Competing phases of the Hubbard model on a triangular lattice -- insights from the entropy

TL;DR

This study uses the ladder dual-fermion approach to explore the phase diagram of the Hubbard model on a triangular lattice, revealing various phases influenced by frustration and correlations, and highlights the role of entropy in understanding experimental phenomena.

Contribution

It demonstrates that the Hubbard model on frustrated lattices can capture a wide range of experimentally observed phases and emphasizes the importance of entropy in analyzing these systems.

Findings

Identification of multiple phases including paramagnetic metal and insulator, Mott insulator with 120° antiferromagnetic order, and possible spin liquid.

Entropy considerations explain features like large thermopower in Na_xCoO_2·yH_2O.

The phase diagram aligns with experimental observations in frustrated electronic systems.

Abstract

Based on the ladder dual-fermion approach, we present a comprehensive study of the phases of the isotropic Hubbard model on the triangular lattice. We find a rich phase diagram containing most of the phases that have already been experimentally observed in systems where the interplay between geometric frustration and electronic correlations is important: paramagnetic metal, paramagnetic insulator, Mott-insulator with $120^{\circ}$ antiferromagnetic and a non-magnetic insulating state, i.e. possibly a spin liquid state. This establishes that the Hubbard model on frustrated lattices can serve as a minimal model to address the intricate interplay of frustration and correlation. We also show that entropic considerations can be successfully used for understanding many striking features of the triangular systems, such as the large thermopower found in Na$_{x}$CoO$_{2}\cdot$$y$H$_{2}$O.