Magnon-mediated binding between holes in an antiferromagnet

The long-range forces between holes in an antiferromagnet are due to magnon exchange. The one-magnon exchange potential between two holes is proportional to cos(2 ϕ)/r ² where r is the distance vector of the holes and ϕ is the angle between r and an axis of the square crystal lattice. One-magnon exchange leads to bound states of holes with antiparallel spins resembling d-wave symmetry.     

On the possibility of the transformation of a soliton into the bound state of two excitons due to the exciton-photon interaction

This paper is concerned with the study of the probability of the soliton transformation, in the molecular chain, into the bound state of two excitons through the exciton-photon interaction.

It is established that this interaction, in general, is weak. In special cases, if the value of dynamical interaction becomes close to double the value of the resonant interaction between neighbouring molecules, the probability of the soliton transformation can be significant.     

On the possibility of self-trapping transition of acoustic polarons in two dimensions

A 2D electron-longitudinal-acoustic-phonon interaction Hamiltonian is derived and used to calculate the ground-state energy of the acoustic polarons in two dimensions. The numerical results for the ground-state energy of the acoustic polarons in two and three dimensions are obtained. The 3D results agree with those obtained by using the Feynman path-integral approach. It is found that the critical coupling constant of the transition from the quasifree state to the self-trapped state in the 2D case is much smaller than in the 3D case for a given cutoff wave-vector. The theory has been used to judge the possibility of the self-trapping for several real materials. The results indicate that the self-trappings of the electrons in AlN and the holes in AlN and GaN are expected to be observed in 2D systems.     

The two dimensional antiferromagnetic Heisenberg model in the presence of an external field

We present numerical results on the zero temperature magnetization curve and the static structure factors of the two dimensional antiferromagnetic Heisenberg model in the presence of an external field. The impact of frustration is also studied.     

On the possibility of observation of the future for movement in the field of black holes of different types

It is shown for a spherically symmetric black hole of general type that it is impossible to observe the infinite future of the Universe external to the hole during the finite proper time interval of the free fall. Quantitative evaluations of the effect of time dilatation for circular orbits around the Kerr black hole are obtained and it is shown that the effect is essential for ultrarelativistic energies of the rotating particle.     

Conductivity anisotropy in the antiferromagnetic state of iron pnictides

Recent experiments on iron pnictides have uncovered a large in-plane resistivity anisotropy with a surprising result: The system conducts better in the antiferromagnetic x direction than in the ferromagnetic y direction. We address this problem by calculating the ratio of the Drude weight along the x and y directions, D(x)/D(y), for the mean-field Q=(π,0) magnetic phase diagram of a five-band model for the undoped pnictides. We find that D(x)/D(y) ranges between 0.2相似文献   

The ground state of an antiferromagnetic superconductor in the presence of a homogeneous magnetic field

The effect of a homogeneous magnetic field, H₀. on the ground state of an antiferromagnetic superconductor has been investigated. Assuming a one-dimensional like half-filled band, we have found a new state having gapless superconductivity and H₀-dependent order parameter. This state exists for H_Q/Δ₀>0.22 and when ∣Δ ? H_Q∣?H₀ < Δ + H_Q (H_Q is the staggered magnetic field, Δ is the superconducting order parameter and Δ₀ is Δ in the absence of H_Q and H₀).     

On the possibility of revealing the transition of a baryon pair state to a six-quark confinement state

Proton-proton collisions are considered to find favourable conditions for searching for the transition of a baryon pair state to a hexa-quark confinement state (3q) + (3q) → (6q)_cnf. It is admitted that central pp collisions in a definite range of the initial energy can lead to creation of an intermediate compound system where the hexa-quark dibaryon can be formed. Criteria for selection of central collision events and for manifestation of the quark-structure dibaryon production are proposed.     

On the uniqueness of the equilibrium state for antiferromagnetic Ising spin system in the phase transition region

We show that at low temperature an Ising spin system with antiferromagnetic interaction in a small enough external magnetic field has only one translationally invariant state.     

