6 papers
Effects of biquadratic exchange on the spectrum of elementary excitations in spin ladders
S. Brehmer, H. -J. Mikeska, M. Mueller +2
We investigate the influence of biquadratic exchange interactions on the low-lying excitations of a S=1/2-ladder using perturbation theory, numerical diagonalization of finite syst…
Thermodynamics of the (1,1/2) Ferrimagnet in Finite Magnetic Fields
K. Maisinger, U. Schollwoeck, S. Brehmer +2
We investigate the specific heat and magnetisation of a ferrimagnet with gS=1 and S=1/2 spins in a finite magnetic field using the transfer matrix DMRG down to T=0.025J. Ferromagne…
Elementary Excitations of Heisenberg Ferrimagnetic Spin Chains
Shoji Yamamoto, S. Brehmer, H. -J. Mikeska
We numerically investigate elementary excitations of the Heisenberg alternating-spin chains with two kinds of spins 1 and 1/2 antiferromagnetically coupled to each other. Employing…
Elementary excitations in the gapped phase of a frustrated S=1/2 spin ladder: from spinons to the Haldane triplet
S. Brehmer, A. K. Kolezhuk, H. -J. Mikeska +1
We use the variational matrix-product ansatz to study elementary excitations in the S=1/2 ladder with additional diagonal coupling, equivalent to a single S=1/2 chain with alternat…
Low Temperature Properties of Quantum Antiferromagnetic Chains with Alternating Spins S=1 and 1/2
S. Brehmer, H. -J. Mikeska, S. Yamamoto
We study the low-temperature properties of S=1 and 1/2 alternating spin chains with antiferromagnetic nearest-neighbor exchange couplings using analytical techniques as well as a q…
Phase diagram and hidden order for generalized spin ladders
S. Brehmer, H. -J. Mikeska, U. Neugebauer
We investigate the phase diagram of antiferromagnetic spin ladders with additional exchange interactions on diagonal bonds by variational and numerical methods. These generalized s…