EVIDENCE FOR UNCONVENTIONAL SUPERCONDUCTIVITY IN UPD2AL3 THIN-FILMS

The superconducting energy gap of UPd2Al3 thin films was investigated by quasiparticle tunneling spectroscopy. Planar cross junctions were p repared by MBE thin-film deposition, photolithography and ion-beam etc hing completed by a lift-off process. The measured differential conduc tance dI/dV clearly revealed the tunneling density of states. At tempe ratures below 1K we identified a BCS-like differential tunneling densi ty of states along the c-axis with 2 Delta(0K)/k(B)T(c) similar or equ al to 3.8. At higher temperatures a crossover to a V-shaped differenti al conductance develops. We propose this to be evidence for nodes in t he superconducting energy gap. Measurements were performed at various magnetic fields and temperatures between 0.3K and T-c similar or equal to 2K. The experimental observations are discussed in the framework o f unconventional superconductivity.