arXiv subjects
Publications and source records attributed to D. N. Aristov.
Dzyaloshinskii-Moriya (DM) interaction in the paramagnetic state leads to the incommensurate spin fluctuations with incommensurate vector proportional to the relative strength of the DM interaction. We show that the DM interaction leads to helical spin fluctuations which may be observed by the polarized neutron scattering.
We discuss the influence of the Dzyaloshinskii-Moriya (DM) interaction in the Heizenberg spin chain model for the observables in the polarized neutron scattering experiments. We show that different choices of the parameters of DM interaction may leave the spectrum of the problem unchanged, while the observable spin-spin correlation functions may differ qualitatively. Particularly, for the uniform DM interaction one has the incommensurate fluctuations and polarization-dependent neutron scattering in the paramagnetic phase. We sketch the possible generalization of our treatment to higher dimensions.
The indirect RKKY interaction in a layered metal with nearly nested (almost squared) Fermi surface is evaluated analytically. The final expressions are obtained in closed form as a combination of Bessel functions. We show that the expected ``2k_F'' oscillations occur as the far asymptote of our expressions, where a value of the effective Fermi momentum k_F depends on the direction in r-space. We demonstrate the existence of the intermediate asymptote of the interaction which is of the sign-reversal antiferromagnetic type. This part of RKKY interaction is the only term surviving in the limit of exact nesting. A good accordance of our analytical formulas with numerical findings is found until the interatomic distances.
The Landau quantization for the electron gas on a surface of sphere is considered. We show that in the regime of strong fields the lowest energy states are those with magnetic quantum numbers m of order of Phi/Phi_0, the number of magnetic flux quanta piercing the sphere. For the electron gas of low density (semiconducting situation), it leads to the formation of the electronic stripe on the equator of the sphere in high fields.
We consider the correlation functions in a gas of electrons moving within a thin layer on the surface of nanosize sphere. A closed form of expressions for the RKKY indirect exchange, superconducting Cooper loop and `density-density' correlation function is obtained. The systematic comparison with planar results is made, the effects of spherical geometry are outlined. The quantum coherence of electrons leads to the enhancement of all correlations for the points--antipodes on the sphere. This effect is lost when the radius of the sphere exceeds the temperature coherence length.
We consider the electron gas moving on the surface of a sphere in a uniform magnetic field. An exact solution of the problem is found in terms of oblate spheroidal functions, depending on the parameter $p= Φ/Φ_0$, the number of flux quanta piercing the sphere. The regimes of weak and strong fields are discussed, the Green's functions are found for both limiting cases in the closed form. In the weak fields the magnetic susceptibility reveals a set of jumps at half-integer $p$. The strong field regime is characterized by the formation of Landau levels and localization of the electron states near the poles of the sphere defined by a direction of the field. The effects of coherence within the sphere are lost when its radius exceeds the mean-free path.
We consider the static anomalous Cooper loop for the electron gas of arbitrary spatial dimensionality, D. This object enters the mean-field equation for the superconducting temperature, T_c. The closed expression in r- space is found at T=0 as an analytical function of D. Its counterpart in q-space has a logarithmic singularity at q=0 and no singularities at q=2k_F for any D. We extend our analysis for the case of finite T and note that in two dimensions the bound state of two electrons is possible even in the limit k_F -> 0. We comment on the possible implications of this fact for the theory of high-T_c cuprates.
We analyze the asymptotic behavior of the exponential form in the fermionic density operators as the function of ruling parameter Q. In the particular case Q=πthis exponential associates with the Wigner-Jordan transformation for XY spin chain model. We compare the bosonization approach and the evaluation via the Toeplitz determinant. The use of Szego-Kac theorem suggests that at Q>π/3 the divergent series for intrinsic logarithm provides a bosonized solution and faster decaying one, found as the logarithm's value on another sheet of the complex plane. The second solution is revealed as umklapp-process on the fictitious lattice while originates from backscattering terms in bosonized density. Our finding preserves in a wide range of fermion filling ratios.
