Excitation spectrum and spin Hamiltonian of the frustrated quantum Ising magnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Pr</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>BWO</mml:mi><mml:mn>9</mml:mn></mml:msub></mml:mrow></mml:math>
J. Nagl, D. Flavián, Shohei Hayashida, K. Yu. Povarov, M. Yan, Naoki Murai, Seiko Ohira‐Kawamura, G. Simutis, T. J. Hicken, H. Luetkens, C. Baines, A. Hauspurg, B. V. Schwarze, F. Husstedt, Vladimir Pomjakushin, T. Fennell, Z. Yan, S. N. Gvasaliya, A. Zheludev
Abstract
We present a thorough experimental investigation on of the rare-earth based frustrated quantum antiferromagnet <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi>Pr</a:mi><a:mn>3</a:mn></a:msub><a:msub><a:mi>BWO</a:mi><a:mn>9</a:mn></a:msub></a:mrow></a:math>, 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. Published by the American Physical Society 2024