Glittum, C.; Syljuåsen, O. F.: Field-induced multi-Q → states in a pyrochlore Heisenberg magnet. Physical Review B 111 (2025), p. 214444/1-18
10.1103/5rsg-2klm
Open Access Version
Abstract:
We construct exact ground states of the 𝐽1−𝐽3𝑏classical Heisenberg model on the pyrochlore lattice in the presence of a magnetic field. They are noncoplanar multi-𝑄 spin configurations with a large magnetic unit cell that generalize the previously found coplanar sublattice pairing states. Using linear spin-wave theory, we show that entropy favors these multi-𝑄 states at low temperatures in high magnetic fields. This is confirmed by Monte Carlo simulations, and a phase diagram is constructed. We also calculate the zero-temperature dynamical structure factor. Besides the usual Goldstone modes associated with the ordering 𝑄s, we find high intensity gapless modes at momenta where there are no Bragg peaks.