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.Comment: 2 figure

Dynamic probes of quantum spin chains with the Dzyaloshinskii-Moriya interaction

We consider the spin-1/2 anisotropic XY chain in a transverse (z) field with the Dzyaloshinskii-Moriya interaction directed along z-axis in spin space to examine the effect of the Dzyaloshinskii-Moriya interaction on the zz, xx and yy dynamic structure factors. Using the Jordan-Wigner fermionization approach we analytically calculate the dynamic transverse spin structure factor. It is governed by a two-fermion excitation continuum. We analyze the effect of the Dzyaloshinskii-Moriya interaction on the two-fermion excitation continuum. Other dynamic structure factors which are governed by many-fermion excitations are calculated numerically. We discuss how the Dzyaloshinskii-Moriya interaction manifests itself in the dynamic properties of the quantum spin chain at various fields and temperatures

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.Comment: 11 pages, latex, 4 figure

Regularly alternating spin-1/2 anisotropic XY chains: The ground-state and thermodynamic properties

Using the Jordan-Wigner transformation and continued fractions we calculate rigorously the thermodynamic quantities for the spin-1/2 transverse Ising chain with periodically varying intersite interactions and/or on-site fields. We consider in detail the properties of the chains having a period of the transverse field modulation equal to 3. The regularly alternating transverse Ising chain exhibits several quantum phase transition points, where the number of transition points for a given period of alternation strongly depends on the specific set of the Hamiltonian parameters. The critical behavior in most cases is the same as for the uniform chain. However, for certain sets of the Hamiltonian parameters the critical behavior may be changed and weak singularities in the ground-state quantities appear. Due to the regular alternation of the Hamiltonian parameters the transverse Ising chain may exhibit plateau-like steps in the zero-temperature dependence of the transverse magnetization vs. transverse field and many-peak temperature profiles of the specific heat. We compare the ground-state properties of regularly alternating transverse Ising and transverse XX chains and of regularly alternating quantum and classical chains. Making use of the corresponding unitary transformations we extend the elaborated approach to the study of thermodynamics of regularly alternating spin-1/2 anisotropic XY chains without field. We use the exact expression for the ground-state energy of such a chain of period 2 to discuss how the exchange interaction anisotropy destroys the spin-Peierls dimerized phase

Dynamic properties of the spin-1/2 XY chain with three-site interactions

We consider a spin-1/2 XY chain in a transverse (z) field with multi-site interactions. The additional terms introduced into the Hamiltonian involve products of spin components related to three adjacent sites. A Jordan-Wigner transformation leads to a simple bilinear Fermi form for the resulting Hamiltonian and hence the spin model admits a rigorous analysis. We point out the close relationships between several variants of the model which were discussed separately in previous studies. The ground-state phases (ferromagnet and two kinds of spin liquid) of the model are reflected in the dynamic structure factors of the spin chains, which are the main focus in this study. First we consider the zz dynamic structure factor reporting for this quantity a closed-form expression and analyzing the properties of the two-fermion (particle-hole) excitation continuum which governs the dynamics of transverse spin component fluctuations and of some other local operator fluctuations. Then we examine the xx dynamic structure factor which is governed by many-fermion excitations, reporting both analytical and numerical results. We discuss some easily recognized features of the dynamic structure factors which are signatures for the presence of the three-site interactions.Comment: 28 pages, 10 fugure

Spin-Peierls instability in a quantum spin chain with Dzyaloshinskii-Moriya interaction

We analysed the ground state energy of some dimerized spin-1/2 transverse XX and Heisenberg chains with Dzyaloshinskii-Moriya (DM) interaction to study the influence of the latter interaction on the spin-Peierls instability. We found that DM interaction may act either in favour of the dimerization or against it. The actual result depends on the dependence of DM interaction on the distortion amplitude in comparison with such dependence for the isotropic exchange interaction.Comment: 12 pages, latex, 3 figure

A microscopic theory of photonucleation: Density functional approach to the properties of a fluid of two-level atoms, a part of which is excited

We use the density functional method to examine the properties of the nonuniform (two-phase) fluid of twolevel atoms, a part of which is excited. From the analysis of the equation of state of a gas of two-level atoms, a part of which is excited, the following density functional of the grand thermodynamical potential emerges width (here ΩCS[ρ(r)] is the Carnahan-Starling term, σ is the atom radius, v = 4/3πσ³, c₁ is the concentration of excited atoms, c₀ + c₁ = 1, E₁ − E₀ is the excitation energy and a is the dimensionless parameter which characterizes the atom). We use this expresМи використовуємо метод функцiоналу густини для дослiдження властивостей неоднорiдного (двофазного) плину дворiвневих атомiв, частина з яких збуджена. На основi аналiзу рiвняння стану газу дворiвневих атомiв, частина з яких збуджена, виникає наступний функцiонал густини великого термодинамiчного потенцiалу, (тут ΩCS[ρ(r)] – доданок Карнагана-Старлiнга, σ – радiус атома, v = 4/3πσ³, c₁ – концентрацiя збуджених атомiв, c₀ + c₁ = 1, E₁ − E₀ – енергiя збудження i a – безрозмiрний параметр, який характеризує атом). Ми використовуємо цей вираз для обчислення нуклеацiйного бар’єру для фазового переходу пари в рiдину за наявностi збуджених атомiв