Unlike the Fourier series expansion, the discrete Fourier transform is defined on a finite
basis set of harmonic functions. The first approach is widely used in condensed matter to …

The thermodynamic properties of ferromagnetic spin chains have been analyzed with a
variety of microscopic methods over the years: Bethe ansatz, spin-wave theory, Schwinger …

The method of discrete Fourier transform (DFT) is applied to obtain the exact one-or bi-
magnonic states in several finite one-dimensional spin systems. The advantage of DFT …

We report on a qualitative change of the character of interacting magnon excitations in a
ferromagnet due to finite size. Within an improved continuum approach excitation modes are …

The thermodynamic properties of ferromagnetic spin chains have been the subject of many
publications. Still, the problem of how the spin–wave interaction manifest itself in these low …

The finite chain of singly occupied twofold degenerate orbital sites with Hund's rule coupling
is considered. The equation of motion for the combined spin and orbital excitation is solved …

We study a quantum spin-1/2 chain that is dual to the canonical problem of non-equilibrium
Kawasaki dynamics of a classical Ising chain coupled to a thermal bath. The Hamiltonian is …

It is shown that Bethe's exact solution for the finite Heisenberg ferromagnetic chain can be
obtained via a direct Fourier transform. Unlike the Bethe ansatz approach, the latter is not …

We study the nature of collective two-spin excitations in disordered S= 1∕ 2 ferromagnetic
chains. Using a direct diagonalization scheme, we characterize the two-magnon eigenstates …

Ce mémoire est composé de deux articles portant respectivement sur les chaînes de spin–
1/2 critiques quantiques d'Ising–Kawasaki et de Fredkin. La première chaîne provient d'une …