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arXiv · 2604.24868

Dynamical dimer structure factor of the triangular $S=1/2$ Heisenberg antiferromagnet

Markus Drescher·Laurens Vanderstraeten·Roderich Moessner·Frank Pollmann·Johannes Knolle
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Abstract

The dynamical dimer structure factor is an observable probing spin-singlet excitations of quantum magnets distinct from those commonly studied by the spin structure factor. We report the dimer response for the extended spin-$1/2$ antiferromagnetic Heisenberg model on the triangular lattice using large-scale GPU-accelerated matrix-product-state simulations. We investigate the ordered phases with $120^\circ$ coplanar, collinear stripe, and tetrahedral spin order, as well as candidate quantum spin-liquid (QSL) regimes, comprising an expected gapless $U(1)$ Dirac QSL and a chiral QSL at finite spin-scalar-chirality coupling. In the ordered phases, we find low-energy modes below the onset of the two-magnon continuum illustrating avoided quasiparticle decay. Within the candidate gapless QSL, we observe absolute dispersion minima at momenta of half the Brillouin zone corners, $X\equiv K/2$, in agreement with field-theory predictions that singlet monopole excitations of the $U(1)$ Dirac spin liquid become gapless at these points. Thus, the high-resolution dynamical dimer response provides support for a $U(1)$ Dirac QSL with singlet monopole excitations.

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Markus Drescher, Laurens Vanderstraeten, Roderich Moessner, Frank Pollmann, Johannes Knolle. 2026-04-27. Dynamical dimer structure factor of the triangular $S=1/2$ Heisenberg antiferromagnet. https://arxiv.org/abs/2604.24868

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