Tunneling density of states of the Kondo superconductor (La1−x Ce x )Al2

Tunneling measurements on (La_1?x Ce _x )Al₂ single crystals (x=0; 0.001; 0.002) were performed at 0.1 K. Heavily dopedp-type GaAs/Zn acts as normal conducting counterelectrode where the Schottky-barrier provides the insulating layer for tunneling. Contact between counterelectrode and sample surface is not made before cooling down to 1 K. Contamined surface layers can be pierced mechanically at 0.1 K. The extremely gapless behaviour agrees with an impurity band positiony ₀<0.8 for localized exited states, although no detailed structure can be resolved.