Model evidence of a superconducting state with a full energy gap in small cuprate islands
Annica M. Black-Schaffer, Dmitri S. Golubev, Thilo Bauch, Floriana Lombardi, and Mikael Fogelström
Accepted
We investigate subdominant order parameters stabilizing at low temperatures in nano-scale high-Tc cuprate islands, motivated by the recent observation of a fully gapped state in nanosized YBa2Cu3O7-d [D. Gustafsson et al, Nature Nanotech. 8, 25 (2013)]. Using complementary quasi-classical and tight-binding Bogoliubov-de Gennes methods, we show on distinctly different properties dependent on the symmetry being dx2-y2+i s or dx2-y2+i dxy. We find that a surface-induced dx2-y2+is phase creates a global spectroscopic gap which increases with applied magnetic field, consistent with experimental observation.