**Acknowledgements**

The authors wish to thank all those who have contributed to this area of research, the members of the High Temperature Superconductivity laboratory at the Institute for Physical Research, Armenian National Academy of Sciences. This work was made possible in part by a research grant from the Armenian National Science and Education Fund (ANSEF) based in New York, USA, and was supported by the RA MES State Committee of Science and Russian Foundation for Basic Research (RF) in the frames of the joint research projects SCS 15RF‐018 and RFBR 15‐ 53‐05047 accordingly.
