Abstract
We use a second-order rotational invariant Green's-function method (RGM) and the high-temperature expansion (HTE) to calculate the thermodynamic properties of the kagome-lattice spin- Heisenberg antiferromagnet with nearest-neighbor exchange . While the HTE yields accurate results down to temperatures of about , the RGM provides data for arbitrary . For the ground state we use the RGM data to analyze the dependence of the excitation spectrum, the excitation velocity, the uniform susceptibility, the spin-spin correlation functions, the correlation length, and the structure factor. We found that the so-called ordering is more pronounced than the ordering for all values of . In the extreme quantum case , the zero-temperature correlation length is only of the order of the nearest-neighbor separation. Then we study the temperature dependence of several physical quantities for spin quantum numbers . As increases, the typical maximum in the specific heat and that in the uniform susceptibility are shifted toward lower values of , and the height of the maximum is growing. The structure factor exhibits two maxima at magnetic wave vectors corresponding to the and state. We find that the short-range order is more pronounced than the short-range order for all temperatures . For the spin-spin correlation functions, the correlation lengths, and the structure factors, we find a finite low-temperature region , where these quantities are almost independent of .
11 More- Received 15 March 2018
- Revised 29 June 2018
DOI:https://doi.org/10.1103/PhysRevB.98.024414
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