Thermodynamic properties and thermal correlation lengths of a Hubbard model with bond-charge interaction

We investigate the thermodynamics of a one-dimensional Hubbard model with bond-charge interaction X using the transfer-matrix renormalization-group method. Numerical results for various quantities such as spin and charge susceptibilities, particle densities, specific heat, and thermal correlation lengths are presented and discussed. We compare our data also to results for the exactly solvable case $X/t=1\mathrm{}$ as well as to bosonization results for weak coupling $X/t\ll 1,$ which shows excellent agreement. We confirm the existence of a Tomonaga-Luttinger and a Luther-Emery liquid phase, in agreement with previous studies at zero temperature. Thermal singlet-pair-correlation lengths are shown to dominate density and spin correlations for finite temperatures in certain parameter regimes.