Nanoscale interplay of strain and doping in a high-temperature   superconductor
  The highest temperature superconductors are electronically inhomogeneous at the nanoscale, suggesting the existence of a local variable which could be harnessed to enhance the superconducting pairing. Here we report the relationship between local doping and local strain in the cuprate superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$. We use scanning tunneling microscopy to discover that the crucial oxygen dopants are periodically distributed, in correlation with local strain. Our picoscale investigation of the intra-unit-cell positions of all oxygen dopants provides essential structural input for a complete microscopic theory. 
Ilija Zeljkovic, Jouko Nieminen, Dennis Huang, Tay-Rong Chang, Yang   He, Horng-Tay Jeng, Zhijun Xu, Jinsheng Wen, Genda Gu,...
cond-mat.str-el cond-mat.mtrl-sci cond-mat.supr-con