LAUSR

We have performed extensive transport experiments on a 4-nm-thick aluminum (Al) superconducting film grown on a GaAs substrate by molecular beam epitaxy (MBE). Non-linear current-voltage (I-V) measurements on such a MBE-grown superconducting nanofilm show thatV~I3, which is evidence for the Berezinskii-Kosterlitz-Thouless (BKT) transition, both in the low-voltage (TBKT≈ 1.97 K) and high-voltage regions (TBKT≈ 2.17 K). In order to further study the two regions where theI-Vcurves are BKT-like, our experimental data are fitted to the temperature-induced vortices/antivortices unbinding model as well as the dynamical scaling theory. It is found that the transition temperature obtained in the high-voltage region is the correctTBKTas confirmed by fitting the data to the aforementioned models. Our experimental results unequivocally show thatI-Vmeasurements alone may not allow one to determineTBKTfor superconducting transition. Therefore, one should try to fit one's data to the temperature-induced vortices/antivortices unbinding model and the dynamical scaling theory to accurately measureTBKTin a two-dimensional superconductor.