Magnetic Field Induced Exotic Phases in Isotropic Frustrated Spin-1/2 chain (original) (raw)
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Vector Chiral Phases in the Frustrated 2D XY Model and Quantum Spin Chains
Physical Review Letters, 2014
The phase diagram of the frustrated 2D classical and 1D quantum XY models is calculated analytically. Four transitions are found: the vortex unbinding transitions triggered by strong fluctuations occur above and below the chiral transition temperature. Vortex interaction is short range on small and logarithmic on large scales. The chiral transition, though belonging to the Ising universality class by symmetry, has different critical exponents due to nonlocal interaction. In a narrow region close to the Lifshitz point a reentrant phase transition between paramagnetic and quasiferromagnetic phase appears. Applications to antiferromagnetic quantum spin chains and multiferroics are discussed.
Vector Chiral Phases in the Frustrated 2DXYModel and Quantum Spin Chains
Physical Review Letters, 2014
The phase diagram of the frustrated 2D classical and 1D quantum XY models is calculated analytically. Four transitions are found: the vortex unbinding transitions triggered by strong fluctuations occur above and below the chiral transition temperature. Vortex interaction is short range on small and logarithmic on large scales. The chiral transition, though belonging to the Ising universality class by symmetry, has a different critical exponents due to non-local interaction. In a narrow region close to the Lifshitz point a reentrant phase transition between paramagnetic and quasi-ferromagnetic phase appears. Applications to antiferromagnetic quantum spin chains and multi-ferroics are discussed.
Multipolar phase in frustrated spin-1/2 and spin-1 chains
Physical Review B, 2017
The J1 − J2 spin chain model with nearest neighbor J1 and next nearest neighbor antiferromagnetic J2 interaction is one of the most popular frustrated magnetic models. This model system has been extensively studied theoretically and applied to explain the magnetic properties of the real low-dimensional materials. However, existence of different phases for the J1 − J2 model in an axial magnetic field h is either not understood or has been controversial. In this paper we show the existence of higher order p > 4 multipolar phase near the critical point (J2/J1)c = −0.25. The criterion to detect the quadrupolar or spin nematic (SN)/spin density wave of type two (SDW2) phase using the inelastic neutron scattering (INS) experiment data is also discussed, and INS data of LiCuVO4 compound is modelled. We discuss the dimerized and degenerate ground state in the quadrupolar phase. The major contribution of binding energy in the spin-1/2 system comes from the longitudinal component of the nearest neighbor bonds. We also study spin nematic/SDW2 phase in spin-1 system in large J2/J1 limit.
Journal of physics. Condensed matter : an Institute of Physics journal, 2016
The spin-1/2 chain with isotropic exchange J 1, J 2 > 0 between first and second neighbors is frustrated for either sign of J 1 and has a singlet ground state (GS) for J 1/J 2 ⩾ -4. Its rich quantum phase diagram supports gapless, gapped, commensurate (C), incommensurate (IC) and other phases. Critical points J 1/J 2 are evaluated using exact diagonalization and density matrix renormalization group calculations. The wave vector q G of spin correlations is related to GS degeneracy and obtained as the peak of the spin structure factor S(q). Variable q G indicates IC phases in two J 1/J 2 intervals, [-4, - 1.24] and [0.44, 2], and a C-IC point at J 1/J 2 = 2. The decoupled C phase in [-1.24, 0.44] has constant q G = π/2, nondegenerate GS, and a lowest triplet state with broken spin density on sublattices of odd and even numbered sites. The lowest triplet and singlet excitations, E m and E σ , are degenerate in finite systems at specific frustration J 1/J 2. Level crossing e...
2006
The frustrated ferromagnetic spin-1∕2 Heisenberg chain is studied by means of a low-energy field theory as well as the density-matrix renormalization group and exact diagonalization methods. First, we study the ground-state phase diagram in a magnetic field and find an “even-odd” (EO) phase characterized by bound pairs of magnons in the region of two weakly coupled antiferromagnetic chains. A jump in the magnetization curves signals a first-order transition at the boundary of the EO phase, but otherwise the curves are smooth. Second, we discuss thermodynamic properties at zero field, where we confirm a double-peak structure in the specific heat for moderate frustrating next-nearest-neighbor interactions.
