STM spectroscopy of an organic superconductor |
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| Institution: | 1. Department of Physics, Hokkaido University, Sapporo 060, Japan;2. Department of Material Science, Himeji Institute of Technology, Hyogo 678-12, Japan;1. College of Vehicle and Traffic Engineering, Henan University of Science and Technology, Luoyang, 471003, China;2. School of Environmental Science & Engineering, Tianjin University, Tianjin, 300350, China;1. Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, China;2. CNPC Key Laboratory of Oil & Gas Reservoir Stimulation, Langfang 065007, China;1. Shenzhen Institute for Quantum Science and Engineering and Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China;2. School of Physics, Peking University, Beijing 100871, China;3. Guangdong Provincial Key Laboratory of Computational Science and Material Design, Southern University of Science and Technology, Shenzhen 518055, China;4. Shenzhen Key Laboratory of Advanced Quantum Functional Materials and Devices, Southern University of Science and Technology, Shenzhen 518055, China;1. State Key Laboratory of Reliability and Intelligence of Electrical Equipment, Hebei University of Technology, Tianjin 300130, China;2. School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130, China;3. Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparation Technology, School of Science, Tianjin University, Tianjin 300354, China |
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| Abstract: | Electron tunneling spectroscopy of the organic superconductor κ-(BEDT-TTF)2Cu(NCS)2using low temperature scanning tunneling microscope (STM) is reported. The tunneling differential conductance in the superconducting phase was obtained in theb–cplane of a single crystal, by varying the tip position on the sample surface. The differential conductance is reduced near zero bias voltage and enhanced at the gap edge, associated with the superconducting gap structure belowformula] K. The gap width differs slightly from sample to sample, while the overall functional shape of the conductance is sample-independent. The tunneling conductance is reduced to almost zero near zero bias voltage, while it is finite inside the gap edge. The curve obtained cannot be fit to the BCS density of states withs-wave pairing symmetry, even if the life-time broadening of one-electron levels is taken into account. Finite conductance inside the gap edge suggests anisotropy of the gap. However, the conductance curve obtained is not explained by a simpled-wave symmetry for Δ(k). The reduced conductance near zero bias voltage suggests a finite gap. An anisotropic model with a finite gap, in which Δ(k) varies depending on the direction ink-space, is examined. The tunneling conductance in the low-energy region is almost fit by the model with Δmin = 2 meV and Δmax = 6 meV. The finite conductance is explained by introducing a small effect of life time broadening. We conclude that the gap is anisotropic and is finite (at least Δmin = 2 meV) on the entire Fermi surface. |
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