Phase diagram study of a dimerized spin-S zig?zag ladder

J. M. MATERA; C. A. LAMAS

JOURNAL OF PHYSICS CONDENSED MATTER

IOP PUBLISHING LTD

Lugar: Londres; Año: 2014 vol. 26 p. 326004 - 326004

0953-8984

The phase diagram of a frustrated spin-$S$ zig-zag ladder is studied through different  numerical and analytical methods. We show that for arbitrary $S$, there is a family of Hamiltonians for which a fully dimerized state is an  exact ground state,being the Majumdar-Ghosh point a particular member of this family.We show that the system presents a transition between a dimerized phase to a N´eel-like phase for $S=1/2$, and spiral phases can appear for large $S$.The phase diagram is characterized by means of a generalization of the usual Mean Field Approximation (MFA). The novelty in the present implementation is to consider the strongest coupled sites as the unit cell. The gap and the excitation spectrum is analyzed through the Random Phase Approximation (RPA).  Also, a perturbative treatment to obtain the critical points is discussed.  Comparisons of the  results with numerical methods like DMRG are also presented.