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S V Isakov

Publications and source records attributed to S V Isakov.

8 recordsLinked to original sources
PubMed2006

Spin-liquid phase in a spin-1/2 quantum magnet on the kagome lattice.

We study a model of hard-core bosons with short-range repulsive interactions at half filling on the kagome lattice. Using quantum Monte Carlo numerics, we find that this model shows a continuous superfluid-insulator quantum phase transition, with exponents z=1 and nu approximately 0.67(5). The insulator, I*, exhibits short-ranged density and bond correlations, topological order, and exponentially decaying spatial vison correlations, all of which point to a Z2 fractionalized phase. We estimate the vison gap in I* from the temperature dependence of the energy. Our results, together with the equivalence between hard-core bosons and S=1/2 spins, provide compelling evidence for a spin-liquid phase in an easy-axis spin-1/2 model with no special conservation laws.

Journal Article↗
PubMed2006

Hard-core bosons on the kagome lattice: valence-bond solids and their quantum melting.

Using large scale quantum Monte Carlo simulations and dual vortex theory, we analyze the ground state phase diagram of hard-core bosons on the kagome lattice with nearest-neighbor repulsion. In contrast with the case of a triangular lattice, no supersolid emerges for strong interactions. While a uniform superfluid prevails at half filling, two novel solid phases emerge at densities rho=1/3 and rho=2/3. These solids exhibit an only partial ordering of the bosonic density, allowing for local resonances on a subset of hexagons of the kagome lattice. We provide evidence for a weakly first-order phase transition at the quantum melting point between these solid phases and the superfluid.

Journal Article↗
PubMed2005

Why spin ice obeys the ice rules.

The low-temperature entropy of the spin ice compounds, such as and , is well described by the nearest-neighbor antiferromagnetic Ising model on the pyrochlore lattice, i.e., by the "ice rules." This is surprising since the dominant coupling between the spins is their long ranged dipole interaction. We show that this phenomenon can be understood rather elegantly: one can construct a model dipole interaction, by adding terms of shorter range, which yields precisely the same ground states, and hence entropy, as the nearest-neighbor interaction. A treatment of the small difference between the model and true dipole interactions reproduces the numerical work by Gingras et al. in detail. We are also led to a more general concept of projective equivalence between interactions.

Journal Article↗
PubMed2004

Dipolar spin correlations in classical pyrochlore magnets.

We study spin correlations for the highly frustrated classical pyrochlore lattice antiferromagnets with O(N) symmetry in the limit T-->0. We conjecture that a local constraint obeyed by the extensively degenerate ground states dictates a dipolar form for the asymptotic spin correlations, at all N not equal 2 for which the system is paramagnetic down to T=0. We verify this conjecture in the cases N=1 and N=3 by simulations and to all orders in the 1/N expansion about the solvable N=infinity limit. Remarkably, the N=infinity formulas are an excellent fit, at all distances, to the correlators at N=3 and even at N=1. Thus we obtain a simple analytical expression also for the correlations of the equivalent models of spin ice and cubic water ice, Ic.

Journal Article↗
PubMed1991

[Individual prognosis of chronic B-lymphoid leukemia course].

The characteristics of T- and B-lymphocyte content in chronic B-lymphoid leukemia (B-ChLL) patients with progressing and stable variants of the disease course, and the possibilities of their use for the individual prognosis of the course were studied. A total of 28 patients with stable and 35 patients with progressing variants of B-ChLL were investigated. T-(total and active) and B-lymphocytes were assayed in the spontaneous rosette-formation test. The individual prognosing of stable and progressing variants of B-ChLL course is possible basing on integral evaluation of total and active T-lymphocytes and B-lymphocytes with receptors to mouse red blood cells in two-dimensional parameter systems with counting the summary prognostic coefficient.

Female↗
PubMed1989

[Immunoregulating effect of prostaglandins on the course of chronic lympholeukemia].

A study was made of the effect of exogenous prostaglandins E1, E2 and E2 alpha on the proliferative response of lymphocytes in blast transformation with PHA according to the changes in permeability for 3H-thymidine, 3H-thymidine incorporation into DNA, 3H-uridine into RNA and 3H-leucine into protein in 7 patients with stable and in 17 patients with progressive B-chronic lymphoid leukemia (B-CLL). The progression of B-CLL was marked by the lack of the regulating effect of PG on lymphocytes. In stable lymphoid leukemia, an inhibitory action of PG on lymphocyte proliferation could be seen. The characteristics of the lymphocyte responses in patients with B-CLL were employed for individual prediction of the disease course.

Adjuvants, Immunologic↗