Kondo versus Fano in superconducting artificial high-Tc heterostructures

Abstract

Recently, the quest for high-Tc superconductivity has evolved from the trial-and-error methodology to the growth of nanostructured artificial high-Tc superlattices (AHTS) with tailor-made superconducting functional properties by quantum design. Superlattices are composed of nanoscale superconducting units of modulation doped Mott insulator La2CuO4 with thickness L intercalated by metallic overdoped La1.55Sr0.45CuO4 and period d. Quantum design based on the multi-gap Bogoliubov theory including spin-orbit coupling (SOC). has been employed for prediction of the amplification of the critical temperature as a function of the conformational parameter L/d. At the top of the superconducting dome, at the magic ratio L/d=2/3, the heterostructures are tuned at the Fano-Feshbach resonance and the normal phase exhibits the Planckian T-linear resistivity. Here, we report experimental evidence that the Kondo proximity effect competes with the Fano-Feshbach resonance suppressing Tc on both sides of the superconducting dome. The Kondo proximity effect is expected in electrical resistance of AHTS nanoscale heterostructures following a Kondo universal scaling obtained by numerical renormalization group theory. We show the vanishing Kondo temperature TK and Kondo scattering amplitude R0K at L/d=2/3, while TK and R0K increase on the underdoped (L/d>2/3) and overdoped (L/d<2/3) side of the superconducting dome.