The Heisenberg antiferromagnet on the square-kagome lattice
J. Richter1 , J. Schulenburg2 , P. Tomczak3 , D. Schmalfuss1
1 Institut für Theoretische Physik, Universität Magdeburg, P.O. Box 4120, D-39016 Magdeburg, Germany
2 Universitätsrechenzentrum, Universität Magdeburg, P.O. Box 4120, D-39016 Magdeburg, Germany
3 Physics Department, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland
Condensed Matter Physics, vol. 12, No. 3, p. 507 (2009)
We discuss the ground state, the low-lying excitations as well as high-field thermodynamics of the Heisenberg antiferromagnet on the two-dimensional square-kagomé lattice. This magnetic system belongs to the class of highly frustrated spin systems with an infinite non-trivial degeneracy of the classical ground state as it is also known for the Heisenberg antiferromagnet on the kagomé and on the star lattice. The quantum ground state of the spin-half system is a quantum paramagnet with a finite spin gap and with a large number of non-magnetic excitations within this gap. We also discuss the magnetization versus field curve that shows a plateaux as well as a macroscopic magnetization jump to saturation due to independent localized magnon states. These localized states are highly degenerate and lead to interesting features in the low-temperature thermodynamics at high magnetic fields such as an additional low-temperature peak in the specific heat and an enhanced magnetocaloric effect.