Geometric frustration and Dzyaloshinskii-Moriya interactions in a quantum star lattice hybrid copper sulfate

Abstract

We study the magnetism of a layered, spin-$\frac{1}{2}$ organic-inorganic copper sulfate, which is a close realization of the star lattice antiferromagnet, one of the playgrounds of geometric frustration and resonating valence bond physics in two spatial dimensions. Our thermodynamic measurements show no ordering down to 0.1 K and a characteristic field-induced entropic shift, revealing the presence of an infinite number of competing states down to very low energy scales. The response to external magnetic fields shows, in addition, a peculiar anisotropy, reflected in the formation of a 1/3 magnetization plateau (stable up to full saturation around 105 T) and a paramagnetic, Curie-like susceptibility for one direction of the field ($\mathbf{H}\parallel \mathbf{c}$), and a completely different response in other field directions. Our first-principles density functional theory calculations and exact diagonalizations show that these experimental puzzles are distinctive signatures of a strong interplay between geometric frustration and sizable Dzyaloshinskii-Moriya interactions, and the emergence of a continuous U(1) symmetry at low energy scales.

7 pages, 3 figures + Supplemental Material, accepted in Phys. Rev. B (Letter)

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Cited by in corpus (3)

• High Chern numbers and topological flat bands in high-field polarized Kitaev magnets on the star lattice
• Symmetry breaking and competing valence bond states in the star lattice Heisenberg antiferromagnet
• Spin Nernst and thermal Hall effects of topological triplons in quantum dimer magnets on the maple-leaf and star lattices