Phase diagram of the $t-t'-U$ chain at half filling

TL;DR

This paper explores the phase diagram of the half-filled Hubbard chain with next-nearest-neighbor hopping, identifying three distinct phases and accurately determining their boundaries using numerical methods.

Contribution

It provides a detailed numerical analysis of phase boundaries in the $t-t'-U$ chain, including the SDWI, DI, and SS phases, with precise boundary determination methods.

Findings

Identified three phases: SDWI, DI, and SS.

Accurately determined SDWI boundary via energy level crossing.

Analyzed DI-SS boundary using multiple indicators.

Abstract

We study the half filled Hubbard chain including next-nearest-neighbor hopping $t'$. The model has three phases: one insulating phase with dominant spin-density-wave correlations at large distances (SDWI), another phase with dominant spin-dimer correlations or dimerized insulator (DI), and a third one in which long distance correlations indicate singlet superconductivity (SS). The boundaries of the SDWI are accurately determined numerically through a crossing of excited energy levels equivalent to the jump in the spin Berry phase. The DI-SS boundary is studied using several indicators like correlation exponent $K_{\rho}$, Drude weight $D_{c}$, localization parameter $z_{L}$ and charge gap $\Delta_{c}$.