(07E124) Crystal field excitations in CeCu_2Ge_2: Revisited employing a single crystal and inelastic neutron scattering

摘要

The intermetallic compound, CeCu_2Ge_2, is the counterpart of the heavy-fermion superconductor CeCu_2Si_2. CeCu_2Ge_2 is a magnetically ordering (T_N=4.1 K) Kondo lattice with a moderate Sommerfeld coefficient of 140 mJ/ mol K~2. Earlier inelastic neutron measurements on a polycrystalline sample revealed a doublet ground state and a quasi-quartet excited state at 16.5 meV, although a splitting of the 4f~1 (J = 5/2) ground state multiplet into 3 doublets is expected from the point symmetry of the Ce~(3+) ions. We performed detailed inelastic neutron scattering experiments on a single crystal at the thermal triple-axis spectrometer PUMA at FRM II for different crystallographic directions. From our results we infer that the quasi-quartet, in fact, consists of two doublets at 17.0 and 18.3 meV which exhibit a strong directional dependence of their transition matrix elements to the ground state doublet. Finally, we will present a new set of crystal field parameters.