Strain and proximity effect in (La,Sr)2CuO4 based superconducting superlattices.

Abstract

Controlled variations of the in-plane Cu-O bond length and interlayer proximity coupling have been produced in laser-ablated superlattices containing superconducting ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4}$ (LSCO). In LSCO/${\mathrm{Sm}}_{2}$${\mathrm{CuO}}_{4}$ strained superlattices, the in-plane lattice constant a of the LSCO layers is increased and the transition temperature (${\mathit{T}}_{\mathit{c}}$) is decreased. We estimate the effective pressure to be -8 GPa by comparing with LSCO/${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$ unstrained superlattices. We conclude the in-plane Cu-O bond length is an important factor controlling ${\mathit{T}}_{\mathit{c}}$. For LSCO/overdoped-${\mathrm{La}}_{1.65}$${\mathrm{Sr}}_{0.35}$${\mathrm{CuO}}_{4}$ (metallic) superlattices, a proximity-induced coherence length of 50 \AA{} is calculated for the overdoped material using the de Gennes--Werthamer theory, from the ${\mathit{T}}_{\mathit{c}}$ dependence on individual layer thickness.