Honeycomb Heisenberg spin ladder: Unusual ground state and thermodynamic properties

¹ Theoretical Condensed Matter Physics and Computational Materials Physics Laboratory, School of Physics, University of Chinese Academy of Sciences - P. O. Box 4588, Beijing 100049, China
² College of Chemistry and Molecular Engineering, State Key Laboratory of Rare Earth Materials Chemistry and Applications, Peking University - Beijing 100871, China

^(a) gsu@ucas.ac.cn (corresponding author)

Received: 30 July 2013
Accepted: 2 December 2013

Abstract

The unusual ground state and thermodynamic properties of spin-(1/2) two-leg honeycomb (HC) spin ladder are systematically studied by jointly utilizing various analytical and numerical methods. The HC spin ladder is found to exhibit behaviors dramatically different from those of the conventional square spin ladder. A strong relevant term and a half saturation magnetization plateau that can be attributed to the formation of diluted dimer states are observed in the HC ladder, both of which are absent in the square ladder. The ground state phase diagram of the HC spin ladder is identified, and the thermodynamic properties of the specific heat and susceptibility for different couplings are thoroughly explored, where two kinds of excitations are unveiled. Our calculated result is well fitted to the experimental data of the two-leg HC spin ladder compound [Cu₂L¹(N₃)₄]_n.