Crystalline electric field excitations in the heavy fermion superconductor CeCoIn5

The crystalline electric field (CEF) energy level scheme of the heavy fermion superconductor CeCoIn5 has been determined by means of inelastic neutron scattering (INS). Peaks observed in the INS spectra at ∼8 and ∼27 meV with incident neutron energies between Ei=30 and 60 meV and at a temperature T=10 K correspond to transitions from the ground state to the two excited states, respectively. The wave vector and temperature dependence of these peaks are consistent with CEF excitations. Fits of the data to a CEF model yield the CEF parameters B20=−0.80 meV, B40=0.059 meV, and |B44|=0.137 meV corresponding to an energy level scheme: Γ7(1)(0)[=0.487|±5/2〉−0.873|∓3/2〉], Γ7(2)(8.6 meV,100 K), and Γ6(24.4 meV,283 K).