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

TL;DR

This study uses scanning tunneling microscopy to investigate the superconducting gaps and tunneling spectra of FeSe0.3Te0.7 films with different orientations, revealing a large gap and zero-bias conductance peak near the grain boundary.

Contribution

It demonstrates the fabrication of FeSe0.3Te0.7 films with controlled orientations on a single substrate and characterizes their superconducting properties at grain boundaries.

Findings

Superconducting gaps of 5 meV and 1.78 meV observed in planar regions.

A significantly larger gap of about 18 meV observed in the ramp region.

Zero-bias conductance peak (ZBCP) appears inside the large gap at low temperature.

Abstract

We used STM to study the tunneling spectra of FeSe0.3Te0.7 films with two orientations of ab-planes and the connection ramp between them. We have discovered that, using pulse laser deposition (PLD) method, the a- and b-axis of 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- and b-axis of the film grown on pristine MgO substrate are parallel to those of MgO. With photolithography and this technique, we can prepare FeSe0.3Te0.7 film with two kinds of orientations on the same MgO substrate, and the connection between 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 have observed tunneling spectra with a superconducting gap about 5 meV and 1.78 meV respectively. However, a much larger gap about 18 meV has been observed in the ramp region. Furthermore, we have also observed a small zero-bias conductance peak (ZBCP) inside the large gap at T = 4.3K. The ZBCP becomes smaller and disappear with increasing temperature to 7 K. The possible causes of such large gap and the ZBCP will be discussed.