arXiv subjects

Karen A. Musaelian

Publications and source records attributed to Karen A. Musaelian.

2 recordsLinked to original sources

arXiv1995

Magnetic Phases of the 2D Hubbard Model at Low Doping

We study the equilibrium spin configuration of the 2D Hubbard model at low doping, when a long-range magnetic order is still present. We use the spin-density-wave formalism and examine the two suggested candidates for a ground state: the planar spiral $(π,Q)$ and $(Q,Q)$ states. In a mean-field theory, each of these two states is a ground state in a certain range of parameters. We however show that both states have negative bosonic modes in a transverse channel which implies that the spiral states are in fact unstable (the $(Q,Q)$ state, in addition, has a negative longitudinal stiffness). We searched for a ground state in a parameter range which on a mean-field level favored the $(π,Q)$ phase, and found that the equilibrium spin configuration is noncoplanar. These findings lead to a novel scenario of spin reorientation upon doping in Hubbard antiferromagnets.

cond-mat↗

arXiv1994

On the contrasting spin dynamics of $La_{2-x}Sr_xCuO_4$, $Nd_{2-x}Ce_xCuO_4$ and $YBa_2Cu_3O_{6+x}$ near half filling

We present simple calculations which show that incommensurability upon doping and the width of the magnetically ordered phase in Mott-Hubbard insulators depend strongly on the location of the hole/electron pockets in the Brillouin zone. For $LaSrCuO$ systems, we found the pockets at $(\pm π/2,\pm π/2)$, in which case the corrections to the antiferromagnetic spin stiffness grow with doping and destroy the commensurate antiferromagnetic ordering already at a very small doping. On the other hand, in $NdCeCuO$, the hole pockets are located at $(π,0)$ and the symmetry related points, in which case the corrections to the stiffness scale linearly with the density of carriers and do not destroy commensurate spin ordering. For $YBCuO$, systems the situation is less certain, but our results favor hole pockets at $(π/2,π/2)$. We also discuss briefly the tendency towards phase separation.

cond-mat↗