Abstract
In the search for quantum entangled states of matter, materials with triangular lattices of antiferromagnetically interacting magnetic ions remain a focal point. We report the magnetic phase diagram and excitations of a spin-1⁄2 easy axis triangular lattice antiferromagnet, K2Co(SeO3)2. While there is no sharp specific heat anomaly in zero field, there is a prominent magnetization plateau phase at 1/3 of the saturation magnetization. For 1.1 T< B < 21 T this plateau phase is marked by a second order phase boundary, which however, terminates at (T, B) = (4.5(2) K, 1.1(1) T). Neutron diffraction reveals persistent two-dimensional √3×√3 magnetic order for T < 12 K and B = 0 T that can be described as an antiferromagnetic honeycomb lattice. Neutron spectroscopy uncovers low energy continuum scattering at zero field that we associate with the quantum disordered spins within honeycombs. In the plateau phase these spins become magnetized and the system supports coherent spin waves. From their dispersion relation we infer the spin Hamiltonian, which features nearest neighbor interactions with Jz = 2.95(3) meV and Jxy = 0.26(2) meV.
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Tong Chen is currently a postdoctoral fellow working with Prof. Collin Broholm at Johns Hopkins University. His research focuses on exploring quantum magnetism through neutron diffraction and scattering techniques. Tong earned his Ph.D. in physics from Rice University in 2021, where he worked under the guidance of Prof. Pengcheng Dai, investigating unconventional superconductors using neutron scattering methods.
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