Two-pulse, echo-detected (ED) electron paramagnetic resonance (EPR) spectroscopy was used to study the librational motions of spin-labeled lipids in membranes of dipalmitoylphosphatidylcholine + 50 mol % cholesterol. The temperature dependence, over the range 77-240 K, and the dependence on position of spin-labeling in the sn-2 chain (n=5, 7, 10, 12, and 14) of the phospholipid, were characteri...

We calculate exactly the density of magnon states of the regularly alternating spin2 XX chain with Dzyaloshinskii-Moriya interaction. The obtained result permit us to examine the stability of the chain with respect to spin-Peierls dimerization. We found that depending on the dependences of Dzyaloshinskii-Moriya interaction on distortion amplitude it may act either in favour of the dimerization ...

Two nonsymmetric search directions for semideenite programming, the XZ and ZX search directions, are proposed. They are derived from a nonsymmetric formulation of the semideenite programming problem. The XZ direction corresponds to the direct linearization of the central path equation XZ = I; while the ZX direction corresponds to ZX = I. The XZ and ZX directions are well deened if both X and Z ...

We examine dynamic quantities of a random spin-1/2 isotropic XY chain in a transverse field. The randomness is related to the sign of the nearest-neighbor exchange interaction and can be eliminated by a suitable transformation. As a result, the dynamic quantities for the random spin chain are related to the same dynamic quantities for the homogeneous spin chain. We use the available results for...

Using a new version of the density-matrix renormalization group we determine the phase diagram of a model of an antiferromagnetic Heisenberg spin chain where the spins interact with quantum phonons. A quantum phase transition from a gapless spin-fluid state to a gapped dimerized phase occurs at a nonzero value of the spin-phonon coupling. The transition is in the same universality class as that...

An interest in the theoretical study of quantum spin chains exhibiting spin–Peierls phases has incredibly grown since the discovery of the first inorganic spin–Peierls compound CuGeO3 (for a review see). Although the quantum Heisenberg model is usually used as an appropriate model to describe the spin–Peierls phase transition in the available materials some generic features can be clarified wit...

The paper presents a numerical approach for the calculation of thermodynamics and spin correlations for spin-2 XY chains. To illustrate the approach we performed exact finite-chain calculations of all time-dependent two-spin correlation functions for the spin-2 Ising chain in the transverse field. The computed correlation functions permit to evaluate the frequency-dependent susceptibilities and...

We consider the Super Yang–Mills/spin system map to construct the SU(2) spin bit model at the level of two loops in Yang–Mills perturbation theory. The model describes a spin system with chaining interaction. In the large N limit the model is shown to be reduced to the two loop planar integrable spin chain.

We have investigated the spin dynamics in the strongly correlated chain copper oxide SrCuO2 for energies up to greater, similar 0.6 eV using inelastic neutron scattering. We observe a gapless continuum of magnetic excitations, which is well described by the "Müller ansatz" for the two-spinon continuum in the S=1/2 antiferromagnetic Heisenberg spin chain. The lower boundary of the continuum exte...

Magnetization measurements of Sr14−xCaxCu24O41 with 0 ≤ x ≤ 12 in magnetic fields up to 16 T show that the low-temperature magnetic response of the CuO2 spin chains changes strongly upon Ca doping. For x = 0 quantum statistical simulations yield that the temperature and field dependence of the magnetization can be well described by an effective Heisenberg model in which the ground state configu...