Hole and electron dynamics in the triangular-lattice antiferromagnet -- interplay of frustration and spin fluctuations

TL;DR

This paper investigates the complex interplay of frustration, spin fluctuations, and electron interactions in the triangular-lattice Hubbard model, revealing incoherent electron dynamics and a fluctuation-driven metal-insulator transition.

Contribution

It introduces a fluctuation approach to analyze single-particle dynamics in the triangular-lattice antiferromagnet, highlighting the roles of magnon processes and frustration effects.

Findings

Strong fermion-magnon scattering causes incoherent electron behavior.

Finite U interactions and frustration influence magnon dispersion and electron spectra.

A fluctuation-induced first-order metal-insulator transition is identified.

Abstract

Single-particle dynamics in the 120$^{\circ}$ ordered antiferromagnetic state of the triangular-lattice Hubbard model is studied using a physically transparent fluctuation approach in terms of multiple magnon emission and absorption processes within the noncrossing approximation. Hole and electron spectral features are evaluated at intermediate $U$, and analyzed in terms of a competition between the frustration-induced direct hopping and the virtual hopping terms. Finite $U$-induced competing interactions and frustration effects contributing through the magnon dispersion are also discussed. Finite contribution to self-energy correction from long-wavelength (Goldstone) modes, together with the high density of electron scattering states in the narrow, sharp peak in the upper band, result in strong fermion-magnon scattering leading to pronounced incoherent behaviour in the electron dynamics. The fluctuation-induced first-order metal-insulator transition due to vanishing band gap is also discussed.