Gapless spin-liquid phase in an extended spin 1/2 triangular Heisenberg model

TL;DR

This study demonstrates that adding a weak next-nearest-neighbor interaction to a spin-1/2 triangular Heisenberg model stabilizes a gapless quantum spin-liquid phase with algebraic correlations, revealing an unconventional critical phase.

Contribution

It introduces a novel extended model showing a stable algebraic spin-liquid phase, highlighting the role of next-nearest-neighbor interactions in quantum magnetism.

Findings

Identification of a gapless spin-liquid phase stabilized by next-nearest-neighbor interactions.

Observation of algebraic decay of correlations at the critical point and within the spin-liquid phase.

Detection of small excitation energies constraining the nature of the algebraic spin liquid.

Abstract

We numerically study the Heisenberg models on triangular lattices by extending it from the simplest equilateral lattice with only the nearest-neighbor exchange interaction. We show that, by including an additional weak next-nearest-neighbor interaction, a quantum spin-liquid phase is stabilized against the antiferromagnetic order. The spin gap (triplet excitation gap) and spin correlation at long distances decay algebraically with increasing system size at the critical point between the antiferromagnetic phase and the spin-liquid phase. This algebraic behavior continues in the spin-liquid phase as well, indicating the presence of an unconventional critical (algebraic spin-liquid) phase characterized by the dynamical and anomalous critical exponents $z+\eta\sim1$. Unusually small triplet and singlet excitation energies found in extended points of the Brillouin zone impose constraints on this algebraic spin liquid.