相关论文: Validity of spin wave theory for the quantum Heise…
We consider the quantum ferromagnetic Heisenberg model in three dimensions, for all spins $S\geq 1/2$. We rigorously prove the validity of the spin-wave approximation for the excitation spectrum, at the level of the first non-trivial…
In the last decade it has been proven that the standard spin wave theory was able to provide accurate zero-temperature results for a number of low-dimensional Heisenberg spin systems. In this chapter we introduce the main ingredients of the…
We consider the spin-S ferromagnetic Heisenberg model in three dimensions, in the absence of an external field. Spin wave theory suggests that in a suitable temperature regime the system behaves effectively as a system of non-interacting…
We study the low temperature thermodynamics of the quantum Heisenberg ferromagnet in three dimension for any value of the spin $ S \geq 1/2 $. We report on a rigorous proof of the validity of the spin-wave approximation for the excitation…
The low-temperature free energy of the spin S quantum Heisenberg ferromagnetic chain in a strong magnetic field is obtained in a two-particle approximation by using exact solution of two-spin-wave problem. The result is beyond the…
Spin-wave perturbation theory for the Heisenberg antiferromagnet at zero temperature is used to compute the finite-lattice corrections to the ground state energy, the staggered magnetization and the energy gap. The dispersion relation, the…
The thermodynamics of the quantum Heisenberg antiferromagnet on a square lattice is revisited through a linearized spin-wave theory which is well defined at any finite temperature. We re-examine in details the temperature dependence of the…
We derive the low-temperature properties of spin-S quantum Heisenberg magnets from the Gibbs free energy G(M) for fixed order parameter M. Assuming that the low-lying elementary excitations of the system are renormalized spin waves, we show…
Within the Dyson-Maleev boson formalism, we study the zero-temperature magnon dispersions in a family of one-dimensional quantum Heisenberg ferrimagnets composed of two different spins $(S_1,S_2)$ in the elementary cell. It is shown that…
We consider the ferromagnetic quantum Heisenberg model in one dimension, for any spin $S\geq 1/2$. We give upper and lower bounds on the free energy, proving that at low temperature it is asymptotically equal to the one of an ideal Bose gas…
Analytical calculations based on finite-size spin-wave theory and Monte Carlo (MC) simulations are performed to investigate the validity of the well-known relation m(H,T)=M(H,T)B_D[M(H,T)NH/T] between the induced magnetization m of the…
We calculate the effect of spin waves on the properties of finite size spin chains with a chiral spin ground state observed on bi-atomic Fe chains deposited on Iridium(001). The system is described with a Heisenberg model supplemented with…
We study quantum spin-1/2 Heisenberg ferromagnetic chains with dilute, random antiferromagnetic impurity bonds with modified spin-wave theory. By describing thermal excitations in the language of spin waves, we successfully observe a…
A perturbation spin-wave theory for the quantum Heisenberg antiferromagnets on a square lattice is proposed to calculate the uniform static magnetic susceptibility at finite temperatures, where a divergence in the previous theories due to…
We present a finite size spin wave calculation on the Heisenberg antiferromagnet on the triangular lattice focusing in particular on the low-energy part of the excitation spectrum. For s=1/2 the good agreement with the exact diagonalization…
Large scale computer simulations are used to elucidate a longstanding controversy regarding the existence, or otherwise, of spin waves in paramagnetic BCC iron. Spin dynamics simulations of the dynamic structure factor of a Heisenberg model…
Modifying the conventional spin-wave theory in a novel manner based on the Wick decomposition, we present an elaborate thermodynamics of square-lattice quantum antiferromagnets. Our scheme is no longer accompanied by the notorious problem…
A modified spin-wave theory is developed and applied to low-dimensional quantum magnets. Double-peaked specific heat for one-dimensional ferrimagnets, nuclear spin-lattice relaxation in ferrimagnetic chains and clusters, and thermal…
The Quantum Heisenberg Ferromagnet can be naturally reformulated in terms of interacting bosons (called spin waves or magnons) as an expansion in the inverse spin size. We calculate the first order interaction correction to the free energy,…
Starting from the hamiltonian for the Heisenberg ferromagnet which comprise randomly distributed nonmagnetic ions as impurities in a Bravais lattice, we express the spin operators by means of the Dyson-Maleev transformation in terms of the…