Dense Kondo behavior and many other effects in metallic point-contacts of rare-earth hexaborides

Point-contact spectra of rare-earth (La, Ce, Gd, Tb, and Dy) hexaborides are reported and compared with their electrical resistivity. Two important points are discussed as an experimental guide of point-contact spectroscopy (PCS). One is the difference between the PCS and a tunneling experiment. The other is the problem of reproducibility, i.e., differences in the observed spectra between different contacts. Examples of these problems are discussed for the PCS of rare-earth hexaboride homocontacts. Based on the above discussions the dense Kondo behavior of CeB6 is lastly discussed.