We present the results of analytical evaluation of the indirect RKKY interaction in a layered metal with nearly nested (almost squared) Fermi surface. The final expressions are obtained in closed form as a combination of Bessel functions. We discuss the notion of the ``2k_F'' oscillations and show that they occur as the far asymptote of our expressions. We show the existence of the intermediate asymptote of the interaction which is of the sign-reversal antiferromagnetic type and is the only term surviving in the limit of exact nesting. A good accordance of our analytical formulas with numerical findings is demonstrated until the interatomic distances. The obtained expressions for the Green's functions extend the previous analytical results into the region of intermediate distances as well.
We study the spin fluctuation of the oxygen deficient planes of YBa(2)Cu(3)O(6+x). The Cu-O chains that constitute these planes are described by a model that includes antiferromagnetic interactions between spins and Kondo-like scattering of oxygen holes. The spectrum of magnetic excitations shows the presence of incommensurate dynamic fluctuations along the direction of the chains. The presence of itinerant holes is responsible for the existence of important differences between the spin dynamics of this system and that of a quasi-one-dimensional localized antiferromagnet. We comment on the possibility of experimental observation of these fluctuations.
In a recent Letter Balatsky and Salkola made their conclusion about the absence of localization in disordered d-wave superconductors exploiting the idea that strongly overlapping impurity states formed a network capable to provide the transport. We present here the correct estimate of hopping matrix elements between two impurities which were the basic quantities for the subsequent consideration in the abovementioned Letter. We conclude, that the picture of the impurity-impurity potential acting only within the slowly broadening tails claimed by Balatsky and Salkola as well as all the physical consequences of this picture appear to be incorrect.
We present an analytical method which enables one to find the exact spatial dependence of the indirect RKKY interaction between the localized moments via the conduction electrons for the arbitrary dimensionality $n$. The corresponding momentum dependence of the Lindhard function is exactly found for any $n$ as well. Demonstrating the capability of the method we find the RKKY interaction in a system of metallic layers weakly hybridized to each other. Along with usual $2k_F$ in-plane oscillations the RKKY interaction has the sign-reversal character in a direction perpendicular to layers, thus favoring the antiferromagnetic type of layers' stacking.
The RKKY interaction between rare-earth (RE) ions in high-$T_c$ superconductors is considered at $T\ll T_c$. It is shown that this interaction consists of two terms: conventional oscillating one and the positive term, which is proportional to the gap function and decreases in the $2D$ case inversely proportional to the distance. In the antiferromagnetic state of the RE subsystem this positive interaction gives rise for frustrations which diminishes the Neel temperature. In the case of strongly anisotropic gap function this frustration produces two different values of the effective nearest neighbor exchange coupling between RE ions along the $a$ and $b$. This anisotropy has been established experimentally in Ref.\cite{6,7,8}.
We calculate the damping of excitations due to four-fermionic interaction in the case of two-dimensional superconductor with nodes in the spectrum. At zero temperature and low frequencies it reveals gapless $ω^3$ behavior at the nodal points. With the frequency increasing the crossover to the normal-state regimes appears. At high frequencies the damping strongly depends on details of a normal-state spectrum parametrization. Two important particular cases such as the models of almost free and tight-binding electrons are studied explicitly and the characteristic scales are expressed through the model-free parameters of the spectrum at the nodal points. The possibility of crossover in temperature dependence of damping in the superconducting phase is discussed.
We examine the NMR experimental data for the normal state of YBa$_2$Cu$_3$O$_{7-δ}$ within the Fermi-liquid approach. We show that the observed temperature dependence of the Knight shift and $^{17}$O ($^{89}$Y) relaxation rate in ``underdoped'' ( $T_c=60\,$K ) compound can be interpreted as resulting from a peak in the density of states near the Fermi level. The possible origin of such peak is the quasi-one-dimensional van Hove singularity in the fermionic spectrum, conjectured by Abrikosov, Gofron and Campuzano. The proposed spectrum allows us to account for the qualitatively different NMR data for ``underdoped'' and ``overdoped''( $T_c=90\,$K ) compounds by varying the value of chemical potential only.