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Wednesday, October 21, 2009
2:00 PM - 3:00 PM
CNLS Conference Room (TA-3, Bldg 1690)

Student Seminar

Local theory of magnetization plateaux in the Shastry-Sutherland Model

Leonid Isaev
Indiana University

The emergence of magnetization plateaux in two-dimensional frustrated spin systems on the Shastry-Sutherland lattice, such as the orthogonal dimer compound SrCu2(BO3)2, has puzzled physicists for more than two decades and, despite substantial advances in this field, the origin of the plateaux still remains a mystery. Theoretically there exist two major schools of thought. While both agree that plateaux correspond to crystal phases of the system, the underlying physical mechanism is being actively debated. The first camp advocates subtle non-local (in the spins) correlations, which stabilize the spin structures inside plateaux. An alternative approach assumes the short-range correlations in the ground state, and that the magnetization process can be described in terms of polarized dimers (triplons), which propagate in the background of singlet dimers. These two predictions, therefore, should be easily distinguishable experimentally.

In this talk I will present our recent achievements, which support the local picture. Our conclusions rely on the newly developed mean-field approach for studying strongly correlated systems. After briefly reviewing the methodology, I will address the nature of the robust magnetic states within plateux. In particular, I will show that a plateau is stabilized in a certain spin pattern, satisfying local commensurability conditions derived from our formalism. Our results are in agreement with recent NMR experiments on SrCu2(BO3)2. L. Isaev1, G. Ortiz1, and J. Dukelsky2 1Department of Physics, Indiana University, Bloomington IN 47405, USA 2Instituto de Estructura de la Materia - CSIC, Serrano 123, 28006 Madrid, Spain

Host: Cristian Batista