Magnetic Phase Transition in a Highly Disordered Cuprate Near the Percolation Threshold

We propose to investigate the magnetic phase transitions in the highly disordered cuprate LiCu₃O₃. This frustrated spin-1/2 square-lattice Heisenberg antiferromagnet features two types of edge-sharing CuO planes, where magnetic Cu²⁺ ions are randomly substituted by non-magnetic Li⁺ ions at 20% and 40% concentrations, respectively. The moderately diluted planes (20%) undergo long-range antiferromagnetic order below Tc1 ≈ 124 K, while the highly diluted planes (40%) reside near the classical percolation threshold (pc ≈ 0.41) and exhibit a second, yet poorly understood, magnetic transition below Tc2 ≈ 30 K.
This unique material offers a rare opportunity to study magnetic ordering phenomena in a regime dominated by strong disorder and frustration. Our primary goal is to elucidate the nature of the magnetic phase emerging near the percolation threshold, using elastic and inelastic neutron scattering techniques. These measurements will allow us to determine both the static spin structure and the low-energy excitations of this disordered antiferromagnet, shedding light on criticality, spin correlations, and dynamic properties in the vicinity of percolation-driven quantum phase transitions.
Understanding such systems is crucial for developing a comprehensive framework of disordered magnetism and may have broader implications for quantum materials where randomness and interactions compete on equal footing.