uSR Insights into Spin Dynamics within Magnetically Frustrated Intermetallic YbCuAs_2

This study investigates the intermetallic Kondo-lattice system YbCuAs$_2$\ using muon spin relaxation/rotation ($\mu$SR) techniques, comparing the observed local magnetic response with reported macroscopic transport and thermodynamic phenomena. Long-range magnetic ordering is confirmed below the temperature $T = 3.7$ K, contrary to the findings from neutron diffraction measurements. Spontaneous muon spin precession frequencies below the phase transition yield the local magnetic field and evolution of the sublattice magnetization. Above the ordering temperature, four regimes in temperature are observed using $\mu$SR, which correlates directly with features in specific heat and resistivity measurements. Density functional theory calculations suggest three potential muon sites, while point charge crystal electric field calculations yield the electronic energy levels of the Yb$^{3+}$ ion in its crystalline environment. Additionally, calculations of the muon spin-lattice relaxation rate and nuclear dipolar field at the muon sites provide a more comprehensive picture of the electronic and nuclear contributions to the $\mu$SR signal.