"High TC superconductivity in interacting quasi-2D sheets at oxide interfaces"

Speaker: Dr Daniele Di Castro - Proponent: G.M. De Luca - A. Rubano

High Tc superconductivity has been recently revealed at the interface between CaCuO2 and SrTiO3 in CaCuO2/SrTiO3 (CCO/STO) heterostructures and superlattices. STEM/EELS measurements have demonstrated that, in these systems, the hole doping is obtained via oxygen ions uptaking in the Ca plane of CaCuO2 (CCO) at the interface with the TiO2 plane of SrTiO3 (STO), allowing a Tc of about 40 K in the heterostructure and about 50 K in the superlattice.

A detailed hole doping spatial profile has been obtained by STEM/EELS at the O K edge: the hole concentration decays rapidly by moving within the CCO far from the interface with STO, and becomes almost negligible after about two CCO unit cells (two CuO2 planes). So that, the inner CuO2 planes are strongly underdoped and probably undoped and antiferromagnetic. Basing on these results obtained in CCO/STO systems, we make a comparison among the superconducting properties of different cuprate-based oxide heterostructures and superlattices. Throughout this comparison, we propose a phenomenological explanation of the behavior of the Tc by introducing two kinds of interactions between the superconducting quasi-2D sheets.

This interpretation can be extended to standard multilayered high Tc cuprates, which can be schematized as a sequence of natural interfaces between an insulating block with "infinite layers" structure, as CCO, and a charge reservoir block.