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Oleg Derzhko

Publications and source records attributed to Oleg Derzhko.

85 records · Page 5Linked to original sources
arXiv2000

The ground state properties of the spin-1/2 transverse Ising chain with periodically varying bonds and fields

Using continued fractions we study the ground state properties of the spin-1/2 Ising chain in a transverse field with periodically varying interaction strengths and external fields. We consider in detail the chain having the period of modulation of interactions equals 2 and compare the results obtained with those corresponding to the spin-1/2 isotropic XY chain in a transverse field. In contrast to the behaviour of the transverse XY chain, the transverse Ising chain does not exhibit a step-like magnetization vs. field dependence caused by the alternation of bonds, its susceptibility exhibits a logarithmic singularity at the field determined by interaction strengths, and it is stable with respect to spin-Peierls dimerization.

cond-mat↗
arXiv2000

Local magnetic properties of periodic nonuniform spin-1/2 XX chains

Using the Jordan-Wigner fermionization, Green function approach and continued fractions we examine rigorously the local magnetizations and the local static susceptibilities of the spin-1/2 XX chain in a transverse field with regularly varying exchange interactions. We discuss our findings from a viewpoint of the strong-coupling approach.

cond-mat↗
arXiv2000

Magnetization processes in quantum spin chains with regularly alternating intersite interactions

We consider the dependence magnetization vs. field at zero temperature for the spin-1/2 chains in which the intersite interactions regularly vary from site to site with a period p. In the limiting case when the smallest value of the intersite interactions tends to zero the chain splits into noninteracting identical fragments of p sites and the dependence magnetization vs. field can be examined rigorously. We demonstrate explicitly the appearance of plateaus in such dependence and discuss a presence of the magnetization values m predicted by the condition p(1/2-m)=integer [1]. We comment on the influence of the anisotropy in the interspin interaction on the magnetization profiles. Finally, we show how the case of nonzero smallest value of the intersite interactions can be considered.

cond-mat↗
arXiv2000

Thermodynamic properties of the periodic nonuniform spin-1/2 isotropic XY chains in a transverse field

Using the Jordan-Wigner transformation and the continued-fraction method we calculate exactly the density of states and thermodynamic quantities of the periodic nonuniform spin-1/2 isotropic XY chain in a transverse field. We discuss in detail the changes in the behaviour of the thermodynamic quantities caused by regular nonuniformity. The exact consideration of thermodynamics is extended including a random Lorentzian transverse field. The presented results are used to study the Peierls instability in a quantum spin chain. In particular, we examine the influence of a non-random/random field on the spin-Peierls instability with respect to dimerization.

cond-mat↗
arXiv1999

The spin-1/2 transverse XX chain with regularly alternating bonds and fields

We use continued fractions for a study of the thermodynamic properties of the periodic nonuniform spin-1/2 isotropic XY chain in a non-random/random (Lorentzian) transverse field. The obtained results permit to examine the influence of a magnetic field and randomness on the spin-Peierls dimerization.

cond-mat↗
arXiv1998

Dynamics of transverse correlations in the spin-1/2 isotropic XY chain with a correlated Lorentzian disorder

Using a numerical approach we examine the dynamics of $zz$ correlations for the spin-$1\over2$ isotropic XY chain with random Lorentzian intersite coupling and transverse field at sites that depends linearly on the neighbouring couplings. We study in detail the wave vector- and frequency-dependent $zz$ structure factor at different values of Hamiltonian parameters and temperature. We discuss the changes in the frequency profiles of the $zz$ dynamic structure factor caused by the introduced correlated disorder.

cond-mat↗
arXiv1998

Thermodynamic properties of spin-1/2 transverse XY chain with Dzyaloshinskii-Moriya interaction: Exact solution for correlated Lorentzian disorder

We extend the consideration of the spin-1/2 transverse XY chain with correlated Lorentzian disorder (Phys. Rev. B {\bf 55,} 14298 (1997)) for the case of additional Dzyaloshinskii-Moriya interspin interaction. It is shown how the averaged density of states can be calculated exactly. Results are presented for the density of states and the transverse magnetization.

cond-mat↗
arXiv1998

Initial static susceptibilities of nonuniform and random Ising chains

Within the conventional framework of standard linear response theory we have derived exact results for the initial static susceptibilities of nonuniform spin-1/2 Ising chains. The results obtained permit one to study regularly alternating-bond and random-bond Ising chains. The influence of several types of nonuniformity and disorder on the temperature dependence of the initial longitudinal and transverse static susceptibilities is discussed.

cond-mat.stat-mech↗
arXiv1998

Dynamic properties of spin-1/2 XY chains

We have considered a numerical scheme for the calculation of the equilibrium properties of spin-1/2 XY chains. Within its frames it is necessary to solve in the last resort only the 2N\times 2N eigenvalue and eigenvector problem but not the 2^N\times 2^N one as for an arbitrary system consisting of N spins 1/2. To illustrate the approach we have presented some new results. Namely, the xx dynamic structure factor for the Ising model in transverse field, the density of states for the isotropic chain with random intersite couplings and transverse fields that linearly depend on the surrounding couplings, and the zz dynamic structure factor for the Ising model in random transverse field. The results obtained are hopped to be useful for an interpretation of observable data for one-dimensional spin-1/2 XY substances.

cond-mat.stat-mech↗
arXiv1997

One variation on Lloyd's theme

One random spin-1/2 XY chain that after Jordan-Wigner fermionization reduces to the extended Lloyd's model is considered. The random-averaged one-fermion Green functions have been calculated exactly that yields thermodynamics of the spin model.

cond-mat.stat-mech↗