Tracking the Evolution from Single Ion Effects to Many-Body Correlations*

NaYbSe₂ belongs to a recently discovered class of delafossites, a number of which exhibit the hallmarks typical of a quantum spin liquid. These include the absence of long-range magnetic order, persistent spin fluctuations [Bordelon et al., Nature Physics (2019)], and a large anomalous heat capacity [Ranjith et al., PRB (2019)], all at the lowest measurable temperatures. In a previous study, we were successful in growing the doping series NaYb_xLu_1-xSe₂, substituting Yb³⁺ for non-magnetic Lu³⁺. This allowed us to demonstrate the evolution of magnetic interactions from single ion effects at low Yb doping to highly-correlated many-body entanglement in NaYbSe₂ [Pritchard Cairns et al., PRB (2022)]. Seeking a more quantitative analysis, we have performed pulsed field magnetization measurements in fields of up to 60 T. By modeling the results obtained for different dopings and temperatures, we are able to shed light on the correlations in the full magnetic compound and on this broader class of quantum spin liquid candidate materials.