Evidence for unconventional superconductivity in UPd₂Al₃ thin films

Abstract

The superconducting energy gap of UPd₂Al₃ thin films was investigated by quasiparticle tunneling spectroscopy. Planar cross junctions were prepared by MBE thin-film deposition, photolithography and ion-beam etching completed by a lift-off process. The measured differential conductance dI/dV clearly revealed the tunneling density of states. At temperatures below 1K we identified a BCS-like differential tunneling density of states along the c-axis with 2Δ (0K)/k_BT_c≈3.8. At higher temperatures a crossover toa V-shaped differential conductance develops. We propose this to be evidence for nodes in the superconducting energy gap. Measurements were performed at various magnetic fields and temperatures between 0.3K and T_c≈2K. The experimental observations are discussed in the framework of unconventional superconductivity.