calculations. Numerical tests of the theory are suggested.
Excitations of a Low-Dimensional Dimerized Spin Ladder Under a Magnetic Field
International Journal of Modern Physics B, 2007
Here we study the dimerized spin ladder with nearest-neighbor (J1) and next-nearest-neighbor (J2) anti-ferromagnetic interaction under a magnetic field. We predict the existence of different magnetization plateaus for the presence of spin-Peierls interaction on both J1 and J2. Magnetization plateau at m = 0 for J1 dimerization is spontaneous due to XY interaction, but it is absent for J2 dimerization, only intrinsic umklapp term leads to plateau (spin gap) state for some specific values of XXZ anisotropy (Δ) and J2. Here we predict a saturation plateau which is the classical phase of the system. There are some numerical support of our analytical approach already existing in the literature. The transition from commensurate gapped phase to incommensurate Luttinger liquid phase is the Mott-δ type of transition.
Thermodynamic behavior near the quantum orders in dimerized spin S = 1/2 two-leg ladders
Journal of Magnetism and Magnetic Materials, 2017
Thermodynamic properties of spin-1/2 Heisenberg antiferromagnetic (AFM) two-leg ladder with alternating strong rung interactions are investigated by numerical and analytical approaches. Two gapless Luttinger Liquid (LL) and two gapped symmetry protected topological (SPT) phases are observed in this type of spin structure. As a low temperature characteristic of the first LL gapless regime, a maximum and a minimum are observed in the magnetization curve. The magnetization of the system in the second LL phase is completely different and shows only a maximum in the temperature behavior. In the SPT Haldane phase, the value of magnetization increases with single broad peak, while apparently anomalous behavior is observed in the SPT 1/2-plateau phase. In fact, we have argued that the magnetization shows a complex logical temperature behavior in the 1/2plateau phase. In the second LL phase, there is a novel three peaks structure in the temperature behaviour of the specific heat whereas in the first LL phase, specific heat shows a double peaks structure. The temperature dependence of thermodynamic quantities like the magnetization, the susceptibility and the specific heat are also studied to specify various SPT and LL phases.