Atomic structures and nanoscale electronic states on the surface of MgB2 superconductor observed by scanning tunneling microscopy and spectroscopy

• Published in: Low temperature physics (Woodbury, N.Y.) N.Y.), 2019-11, Vol.45 (11), p.1209-1217
• Main Authors: Sugimoto, Akira, Yanase, Yuta, Ekino, Toshikazu, Muranaka, Takahiro, Gabovich, Alexander M.
• Format: Article
• Language: English
• ISSN: 1063-777X; 1090-6517
• DOI: 10.1063/10.0000132

The systematic study of the nanoscale local electronic states on the MgB2 surface was performed using the low-temperature scanning tunnel microscopy/spectroscopy (STM/STS). The STM topography shows the atomic image of the hexagonal lattice with the constant parameter a’ = 0.31 nm, which is identified as mainly the Mg site occupancy. The temperature-dependent STS measurements were analyzed assuming the existence of two energy gaps. As a result, the fitting gap amplitudes Δfit  ≃  10.2 meV and 4.8 meV were found at T = 4.9 K. The scanned conductance (dI/dV) maps in the area of 4 × 2 nm2 show homogenous distributions of the gaps associated with the π-band. In addition, the conductance peaks at zero-bias voltage were observed through defined lines with lengths about ∼0.8 nm, which is much smaller than the superconducting coherence length ξ a b ∼ 40 nm of MgB2. The form of the zero-bias peaks looks like that in the case of the Andreev-Saint-James reflection at the tip-sample contact.