Gapless spin-liquid phase in the kagome spin-1/2 Heisenberg antiferromagnet

TL;DR

This study investigates the ground state of the spin-1/2 kagome Heisenberg antiferromagnet, providing evidence for a gapless U(1) Dirac spin liquid with energy estimates consistent with DMRG results, using advanced Monte Carlo methods.

Contribution

It demonstrates that a gapless U(1) Dirac spin liquid is competitive with gapped Z2 states, using improved Monte Carlo techniques and finite-size extrapolation.

Findings

Identifies a gapless U(1) Dirac spin liquid as a viable ground state.

Obtains energy per site E/J=-0.4365(2), consistent with DMRG.

Shows finite-size energies are lower than DMRG estimates.

Abstract

We study the energy and the static spin structure factor of the ground state of the spin-1/2 quantum Heisenberg antiferromagnetic model on the kagome lattice. By the iterative application of a few Lanczos steps on accurate projected fermionic wave functions and the Green's function Monte Carlo technique, we find that a gapless (algebraic) U(1) Dirac spin liquid is competitive with previously proposed gapped (topological) Z2 spin liquids. By performing a finite-size extrapolation of the ground-state energy, we obtain an energy per site E/J=-0.4365(2), which is equal, within three error bars, to the estimates given by the density-matrix renormalization group (DMRG). Our estimate is obtained for a translationally invariant system, and, therefore, does not suffer from boundary effects, like in DMRG. Moreover, on finite toric clusters at the pure variational level, our energies are lower compared to those from DMRG calculations.