STM spectroscopy of (MDT-TTF)2AuI2

The electron tunneling was performed on the superconducting phase of (MDT-TTF)2AuI2 using STM. The tunneling differential conductance at T=1.4 K shows the superconducting energy gap structure clearly. The conductance near zero bias voltage is well reduced while the enhancement at the gap edge is observed. The obtained gap Δ0=2 meV (2Δ0/kTc=12) is larger than that of the weak coupling limit. The shape of the spectrum, which is different from the BCS density of states, suggests the gap anisotropy. The tunneling spectrum is explained by the d-wave. The conductance well above Tc is flat. On the other hand, the pseudo gap like structre is obseved near Tc.