Strongly enhanced superconductivity in coupled t-J segments

TL;DR

This paper demonstrates that periodic modulation of hopping in a 1D $t$-$J$ chain significantly enhances superconductivity, making it stable at realistic coupling strengths and revealing complex phase behavior.

Contribution

The study shows that coupling $t$-$J$ segments with hopping modulation strongly promotes superconductivity at lower coupling values than in uniform models.

Findings

Superconductivity is stabilized at $J/t \\sim 1/3$ with modulation.

Phase diagram includes metallic, insulating, and phase-separated regions.

Hopping modulation reduces the critical coupling for superconductivity.

Abstract

The $t\!\!-\!\!J$ 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) $t\!\!-\!\!J$ chain in the presence of a periodic hopping modulation, as a prototype of coupled-segment models. While in the uniform 1D $t\!\!-\!\!J$ model near half-filling superconducting (SC) state dominates only at unphysically large values of the exchange coupling constant $J/t>3$, we show that a small hopping and exchange modulation very strongly reduces the critical coupling to be as low as $J/t\sim1/3$ -- 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 $t\!\!-\!\!J$ segments creating local spin-singlet pairing are coupled to each other -- another example is ladder system.