2013/11/13 by Anson W. C. Wong, Zhihao Hao, Michel J. P. Gingras · 1 citation
Physics and Astronomy · #cond-mat.str-el
paper · pdf · doi:10.1103/physrevb.88.144402
published as Phys. Rev. B 88, 144402 (2013) · 8 pages, 3 figures. Version is the same as the published one, within epsilon
arxiv created 2013/11/13 · arxiv updated 2013/11/15
Motivated by recent experimental and theoretical progress on the Er2Ti2O7 pyrochlore XY antiferromagnet, we study the problem of quantum order-by-disorder in pyrochlore XY systems. We consider the most general nearest-neighbor pseudo spin-1/2 Hamiltonian for such a system characterized by anisotropic spin-spin couplings Je = [J_±, J±±, Jz±, Jzz] and construct zero-temperature phase diagrams. Combining symmetry arguments and spin-wave calculations, we show that the ground state phase boundaries between the two candidate ground states of the Γ5 irreducible representation, the ψ2 and ψ3 (basis) states, are rather accurately determined by a cubic equation in J±J±±)/Jz±2. Depending on the value of Jzz, there can be one or three phase boundaries that separate alternating regions of ψ2 and ψ3 states. In particular, we find for sufficiently small Jzz/J± a narrow ψ2 sliver sandwiched between two ψ3 regions in the J±±/J_± vs Jz±/J_± phase diagram. Our results further illustrate the very large potential sensitivity of the ground state of XY pyrochlore systems to minute changes in their spin Hamiltonian. Using the experimentally determined J3 and g-tensor values for Er2Ti2O7, we show that the heretofore neglected long-range 1/r3 magnetostatic dipole-dipole interactions do not change the conclusion that Er2Ti2O7 has a ψ2 ground state induced via a quantum order-by-disorder mechanism. We propose that the CdDy2Se4 chalcogenide spinel, in which the Dy3+ ions form a pyrochlore lattice and may be XY-like, could prove interesting to investigate.