We implement a Chern-Simons (CS) contribution into the compact QED<Subscript>3</Subscript> description of the antiferromagnetic Heisenberg model in two dimensions at zero temperature. The CS term allows for the conservation of the SU(2) symmetry of the quantum spin system and fixes the flux through a plaquette to be a...</subscript>

The energy gap of the 1D AF-Heisenberg model in the presence of both uniform (H) and staggered (h) magnetic fields is investigated using the exact diagonalization technique. The opening of the gap in the presence of a staggered field is found to scale with h<Superscript>ν</Superscript>, where ν=ν(H) is the critical...</superscript>

We study the one-dimensional isotropic spin-1 Heisenberg magnet with antiferromagnetic nearest-neighbor (nn) and next-nearest-neighbor (nnn) interactions by using the modified spin wave theory (MSWT). The ground state energy and the singlet-triplet energy gap are obtained for several values of...

We have studied the behavior of the energy gap of the 1D AF spin-<InlineEquation ID="Equ1"> <EquationSource Format="TEX">$\frac{1}{2}$</EquationSource> </InlineEquation> XXZ model in a transverse magnetic field (h) using the exact diagonalization technique. The ground state phase diagram consists of two spin-flop and paramagnetic phases. Using a modified finite-size scaling...</equationsource></inlineequation>

We compute the magnetic susceptibility and specific heat of the spin-<InlineEquation ID="Equ2"> <EquationSource Format="TEX">$\frac{1}{2}$</EquationSource> </InlineEquation> Heisenberg model on the kagome lattice with high-temperature expansions and exact diagonalizations. We compare the results with the experimental data on ZnCu<Subscript>3</Subscript>(OH)<Subscript>6</Subscript>Cl<Subscript>2</Su bscript> obtained by Helton et al. [Phys. Rev. Lett....<//su></subscript></subscript></subscript></equationsource></inlineequation>

We study the ground-state properties of frustrated Heisenberg ferrimagnetic ladders with antiferromagnetic exchange interactions and two types of alternating sublattice spins. In the limit of strong rung couplings, we show that the mixed spin-1/2 and spin-1 ladders can be systematically mapped...

Motived by the necessity of explicit and reliable calculations, as a valid contribution to clarify the effectiveness and, possibly, the limits of the Tsallis thermostatistics, we formulate the Two-Time Green Functions Method in nonextensive quantum statistical mechanics within the optimal...

We study the low-temperature thermodynamic properties of a number of frustrated quantum antiferromagnets which support localized magnon states in the vicinity of the saturation field. For this purpose we use (1) a mapping of the low-energy degrees of freedom of spin systems onto the hard-core...

The Jordan-Wigner transformation is applied to study the ground state properties and dimerization transition in the J<Subscript>1</Subscript>-J<Subscript>2</Subscript> XXZ chain. We consider different solutions of the mean-field approximation for the transformed Hamiltonian. Ground state energy and the static structure factor are compared...</subscript></subscript>