Thermodynamics of the planar Hubbard model

TL;DR

This study investigates the thermodynamic properties of the two-dimensional Hubbard model across various interaction strengths, revealing entropy maxima near half-filling and the emergence of a pseudogap in spin susceptibility at strong coupling.

Contribution

It provides detailed finite-temperature calculations of thermodynamic quantities in the 2D Hubbard model using the Lanczos method, highlighting new insights into entropy and pseudogap phenomena.

Findings

Entropy peaks near half-filling at low temperatures.

Pseudogap in spin susceptibility appears for U/t ≥ 8.

Charge susceptibility peaks near half-filling.

Abstract

The thermodynamic properties: specific heat, entropy, spin susceptibility $\chi_s$ and charge susceptibility $\chi_c$ are studied as a function of temperature and doping within the two-dimensional Hubbard model with various $U/t=4 - 12$. Quantities are calculated using the finite-temperature Lanczos method with additional phase-averaging for a system of $4\times 4$ sites. Results show that the entropy at low $T$ reaches a maximum near half-filling at the electron density $n \sim 1\pm 0.15$ in the whole regime of studied $U/t$. The pseudogap in $\chi_s(T)$ becomes clearly pronounced for $U/t \geq 8$ while $\chi_c$ shows a maximum close to half-filling. The relation of results to those within the t-J model and to experiments is discussed.