The emergence of superconductivity in doped insulators such as cuprates and pnictides coincides with their doping-driven insulator–metal transitions. Above the critical doping threshold, a metallic state sets in at high temperatures, while superconductivity sets in at low temperatures. An unanswered question is whether the formation of Cooper pairsin a well-established metal will inevitably transform the host material into a superconductor, as manifested by a resistance drop. Here, this question is addressed by investigating the electrical transport in nanoscale rings (full loops) and half loops manufactured from heavily boron-doped diamond. It is shown that in contrast to the diamond half-loops (DHLs) exhibiting a metal–superconductor transition, the diamond nanorings (DNRs) demonstrate a sharp resistance increase up to 430% and a giant negative “magnetoresistance” below the superconducting transition temperature of the starting material. The finding of the unconventional giant negative “magnetoresistance”, as distinct from existing categories of magnetoresistance, that is, the conventional giant magnetoresistance in magnetic multilayers, the colossal magnetoresistance in perovskites, and the geometric magnetoresistance in semiconductor–metal hybrids, reveals the transformation of the DNRs from metals to bosonic semiconductors upon the formation of Cooper pairs. DNRs like these could be used to manipulate Cooper pairs in superconducting quantum devices.
Bibliographical noteFunding Information:
The authors thank Johan Vanacken for valuable discussions and Tomoki Oki, Naoki Ikeda, and Sawabe Yumiko for technical assistance. R.Z. thanks the Ph.D. studentship funded through the Bolashak International Scholarship programme of the Republic of Kazakhstan. X.K. acknowledges the National Natural Science Foundation of China (12074017) and the National Natural Science Fund for Innovative Research Groups of China (51621003). The work at NIMS was supported by JSPS KAKENHI (20H02212). L.L. acknowledges the FWO (Research Foundation‐Flanders) for a research fellowship (12V4422N). Y.L. thanks the National Natural Science Foundation of China (11904411).
© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.
- bosonic semiconductors
- diamond nanorings
- diamond nanowires
- trapping of Cooper pairs
- unconventional giant magnetoresistance