d=3 Anisotropic and d=2 tJ Models: Phase Diagrams, Thermodynamic Properties, and Chemical Potential Shift

TL;DR

This study uses renormalization-group theory to explore the phase diagrams and thermodynamic properties of anisotropic d=3 and d=2 tJ models, revealing the persistence of a potential superconducting tau phase under strong anisotropy and complex magnetic structures at various doping levels.

Contribution

It provides a detailed analysis of the phase behavior and thermodynamics of anisotropic tJ models, highlighting the robustness of the tau phase and its relation to high-T_c superconductivity.

Findings

The tau phase persists even with strong anisotropy.

Complex lamellar structures emerge at low doping levels.

Chemical potential shifts indicate possible incommensurate ordering.

Abstract

The anisotropic d=3 tJ model is studied by renormalization-group theory, yielding the evolution of the system as interplane coupling is varied from the isotropic three-dimensional to quasi-two-dimensional regimes. Finite-temperature phase diagrams, chemical potential shifts, and in-plane and interplane kinetic energies and antiferromagnetic correlations are calculated for the entire range of electron densities. We find that the novel tau phase, seen in earlier studies of the isotropic d=3 tJ model, and potentially corresponding to the superconducting phase in high-T_c materials, persists even for strong anisotropy. While the tau phase appears at low temperatures at 30-35% hole doping away from <n_i>=1, at smaller hole dopings we see a complex lamellar structure of antiferromagnetic and disordered regions, with a suppressed chemical potential shift, a possible marker of incommensurate ordering in the form of microscopic stripes. An investigation of the renormalization-group flows for the isotropic two-dimensional tJ model also shows a pre-signature of the tau phase, which appears with finite transition temperatures upon addition of the smallest interplane coupling.