Excitation spectrum and spin Hamiltonian of the frustrated quantum Ising magnet Pr 3 BWO 9

• Published in: Physical review research 2024-06, Vol.6 (2), Article 023267
• Main Authors: Nagl, J., Flavián, D., Hayashida, S., Povarov, K. Yu, Yan, M., Murai, N., Ohira-Kawamura, S., Simutis, G., Hicken, T. J., Luetkens, H., Baines, C., Hauspurg, A., Schwarze, B. V., Husstedt, F., Pomjakushin, V., Fennell, T., Yan, Z., Gvasaliya, S., Zheludev, A.
• Format: Article
• Language: English
• ISSN: 2643-1564; 2643-1564
• DOI: 10.1103/PhysRevResearch.6.023267

We present a thorough experimental investigation on of the rare-earth based frustrated quantum antiferromagnet Pr 3 BWO 9 , a purported spin-liquid candidate on the breathing kagome lattice. This material possesses a disordered ground state with an unusual excitation spectrum involving a coexistence of sharp spin waves and broad continuum excitations. Nevertheless, we show through a combination of thermodynamic, magnetometric, and spectroscopic probes with detailed theoretical modeling that it should be understood in a completely different framework. The crystal field splits the lowest quasidoublet states into two singlets moderately coupled through frustrated superexchange, resulting in a simple effective Hamiltonian of an Ising model in a transverse magnetic field. While our neutron spectroscopy data do point to significant correlations within the kagome planes, the dominant interactions are out-of-plane, forming frustrated triangular spin-tubes through two competing ferro-antiferromagnetic bonds. The resulting ground state is a simple quantum paramagnet, where the presence of strongly hyperfine-coupled nuclear moments and weak structural disorder causes significant modifications to both thermodynamic and dynamic properties.