  Extensive investigations on the Moir\'e magic-angle have been conducted in
twisted bilayer graphene, unlocking the mystery of unconventional
superconductivity and insulating states. In analog to magic angle, here we
demonstrate the new concept of magic-strain in graphene systems by judiciously
tailoring mechanical relaxation (stretch and compression) which is easier to
implement in practice. We elucidate the interplay of strain-induced effects and
delve into the resulting unconventional superconductivity or
semimetal-insulator transition in relaxation-strained graphene, going beyond
the traditional twisting approach. Our findings reveal how relaxation strain
can trigger superconducting transitions (with an ultra-flat band at the Fermi
level) or the semimetal-insulator transition (with a gap opening at the $K$
point of $0.39\rm{~eV}$) in both monolayer and bilayer graphene. These
discoveries open up a new branch for correlated phenomena and provide deeper
insights into the underlying physics of superconductors, which positions
graphene as a highly tunable platform for novel electronic applications.
