  Recently, Kayyalha et al. (2019 Phys. Rev. Lett. 122 047003) reported on
anomalous enhancement of the self-field critical currents, Ic(sf,T), at low
temperatures in Nb/BiSbTeSe2-nanoribbon/Nb Josephson junctions. The enhancement
was attributed to the low-energy Andreev bound states arising from winding of
the electronic wave function around the circumference of the topological
insulator BiSbTeSe2 nanoribbon. In this paper, we show that identical
enhancement in Ic(sf,T) and in the upper critical field, Bc2(T), at
approximately same reduced temperatures, were reported by several research
groups in atomically thin junctions based on a variety of Dirac-cone materials
(DCM) earlier. Our analysis shows that in all these S/DCM/S systems the
enhancement is due to a new superconducting band opening. Taking in account
that several intrinsic superconductors also exhibit the effect of new
superconducting band(s) opening when sample thickness becomes thinner than the
ground state out-of-plane coherence length, we strength our previous proposal
that there is a new phenomenon of additional superconducting band(s) opening in
atomically thin films.
