Networks of superconducting nano-puddles in 1/8 doped YBa2Cu3O6.5 + y controlled by thermal manipulation

Abstract

While it is known that the nature and the arrangement of defects in complex oxides have an impact on the material functionalities, little is known about control of superconductivity by oxygen interstitial organization in cuprates. Here we report direct compelling evidence for the control of T _c by manipulation of the superconducting granular networks of nanoscale puddles, made of ordered oxygen stripes, in a single crystal of YBa _2 Cu _3 O _6.5 + _y with average formal hole doping p close to 1/8. Upon thermal treatments we were able to switch from a first network of oxygen defect striped puddles with OVIII modulation ( q _OVIII ( a *) = ( h + 3/8, k , 0) and q _OVIII ( a *) = ( h + 5/8, k , 0)) to a second network characterized by OXVI modulation ( q _OXVI (a*) = ( h + 7/16, k, 0) and q ox-VI(a*) = ( h + 9/16, k , 0)) and finally to a third network with puddles of OV periodicity ( q _OV ( a *) = (4/10, 1, 0) and q _OV ( a *) = (6/10, 1, 0)). We map the microscopic spatial evolution of the out of plane OVIII, OXVI and OV puddle nano-size distribution via scanning micro-diffraction measurements. In particular, we calculated the number of oxygen chains ( n ) and the charge density (hole concentration p ) inside each puddle, analyzing areas of 160 × 80 μ m ^2 , and recording 12 800 diffraction patterns to reconstruct each spatial map. The high spatial inhomogeneity shown by all the reconstructed spatial maps reflects the intrinsic granular structure that characterizes cuprates and iron chalcogenides, disclosing the presence of several complex networks of coexisting superconducting domains with different lattice modulations, charge densities and gaps as in the proposed multi-gap scenario called superstripes.

Keywords

• phase separation
• inhomogeneity
• cuprates
• high temperature superconductivity
• complex materials