The tunneling spectra and superconducting gaps observed by using scanning tunneling microscope near the grain-boundary of FeSe0.3Te0.7 films

摘要

We used STM to study the tunneling spectra of FeSe0.3Te0.7 films with twoorientations of ab-planes and the connection ramp between them. We havediscovered that, using pulse laser deposition (PLD) method, the a- and b-axisof the FeSe0.3Te0.7 film deposited on Ar-ion-milled Magnesium Oxide (MgO)substrate are rotated 45 degree with respect to those of MgO, while the a- andb-axis of the film grown on pristine MgO substrate are parallel to those ofMgO. With photolithography and this technique, we can prepare FeSe0.3Te0.7 filmwith two kinds of orientations on the same MgO substrate, and the connectionbetween them forms a ramp at an angle about 25 degree to the substrate plane.In the planar region with either 0 degree or 45 degree orientation, we haveobserved tunneling spectra with a superconducting gap about 5 meV and 1.78 meVrespectively. However, a much larger gap about 18 meV has been observed in theramp region. Furthermore, we have also observed a small zero-bias conductancepeak (ZBCP) inside the large gap at T = 4.3K. The ZBCP becomes smaller anddisappear with increasing temperature to 7 K. The possible causes of such largegap and the ZBCP will be discussed.