Physical Review B, 2012
We study the ground-state (GS) properties of the frustrated spin-1 2 J 1-J 2-J 3 Heisenberg model on the two-dimensional honeycomb lattice with ferromagnetic nearest-neighbor (J 1 = −1) exchange and frustrating antiferromagnetic next-nearest-neighbor (J 2 > 0) and next-next-nearest-neighbor (J 3 > 0) exchanges, for the case J 3 = J 2. We use the coupled-cluster method implemented to high orders of approximation, complemented by the Lanczos exact diagonalization of a large finite lattice with 32 sites, in order to calculate the GS energy, magnetic order parameter, and spin-spin correlation functions. In one scenario we find a quantum phase transition point between regions characterized by ferromagnetic order and a form of antiferromagnetic ("striped") collinear order at J c 2 ≈ 0.1095 ± 0.0005, which is below the corresponding hypothetical transition point at J cl 2 = 1 7 (≈0.143) for the classical version of the model, in which we momentarily ignore the intervening noncollinear spiral phase in the region 1 10 < J 2 < 1 5. Hence we see that quantum fluctuations appear to stabilize somewhat the collinear antiferromagnetic order in preference to the ferromagnetic order in this model. We compare results for the present ferromagnetic case (with J 1 = −1) to previous results for the corresponding antiferromagnetic case (with J 1 = +1). The magnetic order parameter is found to behave similarly for the ferromagnetic and the antiferromagnetic models for large values of the frustration parameter J 2. However, there are considerable differences in the behavior of the order parameters for the two models for J 2 /|J 1 | 0.6. For example, the quasiclassical collinear magnetic long-range order for the antiferromagnetic model (with J 1 = +1) breaks down at J c 2 2 ≈ 0.60, whereas the "equivalent" point for the ferromagnetic model (with J 1 = −1) occurs at J c 2 ≈ 0.11. Unlike in the antiferromagnetic model (with J 1 = +1), where a plaquette valence-bond crystal phase intrudes between the two corresponding quasiclassical antiferromagnetic phases (with Néel and striped order) for J c 1 2 < J 2 < J c 2 2 , with J c 1 2 ≈ 0.47, we find no clear indications at all in the ferromagnetic model for an intermediate magnetically disordered phase between the corresponding phases exhibiting ferromagnetic and striped order. Instead the evidence for the ferromagnetic model (with J 1 = −1) points to one of two scenarios: either there is a direct first-order transition between the two magnetically ordered phases, as mentioned above; or there exists an intervening phase between them in the very narrow range 0.10 J 2 0.12, which is probably a remnant of the spiral phase that exists in the classical counterpart of the model over the larger range 1 10 < J 2 < 1 5 .
Journal of Physics: Conference Series, 2009
Using the coupled-cluster method for infinite lattices and the exact diagonalization method for finite lattices, we study the influence of an exchange anisotropy ∆ on the groundstate phase diagram of the spin-1/2 frustrated J1-J2 XXZ antiferromagnet on the square lattice. We find that increasing ∆ > 1 (i.e. an Ising type easy-axis anisotropy) as well as decreasing ∆ < 1 (i.e. an XY type easy-plane anisotropy) both lead to a monotonic shrinking of the parameter region of the magnetically disordered quantum phase. Finally, at ∆ c ≈ 1.9 this quantum phase disappears, whereas in the pure XY limit (∆ = 0) there is still a narrow region around J2 = 0.5J1 where the quantum paramagnetic ground-state phase exists.
Numerical study of the frustrated ferromagnetic spin-1/2 chain
2012
The ground state phase diagram of the frustrated ferromagnetic spin-1/2 chain is investigated using the exact diagonalization technique. It is shown that there is a jump in the spontaneous magnetization and the ground state of the system undergos to a phase transition from a ferromagnetic phase to a phase with dimer ordering between next-nearest-neighbor spins. Near the quantum transition point, the critical behavior of the ground state energy is analyzed numerically. Using a practical finite-size scaling approach, the critical exponent of the ground state energy is computed. Our numerical results are in good agreement with the results obtained by other theoretical approaches.