TRANSPORT MEASUREMENT AND SCANNING IMAGING ON TWO DIMENSIONAL MATERIALS

Abstract

𝑁𝑏𝑆𝑒2 is a type II superconductor with its superconductivity preserved from bulk all the way down to one atomic layer. We used both electrochemical and mechanical exfoliation to fabricate twisted atomic-layer 𝑁𝑏𝑆𝑒2 devices with high quality. In those devices, we observed exotic features which are not expected in pristine isotropic superconductors. The critical current of such twisted 𝑁𝑏𝑆𝑒2 showed oscillatory behavior under out-of-plane magnetic field, which we attributed to the formation of Josephson junction array aided by moiré superlattice. To uncover the microscopic picture of vortex configuration in twisted 𝑁𝑏𝑆𝑒2, we developed a new scanning probe measurement technique based on the single electron transistor. We have achieved ~100 𝑛𝑚 spatial resolution and ~30 𝜇𝑉 voltage sensitivity in our setup. We demonstrated the operability and validity of this scanning SET probe by approaching 2D 𝑀𝑜𝑆2 and measuring its surface potential and electronic compressibility.