Magnetic dynamics of bilayer cuprate superconductors

Abstract

In the present paper, we use the Heisenberg antiferromagnetic model within linear spin-wave theory to study the magnetic dynamics of bilayer antiferromagnets such as YBa2Cu3O6+x. The Zubarev’s double-time Green’s-function formalism has been employed in order to evaluate the expressions for spin-wave dispersion, sublattice magnetization, and specific heat. It has been shown that in these systems, the intrabilayer coupling leads towards a “spin gap.” The optical mode is found to contribute significantly to the sublattice magnetization only in the high-temperature regime. In the low-temperature regime, the contribution from the acoustic mode is sensitive to the anisotropy term. We observe that the dipolar anisotropy does not produce the three-dimensional (3D) Néel ordering, while the exchange anisotropy is essential to keep 3D Néel ordering in these systems. Further, we observe a crossover from 3D to quasi-2D behavior at a certain temperature. The presence of the optic mode does not seem to alter the quasi-2D behavior of these systems in the higher temperature regime. The specific heat is also found to be dependent on the ratio of intrabilayer to in-plane coupling strength (r). These results are compared with the existing results.

Source-reported materials — not catalogue approval

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