Spin-wave thermodynamics of square-lattice antiferromagnets revisited

Abstract

Modifying the conventional spin-wave theory in a novel manner based on the Wick decomposition, we present an elaborate thermodynamics of square-lattice quantum antiferromagnets. Our scheme is no longer accompanied by the notorious problem of an artificial transition to the paramagnetic state inherent in modified spin waves in the Hartree-Fock approximation. In the cases of spin $\frac{1}{2}$ and spin $1$, various modified-spin-wave findings for the internal energy, specific heat, static uniform susceptibility, and dynamic structure factor are not only numerically compared with quantum Monte Carlo calculations and Lanczos exact diagonalizations but also analytically expanded into low-temperature series. Modified spin waves interacting via the Wick decomposition provide reliable thermodynamics over the whole temperature range of absolute zero to infinity. Adding higher-order spin couplings such as ring exchange interaction to the naivest Heisenberg Hamiltonian, we precisely reproduce inelastic-neutron-scattering measurements of the high-temperature-superconductor-parent antiferromagnet ${\mathrm{La}}_2{\mathrm{CuO}}_4$. Modifying Dyson-Maleev bosons combined with auxiliary pseudofermions also yields thermodynamics of square-lattice antiferromagnets free from thermal breakdown, but it is less precise unless temperature is sufficiently low. Applying all the schemes to layered antiferromagnets as well, we discuss the advantages and disadvantages of modified spin-wave and combined boson-pseudofermion representations.

Phys. Rev. B, in press

References in corpus (6)

• Anomalous High-Energy Spin Excitations in La2CuO4
• Quantum dynamics and entanglement of spins on a square lattice
• Low energy theory of the t-t'-t''-U Hubbard Model at half-filling: interaction strengths in cuprate superconductors and an effective spin-only description of La_2CuO_4
• Spectrum of short-wavelength magnons in two-dimensional quantum Heisenberg antiferromagnet on a square lattice: third order expansion in 1/S
• Towards the theory of ferrimagnetism
• Evidence for multimagnon-mediated nuclear spin relaxation in the intertwining double-cain ferrimagnet $C{a}_{3}C{u}_3(P{O}_4{)}_4$

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• Magnon Spectra of Cuprates beyond Spin Wave Theory
• Thermal features of Heisenberg antiferromagnets on edge- versus corner-sharing triangular-based lattices: A message from spin waves
• Magnon Confinement on the Two-Dimensional Penrose Lattice: Perpendicular-Space Analysis of the Dynamic Structure Factor
• Polarized Raman Response of Two-Dimensional Quasiperiodic Antiferromagnets: Configuration-Interaction versus Green's Function Approaches
• Breakdown of the conventional spin-wave dynamics and its double-constraint modification in the spin-$\frac{1}{2}$ triangular-prism Heisenberg antiferromagnet
• Raman Characterization of Two-Dimensional Quasiperiodic Antiferromagnets on Various Lattices: Spin-Orbit Mechanism