Berezinskii–Kosterlitz–Thouless transition in an Al superconducting nanofilm grown on GaAs by molecular beam epitaxy

Abstract

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). Nonlinear current–voltage (I–V) measurements on such a MBE-grown superconducting nanofilm show that V ∼ 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 the I–V curves 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 correct TBKT as confirmed by fitting the data to the aforementioned models. Our experimental results unequivocally show that I–V measurements alone may not allow one to determine TBKT for superconducting transition. Therefore, one should try to fit one’s results to the temperature-induced vortices/antivortices unbinding model and the dynamical scaling theory to accurately determine TBKT in a two-dimensional superconductor.