Untersuchung der Andreev-Reflexion an Schwer-Fermion (HF)/Supraleiter-Grenzflächen bei tiefen Temperaturen mittels Punktkontaktspektroskopie.

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Strong interactions among the electrons lead in heavy-fermion superconductors (HFS) to strongly enhanced electron masses in comparison to normal metals (N). Due to the nature of the strong electron-electron interactions some HFS compounds show strong evidence that the symmetry of the superconducting wave function corresponds to states with higher angular momentum (p-, d-wave etc.) in comparison to s-wave superconductors, leading to unconventional behavior. Point-contact spectroscopy (PCS) of N/HFS contacts is a strong method to investigate the symmetry and related properties of the superconducting wave function. Unfortunately, up to now the basic process of Andreev reflection (AR) underlying in PCS, which describes the electron-hole conversion at the N/HFS interface, is not understood in detail. Although the magnitude of this process should be strongly suppressed by the large mismatch of the effective electron masses in N and HFS, a significant Andreev signal in the differential conductance versus voltage has been measured in many experiments. It has been proposed that only the effective masses without strong interactions determine the boundary conditions at the N/HFS interface. In search of an effect of the effective electron mass on the Andreev signal, we propose to investigate the reverse configuration, where the heavy-fermion component in the normal conducting state is in contact with a conventional superconductor. Specifically we will use point-contacts consisting of CeColn5 single crystals with different effective masses and conventional superconductors as a counter electrode. The Andreev signal shall be investigated in detail and should enlighten the role of the effective mass in the Andreev reflection process.