Spin Excitations in Low-Dimensional Quantum Antiferromagnets (English shop)

Preview

Table of Contents, Datei (51 KB)
Extract, Datei (100 KB)

Description

In this thesis we have investigated and compared the spin excitations of several low-dimensional quantum antiferromagnets, including the one-dimensional spin-1/2 chain, the one-dimensional
spin-1 chain, the two-leg spin-1/2 ladder, the four-leg spin-1/2 ladder, the two-dimensional spin-1/2 antiferromagnet, a bilayer containing two coupled spin-1/2 planes and the two-dimensional spin-1 antiferromagnet. Besides a nearest-neighbor Heisenberg interaction the in uence of a cyclic four-spin exchange on the properties of a two-leg ladder has been considered. Furthermore, the effect of spin phonon interaction on the magnetic excitations of the two-dimensional antiferromagnets has been analyzed. For these investigations several analytical and numerical techniques have been employed. The two-dimensional antiferromagnets have been treated within interacting spin-wave theory. For the investigation of the spin-1/2 chain and the two-leg spin-1/2 ladder a fermionic representation, which is based on the Jordan-Wigner transformation, has been applied. The Density Matrix Renormalization Group (DMRG) has been used to analyze the properties of the one-dimensional spin-1 chain, the two-leg spin-1/2 ladder and the four-leg spin-1/2 ladder.