Isolating multi-particle dynamic correlations in quantum Heisenberg spin1/2 chain

The ability to access the spin dynamical structure factor, a two-particle correlation function in space and time, has revolutionized our understanding of emergent quantum phases, quantum phase transitions, and universality in strongly correlated materials [1]. Nevertheless, to fully reveal the rich dynamics of these complex systems, such as dynamic correlations in spin liquids and universality class of integrable spin chains, one requires new measurements capable of accessing higher-order correlation functions that encode hidden information about the quantum dynamics of the system [2]. Focusing on a paradigmatic quantum many-body phenomenon --- fractionalization in a Heisenberg spin-1/2 chain Sr₂CuO₃ --- we demonstrate unprecedented access to both the two- and the multi-particle dynamical spectral weight using resonant inelastic x-ray scattering, by tuning to different intermediate states of the many-body system. By comparing our measurements to exact diagonalization calculations of the t-J Hamiltonian, we show that the dynamical spectral weight evolutions of two- and multi-particle correlations are distinct and are separated by an energy scale given by the cost to break a singlet state in the chain. Our results, demonstrate how distinct intermediate states in the RIXS process can be leveraged to access new quantum many-body correlations that are not easily accessible to other spectroscopic probes. Hence, we establish RIXS as a robust diagnostic tool for fractionalization and universality class in quantum materials. Furthermore, control over the multi-particle dynamics, using energy-detuning in RIXS as a knob, can open new pathways to explore quantum information in many body states realized in quantum materials.

[1] R. Coldea et al. Phys. Rev. B 68, 134424 (2003), C. Ruegg et.al., Phys. Rev. Lett. 100, 205701 (2008), R. Coldea et. al. Science 327, 177 (2010), D. Blosser et. al., Phys. Rev. Lett. 121, 247201 (2018).

[2] Z. Zhu et al. Phys. Rev. Lett. 119, 157201 (2017), J. Knolle et al., Annu. Rev. Condens. Matter Phys. 10, 451 (2019), Z. Kranik et al., Phys. Rev. Lett. 132, 017101 (2024). E. Rosenberg et al., Science 384, 48 (2024).