In quantum magnets with order-by-disorder, the pseudo-Goldstone gap grows with temperature as T^(d+1) for linear modes and T^(d/2+1) for quadratic modes, computable through a new linear-spin-wave curvature formula.
Pyrochlore antiferromagnet with antisymmetric exchange interactions: critical behavior and order from disorder
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abstract
We investigate the nature of phase transitions induced by Dzyaloshinskii-Moriya (DM) interactions on a classical pyrochlore antiferromagnet. For both symmetry-allowed antisymmetric exchange interactions, the macroscopic degeneracy due to geometrical frustration is relieved and a long-range magnetic order appears in the ground state. We find an Ising-like phase transition in the case of direct DM interaction which selects a doubly degenerate all-in all-out magnetic order. In the presence of indirect DM coupling, the magnet undergoes an XY-like phase transition into a state with broken Z6 symmetry. We show that the critical behavior in both cases is modified due to the constrained spin fluctuations in the correlated Coulomb phase. We also demonstrate an interesting order from disorder phenomenon where the system switches between two distinct types of broken Z6 symmetry.
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Universal temperature-dependent power law excitation gaps in frustrated quantum spin systems harboring order-by-disorder
In quantum magnets with order-by-disorder, the pseudo-Goldstone gap grows with temperature as T^(d+1) for linear modes and T^(d/2+1) for quadratic modes, computable through a new linear-spin-wave curvature formula.