Valeri N. Kotov

Learn More
We examine the conditions necessary for the presence of localized magnetic moments on adatoms with inner shell electrons in graphene. We show that the low density of states at the Dirac point, and the anomalous broadening of the adatom electronic level, lead to the formation of magnetic moments for arbitrarily small local charging energy. As a result, we(More)
The main feature in the elastic neutron scattering of La2-xSrxCuO4 is the existence of incommensurate peaks with positions that jump from 45 degrees to 0 degrees at 5% doping. We show that the spiral state of the t-t(')-t('')-J model with realistic parameters describes these data perfectly. We explain why in the insulator the peak is at 45 degrees while it(More)
We calculate exactly the vacuum polarization charge density in the field of a subcritical Coulomb impurity, Z|e|/r, in graphene. Our analysis is based on the exact electron Green's function, obtained by using the operator method, and leads to results that are exact in the parameter Zalpha, where alpha is the "fine-structure constant" of graphene. Taking(More)
We consider the quantum phase transition between a Néel antiferromagnet and a valence-bond solid (VBS) in a two-dimensional system of S = 1/2 spins. Assuming that the excitations of the critical ground state are linearly dispersing deconfined spinons obeying Bose statistics, we derive expressions for the specific heat C and the magnetic susceptibility χ at(More)
We study the excitation spectrum and ground state properties of the two-leg S = 1 2 quantum spin ladder with staggered dimerization. Two massive phases, separated by a critical line are found, as predicted by previous analysis , based on the non-linear sigma model (NLSM). We have used dimer series expansions, exact diagonalization of small clusters and(More)
The magnetization, M(H< or =30 T,0.7< or =T< or =300 K), of (C5H12N)2CuBr4 has been used to identify this system as an S = 1/2 Heisenberg two-leg ladder in the strong-coupling limit, J( perpendicular) = 13.3 K and J( parallel) = 3.8 K, with H(c1) = 6.6 T and H(c2) = 14.6 T. An inflection point in M(H,T = 0.7 K) at half saturation, M(s)/2, is described by an(More)
We discuss the spiral spin density wave model and its application to explain properties of underdoped La 2−x Sr x CuO 4. We argue that the spiral picture is theoretically well justified in the context of the extended t − J model, and then show that it can explain a number of observed features, such as the location and symmetry of the incommensurate peaks in(More)
frustration: elementary quasiparticles and many-particle bound states. Abstract The excitation spectrum of the two-chain S = 1/2 Heisenberg spin ladder with additional second neighbor frustrating interactions is studied by a variety of techniques. A description, based on a mapping of the model onto a Bose gas of hard-core triplets is used to determine the(More)
We study a Heisenberg S=1/2 ring-exchange antiferromagnet which exhibits a quantum phase transition from a spontaneously dimerized (valence bond solid) phase to a magnetically ordered (Néel) phase. We argue that the quantum transition is of uncon-ventional nature; both singlet and triplet modes of high density condense as the transition is approached from(More)