Qiyang Chen

Mixed-State Hall Effect in HgBa 2 CaCu 2 O 6+δ Thin Films with Columnar Defects

The mixed state Hall effect has been studied in high quality HgBa2CaCu2O6+δ thin films while the pinning strength is modified by the irraddition of columnar defects. It has been shown that the pinning strength can be significantly improved by columnar defects. The sign reversal in Hall resistivity is found to be nearly independent of pinning while the scaling behavior between Hall resistivity (ρxy) and longitudinal resistivity (ρxx) is influenced by pinning. The exponent β in the scaling law βxy ∼ βxyβ decrease from 1.8 ± 0.1 to 1.5 ± 0.1 as pinning is enhanced. This results suggest that the sign reversal and the scaling are unrelated, and pinning is not the mechanism of the sign reversal.

PrBa2(Cu0.8Al0.2)3O7 Thin Film Surface Smoothing by Ar‐Cluster Ion Beam Bombardment

Al doped PrBa2Cu 3O7 epitaxial thin film is an excellent insulating material for oxide superconducting junction application. The surface of such films grown at high temperature is usually very rough and requires smoothing during device fabrication. A gas cluster ion beam is a good tool for smoothing the surface down to the sub‐nanometer level. In this paper, PrBa2(Cu0.8Al0.2)3O7 thin films of different thickness grown by Pulsed Laser Deposition (PLD) were irradiated with a 20 keV Ar‐cluster ion beam. The average size of the Ar‐clusters was about 3000 atoms per cluster. A film thickness varying from 48nm to 920 nm with corresponding initial roughness of 2 nm to 10 nm was studied. The roughness was gradually reduced with increasing cluster ion dosage, reaching an ultimate of 0.7 nm. For a sample of average sputtering yield, surface damage and the annealing effect after smoothing were also studied.