Related papers: Ground-state factorization and quantum phase trans…
We study the ground-state properties of weakly frustrated Heisenberg ferrimagnetic chains with nearest and next-nearest neighbor antiferromagnetic exchange interactions and two types of alternating sublattice spins S_1 > S_2, using 1/S…
Finite-size effects are studied in ground states of antiferromagnetic (AF) ANNNI chains in a field. It is shown that field can induce a variety of inhomogeneous states in finite chains. They are composed of two shifted AF states with the…
The magnetization curve of the $(S,s)=(1,1/2)$ ferrimagnetic alternating spin chain with the single-ion anisotropy $D$ is investigated with the numerical exact diagonalization of finite clusters and size-scaling analyses. The system has a…
We look into the quantum phase diagram of a spin-$\frac{1}{2}$ antiferromagnet on the square lattice with degenerate Shastry-Sutherland ground states, for which only a schematic phase diagram is known so far. Many exotic phases were…
We show that two-dimensional fermions with dispersion $k^2$ or $k^4$ undergo a first-order Stoner transition to a fully spin-polarized state despite that the spin susceptibility diverges at the critical point. We extend our analysis to…
We study the effects of an in-plane magnetic field on the ground state properties of both gapless and gapped graphene sheets within Random Phase Approximation. The critical magnetic field which leads to a fully spin polarized phase…
The ground state magnetization process of the S=1 antiferromagnetic chain with the easy-axis single-ion anisotropy described by negative $D$ is investigated. It is numerically found that a phase transition between two different gapless…
We have found the exact ground state for two frustrated quantum spin-1/2 models on a linear chain. The first model describes ferromagnet- antiferromagnet transition point. The singlet state at this point has double-spiral ordering. The…
A method is presented for the calculation of all exact ground states of diluted antiferromagnets and random field systems in an arbitrary range of fields. It works by calculating all jump-fields B,\Delta where the system changes it's ground…
A new variational technique for investigation of the ground state and correlation functions in 1D quantum magnets is proposed. A spin Hamiltonian is reduced to a fermionic representation by the Jordan-Wigner transformation. The ground state…
We study the phase diagram of one-dimensional quantum ferrimagnets by using a numerical exact diagonalization of a finite size system along with a field-theoretical non-linear $\sigma$ model of the quantum ferrimagnets at zero temperature…
Nonrelativistic Hamiltonians with large, even infinite, ground-state degeneracy are studied by connecting the degeneracy to the property of a Dirac operator. We then identify a special class of Hamiltonians, for which the full space of…
The ground state phase diagram of the alternating spin-1/2 chains with anisotropic ferromagnetic coupling under the influence of a symmetry breaking transverse magnetic field is studied. We have used the exact diagonalization technique. In…
We study the geometric phase of the ground state in the extended quantum compass model in presence of a transverse field. The exact solution is obtained by using the Jordan-Wigner transformation which maps the Hamiltonian on a fermionic…
We study state-sum constructions of G-equivariant spin-TQFTs and their relationship to Matrix Product States. We show that in the Neveu-Schwarz, Ramond, and twisted sectors, the states of the theory are generalized Matrix Product States. We…
The Fredkin model describes a spin-half chain segment subject to three-body, correlated-exchange interactions and twisted boundary conditions. The model is frustration-free, and its ground state wave function is known exactly. Its…
The spin-Peierls transition in the ground state of a quasi-one-dimensional spin-1/2 Heisenberg model coupled to adiabatic bond phonons is studied using a quantum Monte Carlo (QMC) method. The transition from a gapless Neel state to a…
We propose a ground-state ansatz for the Ohmic spin-boson model that improves upon the variational treatment of Silbey and Harris for biased systems in the scaling limit. In particular, it correctly captures the smooth crossover behaviour…
The spin-$1$ orthogonal dimer chain is investigated using the Density Matrix Renormalization Group (DMRG) algorithm. A transformation to a basis that uses the local eigenstates of the orthogonal dimers, while retaining the local spin states…
The mean-field triplon analysis is developed for spin-S quantum antiferromagnets with dimerized ground states. For the spin-1/2 case, it reduces to the well known bond-operator mean-field theory. It is applied to a coupled-dimer model on…