Superconducting and correlated phases of an effective Hubbard model on the BCC lattice

TL;DR

This paper explores the complex electronic phases of an effective Hubbard model on the BCC lattice, revealing insights into superconductivity, magnetism, and Mott insulators relevant to fulleride materials.

Contribution

It introduces a combined theoretical approach to analyze superconducting and correlated phases in a Hubbard model on the BCC lattice, highlighting phase transitions and phase competition.

Findings

First-order transition between normal and superconducting phases.

Identification of phase boundaries among Fermi-liquid, antiferromagnetic, and Mott insulator phases.

Unified phase diagram capturing interplay of itinerancy, magnetism, and localization.

Abstract

We investigate the electronic phases of an effective Hubbard model on the body-centered-cubic lattice, motivated by alkali-doped fulleride molecular solids. The model incorporates renormalized on-site interactions and an effective inverted Hund's coupling originating from electron-phonon interactions. To access complementary interaction regimes, we employ two theoretical approaches. In the intermediate-coupling regime, the on-site repulsive interaction is approximated by a long-range interaction in momentum space, yielding an exactly solvable Hatsugai-Kohmoto model supplemented by a BCS-type pairing term. Within this framework, we analyze the superconducting instability and demonstrate a first-order normal-superconducting phase transition, characterized by a discontinuous jump of the order parameter. In the strong-coupling regime, where pairing fluctuations are suppressed, we apply the spin rotationally invariant slave-boson formalism to map out the temperature-interaction phase diagram. This analysis reveals first-order transitions between a Fermi-liquid phase, an antiferromagnetic phase, and a Mott insulating phase, with a narrow intermediate region where all three phases compete. The resulting phase diagram captures the interplay of itinerancy, magnetic order, and Mott localization in three dimensions and provides a unified perspective on superconducting and correlation-driven phenomena in fulleride-inspired lattice systems.