On the possibility of quantization of the conductance in the microwave-induced resistive state of layered superconductors

It was observed that a microwave field induces constant differential resistance steps, close in magnitude to the reciprocal of the conductance quantum h/2e ², in the current-voltage characteristics (IVCs) of layered structures with an intrinsic Josephson effect under conditions of transport in a direction perpendicular to the layers. A qualitative explanation of this result is proposed. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 1, 68–71 (10 January 1998)     

Evidence for the singlet-dimer ground state in an S = 1 antiferromagnetic bond alternating chain

Susceptibility, ESR, and magnetization measurements have been performed on single crystals of an S = 1 bond alternating chain compound: [Ni(333-tet) (mu-NO2)] (ClO4) (333-tet = N,N'-bis(3-aminopropyl)propane-1,3-diamine) and the compound doped with a small amount of Zn. We observed an anomalous angular dependence in the Zn-doped sample. These results are well explained by the model based on the valence-bond solid picture for the singlet-dimer phase. The picture implies that the free spins of S = 1 with a positive uniaxial single-ion anisotropy are induced at the edges of the chains without forming the singlet dimer.     

Statistical approach to the antiferromagnetic ground state problem

The statistical approach is adopted in an attempt to find the antiferromagnetic ground state. As a result an eigenstate of the Heisenberg hamiltonian is found which is not the true ground state, but which could serve as a useful starting point for other methods.The author is grateful to ing. P. Novák for valuable discussions.     

On the possibility of an analytic solution of the three-body problem

Three-body Faddeev equations in the Noyes-Fiedeldey form are rewritten as a matrix analog of a one-dimensional nonrelativistic Schrödinger equation. Unlike the method of K-harmonics, where a similar equation was obtained by expansion of a three-body Schrödinger equation wavefunction into the orthogonal set of functions of two variables (K-harmonics), the use of the Noyes-Fiedeldey form of Faddeev equations allows us to limit ourselves to the expansion in functions of one variable only. The solutions of the above mentioned matrix equation are obtained. These solutions converge uniformly within every interval of continuity of the matrix, which corresponds to the potential of that equation. Their asymptotic behavior for large interparticle distances is discussed. The solutions for the harmonic oscillator, inverse-square, and Coulomb-Kepler potentials are found. It is shown that energy levels in the last case may be calculated from a simple formula which is very similar to the corresponding formula for the two-body Coulomb-Kepler problem. This formula can be easily generalized to the case of n particles interacting with inverse distance potentials.     

Ground state of ferromagnet with antiferromagnetic impurity

The Heisenberg ferromagnet with an antiferromagnetic impurity and arbitrary spin is considered. The method is suggested for constructing the ground state of such a system, the method using the Jacobi matrix technique. As an example, there has been investigated the ferromagnet with a simple cubic lattice and the matrix spin $\text{S =}\text{1}\text{2}$, and the impurity spin S′ = 1. The energy and wave function of the ground state are found as dependent on the system parameters.     

On the nonlinear dynamics of the easy-plane antiferromagnetic chain in an external magnetic field

We present a theoretical investigation of soliton excitations in an easy-plane 1d antiferromagnet in an external magnetic field beyond the Sine-Gordon approximation. We find that there exist two types of solitons. One of them depends strongly on the magnetic field, becoming unstable at a critical magnetic field B_c. The other one is stable for all magnetic fields and can be described by a Sine-Gordon model. We discuss the relevance of these excitations for neutron scattering experiments.     

Partially disordered antiferromagnetic state in two-dimensional triangular-lattice antiferromagnet

The partially disordered antiferromagnetic (PDA) state, as an exotic phase peculiar to the antiferromagnet with Ising spin in triangular lattice, is investigated by using Monte Carlo simulations of Wang-Landau algorithm and Glauber algorithm. It is revealed that PDA state, as the ground state of the triangular antiferromagnetic system, presents the complicated spin configuration due to geometrical frustration. The formation of multi-domain structure within the framework of honeycomb antiferromagnet results in the high degeneracy of PDA state. And this degeneracy of ground state can be lifted by a small magnetic field. Consequently the system shows the ferrimagnetic state, and the magnetization plateau of 1/3 saturate value (Ms) is observed in many experiments. Moreover, due to the multi-domain structure of PDA state and those spins on domain walls, the metastable steps may manifest themselves superposed on the 1/3Ms plateau in some special cases.