New phase in the one-dimensional t-J model

Strongly Enhanced Superconductivity in Coupled t-J Segments

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 obtain the phase diagram of the one-dimensional 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 the near half-filling superconducting 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∼1/3--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 superconducting state is easily stabilized if t-J segments creating local spin-singlet pairing are coupled to each other--another example is the ladder system.

Variational study of the one dimensional t-J model: a unified description of the ground state phase diagram

We find that the Gutzwiller projected Fermi sea wavefunction (GPWF) has the correct phase structure to describe the kink nature of the doped holes in the ground state of the one dimensional t-J model. We find the residual charge correlation beyond the GPWF is well described by an XXZ-type effective Hamiltonian. A Pfaffian-type variational wavefunction with only one parameter is proposed based on this observation and is found to reproduce correctly the global phase diagram and correlation functions of the one dimensional t-J model in both the Tomonaga-Luttinger regime and the Luther-Emery regime.