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STM Spectroscopy on Anisotropic Superconductors |
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| Authors: | K Ichimura T Arai K Nomura S Takasaki J Yamada S Nakatsuji H Anzai T Nakamura T Takahashi B Hilti and J S Zambounis |
| Affiliation: | (1) Hokkaido University, Sapporo, 060-0810, Japan;(2) Department of Material Science, Himeji Institute of Technology, Hyogo, 678-1201, Japan;(3) Department of Physics, Gakushuin University, Tokyo, 171-0031, Japan;(4) Central Research Laboratories, Ciba-Geigy AG, 4000 Basel, Switzerland |
| Abstract: | The superconducting phase of organic superconductors  -(BEDT-TTF)2Cu(NCS)2 and (MDT-TTF)2AuI2 was investigated by the electron tunneling spectroscopy using low temperature STM. The tunneling differential conductance at the lateral surface of -(BEDT-TTF)2Cu(NCS)2 varies its shape depending on the tip direction. The in-plane anisotropy of the conductance is well explained by the d-wave symmetry with line nodes along the direction 45° from the c-axis. For (MDT-TTF)2AuI2, the tunneling conductance at T = 1.4 K shows the superconducting energy gap structure clearly. The finite conductance inside the gap edge suggests the gap anisotropy. The tunneling spectrum is explained by the d-wave pairing. The obtained gap  0 = 2 meV (20/kT
c
= 12) is larger than that of the weak coupling limit. The pseudogap structure is observed near T
c
. |
| Keywords: | STM electron tunneling organic superconductors pairing symmetry |
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