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A L Chernyshev

Publications and source records attributed to A L Chernyshev.

8 recordsLinked to original sources
PubMed2006

Magnon decay in noncollinear quantum antiferromagnets.

Instability of the excitation spectrum of an ordered noncollinear Heisenberg antiferromagnet with respect to spontaneous two-magnon decays is investigated. We use a spin-1/2 antiferromagnet on a triangular lattice as an example and examine the characteristic long- and short-wavelength features of its zero-temperature spectrum within the 1/S approximation. The kinematic conditions are shown to be crucial for the existence of decays and for overall properties of the spectrum. The XXZ and the J-J generalizations of the model, as well as the role of higher-order corrections, are discussed.

Journal Article↗
PubMed2005

Thermal conductivity of quasi-one-dimensional antiferromagnetic spin-chain materials.

We study heat transport in quasi-one-dimensional spin-chain systems by considering the model of one-dimensional bosonic spin excitations interacting with three-dimensional phonons and impurities in the limit of weak spin-lattice coupling and fast spin excitations. A combined effect of the phonon and impurity scatterings yields the following spin-boson thermal conductivity behavior: kappa(s) proportional to T2 at low, kappa(s) proportional to T-1 at intermediate, and kappa(s)= const at higher temperatures. Our results agree well with the existing experimental data for Sr2CuO3. We predict an unusual dependence on the impurity concentration for a number of observables and propose further experiments.

Journal Article↗
PubMed2005

Edge states in doped antiferromagnetic nanostructures.

We study competition between different phases in a strongly correlated nanostructure with an edge. Making use of the self-consistent Green's function and density matrix renormalization group methods, we study a system described by the t-J(z) and t-J models on a strip of a square lattice with a linear hole density n(||). At intermediate interaction strength J/t we find edge stripelike states, reminiscent of the bulk stripes that occur at smaller J/t. We find that stripes attach to edges more readily than hole pairs, and that the edge stripes can exhibit a peculiar phase separation.

Journal Article↗
PubMed2003

Spin diffusion in double-exchange manganites.

The theoretical study of spin diffusion in double-exchange magnets by means of dynamical mean-field theory is presented. We demonstrate that the spin-diffusion coefficient becomes independent of the Hund's coupling J(H) in the range of parameters J(H)S>>W>>T, W being the bandwidth, relevant to colossal magnetoresistive manganites in the metallic part of their phase diagram. Our study reveals a close correspondence as well as some counterintuitive differences between the results on Bethe and hypercubic lattices. Our results are in accord with neutron-scattering data and with previous theoretical work for high temperatures.

Journal Article↗
PubMed2001

Long-range order and low-energy spectrum of diluted 2D quantum antiferromagnet.

The problem of a diluted two-dimensional quantum antiferromagnet on a square lattice is studied using spin-wave theory. The influence of impurities on static and dynamic properties is investigated and a good agreement with experiments and Monte Carlo data is found. The hydrodynamic description of spin waves breaks down at characteristic wavelengths Lambda greater than exp(const/x), x being an impurity concentration, while the order parameter is free from anomalies. We argue that this dichotomy originates from strong scattering of the low-energy excitations in two dimensions.

Journal Article↗
PubMed1991

[State of the pancreas in persons with alcohol-related risk factors].

Clinico-laboratory and instrumental techniques were used to investigate the pancreas states in alcohol abusers at preclinical stage. Examined were 74 persons, 24-31 years of age, with established alcohol-related risk-factors, who would consider themselves healthy. The character and forms of alcohol addiction were determined by a psychiatrist. Complaints were studied in the group which fell into astheno-vegetative syndrome (56.2%), dyspeptic disorders (32%) and pain (14.1%). Ultrasound scanning of all the cases was performed. Pancreas tissue echostructure changes were detected in 16% cases, including fibrosis and edema in 7 and 5 cases, respectively. Hydrochloride methionine intraduodenal testing was performed to assess the pancreas external secretion indices. 98.6% cases manifested changes in external secretory function, e.i. increased concentration and secretion of amylase, decreased concentration and secretion of bicarbonates in the stable volume and rate of pancreatic juice secretion.

Adult↗