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

与正常金属(N)相比，重费密子超导体(HF)中电子之间的强相互作用使电子质量大大增加。由于强电子-电子相互作用的性质，一些HFS化合物显示出强有力的证据表明，超导波函数的对称性对应于具有较高角动量的状态(p波、d波等)。与S波超导体相比，导致了非常规行为。N/HFS接触的点接触谱(PCS)是研究超导波函数对称性及其相关性质的有力手段。不幸的是，到目前为止，描述N/HFS界面上电子-空穴转换的PCS中的安德烈夫反射(AR)的基本过程还没有被详细地了解。虽然这一过程的大小应该被N和HFS中有效电子质量的大失配所强烈地抑制，但在许多实验中已经测量到了在微分电导-电压中显著的安德烈夫信号。提出了只有没有强相互作用的有效质量才能决定N/HFS界面的边界条件。为了寻找有效电子质量对Andreev信号的影响，我们建议研究正常导电态的重费米子分量与常规超导体接触的反向组态。具体地说，我们将使用由不同有效质量的CeColn5单晶和常规超导体组成的点接触作为对电极。安德列夫信号应该被详细地研究，并且应该启发有效质量在安德列夫反射过程中的作用。

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.