Magnon specific heat of high- [formula omitted] parent compounds La 2CuO 4 and Y Ba 2Cu 3O 6 : Green’s function approach

Abstract

We calculate the temperature dependence of the magnon contribution to specific heat of the high- T C superconducting parent compounds La 2CuO 4 and Y Ba 2Cu 3O 6 using the Green’s function (GF) method within the Tyablikov’s approximation (RPA). By making use of quantum Heisenberg S = 1 2 three-dimensional antiferromagnetic model, we obtain the specific heat temperature dependence in the whole temperature range from absolute zero to the Néel temperature. The analysis performed for La 2CuO 4 suggests that the magnon contribution to the total specific heat measured in the experiment is small, but not negligible as predicted by the simplified two-dimensional model often used within the linear spin-wave (LSW) theory. This discrepancy originates from the renormalization of the magnon energies due to the RPA in GF approach. Further, we discuss the influence of the in-plane frustration and the three-dimensionality of the system on the magnon specific heat in La 2CuO 4. We study the low-temperature behavior of the specific heat as well as the behavior in the vicinity of the Néel temperature which gives for the critical exponent α value α = − 1 2 . Finally, we tend to improve the LSW theory results found in the literature by applying that theory to the three-dimensional orthorhombic model with second- and third-neighbor exchange interaction.