1. Mingxiang Xu,  Yoshihiko Takano, Takeshi Hatano, Masayo Kitahara, Daisuke Fujita National Institute for Materials Science, Tsukuba, Japan LT 23, Hiroshima, JAPAN  E-mail: XU.Mingxiang@nims.go.jp

2. ABSTRACT §Reproducible, clean and stable MgB 2 superconducting tips have been fabricated. §The quality of these tips has been verified by imaging the surface of a thin Au(111) film using a low temperature STM. §High-quality semi-atomically resolved STM images of the thin Au(111) film sample have been observed.

3. BACKGROUND & MOTIVATIONS §Conventional STM studies for superconducting materials: superconductor/insulator/normal-metal (S/I/N) configuration. §Quasiparticle tunneling using a superconducting atomically sharp Nb tip: S/I/S measurements, OK! §MgB 2 : Suitable for use as STM tips? Feasible? §Josephson tunneling in SS-STM: Tunable Josephson junction !!

4. Fig. 1. (a) Optical image of the MgB 2 tip. (b) Enlarged image.

5. Fig. 2. Schematic depiction of the experimental setup

6. Fig. 3.

7. A wide-area STM image (104 × 104 nm 2 ) at the constant-height mode (V T = -2.00 V, I T = 0.20 nA) of the reconstructed Au(111) surface observed at 30 K, clearly showing the steps of monoatomic height and the herringbone patterns.

8. F Further STM studies by the MgB 2 tip §MgB 2 superconducting tip + MgB 2 sample. §MgB 2 two gaps nature. §SS-STM: Tunable Josephson junction.

9. Fig. 4. Schematic depiction for further experiments

10. CONCLUSION §Reproducible, clean and stable MgB 2 superconducting tips have been fabricated. §MgB 2 : Suitable for use as STM tips, is feasible! §Application: Josephson tunneling in SS-STM: Tunable Josephson junction !!