Magnetic, thermodynamic, and dynamical properties of the three-dimensional fermionic Hubbard model: A comprehensive Monte Carlo study

TL;DR

This comprehensive Monte Carlo study investigates the finite-temperature phase diagram of the three-dimensional fermionic Hubbard model, revealing detailed thermodynamic and magnetic properties, including the Nel transition and metal-insulator crossover, with unprecedented system sizes.

Contribution

The paper introduces new techniques for calculating thermal entropy and the U-derivative of double occupancy, enabling precise determination of phase boundaries in the Hubbard model.

Findings

Accurate Nel transition temperatures up to 20^3 system size.

Identification of the metal-insulator crossover boundary.

Persistence of antiferromagnetic order at finite doping.

Abstract

The interplay between quantum and thermal fluctuations can induce rich phenomena at finite temperatures in strongly correlated fermion systems. Here we report a {\it numerically exact} auxiliary-field quantum Monte Carlo (AFQMC) study for the finite-temperature properties of three-dimensional repulsive Hubbard model at half filling. We concentrate on the complete temperature-interaction strength phase diagram of the model, which contains the low-temperature antiferromagnetic (AFM) long-range ordered phase and metal-insulator crossover (MIC) in the paramagnetic phase. Enabling access to unprecedented system sizes up to $20^3$, we achieve highly accurate results of the N\'{e}el transition temperature for representative values of on-site interaction $U$ via finite-size analysis of AFM structure factor. To quantitatively characterize the MIC above the N\'{e}el transition, we have developed fully new techniques allowing to compute the thermal entropy versus $U$ at fixed temperature and to directly calculate the $U$-derivative of double occupancy in AFQMC simulations. Then combining variously thermodynamic and dynamical observables, we establish an efficient scheme to precisely determine the boundaries for the MIC by cross-checking different observables. We also demonstrate the temperature dependence of many commonly used observables. Away from half filling, we explore the behavior of the sign problem and AFM spin correlation versus hole doping, and demonstrate the persistance of N\'{e}el AFM ordered phase to finite doping with limited results.