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.