Scanning Tunneling Spectroscopy on Organic Superconductors

概要

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The superconducting phase of organic superconductors (BEDT-TTF)2X was studied by electron tunneling using scanning tunneling microscope (STM). Tunneling both at the conducting plane and lateral surfaces was performed on single crystals of (BEDT-TTF)2Cu(NCS)2. The tunneling conductance curve obtained at the conducting plane is explained by $d$-wave gap symmetry. Tunneling spectra at lateral surfaces vary depending on the tunneling direction, suggesting the in-plane anisotropy of the gap. The directional dependence is also consistent with $d$-wave symmetry with line nodes $\pi/4$ from the $k_{b}$- and $k_{c}$-axes. This indicates that the superconducting pair wave function has $d_{x^{2}-y^{2}}$-wave symmetry. Protonated and partially deuterated (BEDT-TTF)2Cu[N(CN)2]Br samples were also studied. Tunneling spectra are consistent with $d$-wave symmetry in all salts. Gap parameters are obtained as functions of the effective correlation. The large gap value suggests the strong coupling superconductivity. The zero-bias conductance peak, which is evidence for nodes of the superconducting gap, was found.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2006-03-15