Strongly enhanced superconductivity in coupled t-J segments

The $t\text{\hspace{0.17em}⁣}\text{\hspace{0.17em}⁣}-\text{\hspace{0.17em}⁣}\text{\hspace{0.17em}⁣}J$ Hamiltonian is one of the cornerstones in the theoretical study of strongly correlated copper-oxide based materials. Using the density matrix renormalization group method we calculate the phase diagram of the one-dimensional (1D) $t\text{\hspace{0.17em}⁣}\text{\hspace{0.17em}⁣}-\text{\hspace{0.17em}⁣}\text{\hspace{0.17em}⁣}J$ chain in the presence of a periodic hopping modulation, as a prototype of coupled-segment models. While in the uniform 1D $t\text{\hspace{0.17em}⁣}\text{\hspace{0.17em}⁣}-\text{\hspace{0.17em}⁣}\text{\hspace{0.17em}⁣}J$ model near half-filling superconducting (SC) state dominates only at unphysically large values of the exchange coupling constant $J\mathrm{/}t>3$, we show that a small hopping and exchange modulation very strongly reduces the critical coupling to be as low as $J\mathrm{/}t\sim 1\mathrm{/}3$ – well within the physical regime. The phase diagram as a function of the electron filling also exhibits metallic, insulating line phases and regions of phase separation. We suggest that a SC state is easily stabilized if $t\text{\hspace{0.17em}⁣}\text{\hspace{0.17em}⁣}-\text{\hspace{0.17em}⁣}\text{\hspace{0.17em}⁣}J$ segments creating local spin-singlet pairing are coupled to each other – another example is ladder system.