Ultra-high critical current densities of superconducting YBa2Cu3O7-δ thin films in the overdoped state

The functional properties of cuprates are strongly determined by the doping state and carrier density. We present an oxygen doping study of YBa 2 Cu 3 O 7-δ (YBCO) thin films from underdoped to overdoped state, correlating the measured charge carrier density, n H , the hole doping, p , and the critical current density, J c . Our results show experimental demonstration of strong increase of J c with n H , up to Quantum Critical Point (QCP), due to an increase of the superconducting condensation energy. The ultra-high J c achieved, 90 MA cm −2 at 5 K corresponds to about a fifth of the depairing current, i.e. a value among the highest ever reported in YBCO films. The overdoped regime is confirmed by a sudden increase of n H , associated to the reconstruction of the Fermi-surface at the QCP. Overdoping YBCO opens a promising route to extend the current carrying capabilities of rare-earth barium copper oxide (REBCO) coated conductors for applications.