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arXiv · 2608.05277

Superconducting and charge-ordered phases from Dirac quantum spin liquids on the triangular lattice

Andreas Feuerpfeil·Ronny Thomale·Subir Sachdev·Pietro M. Bonetti
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Abstract

Triangular-lattice quantum spin-liquid insulators are observed to undergo transitions to superconductivity under pressure or doping, and exhibit enhanced terahertz conductivity when driven by mid-infrared light. We present a general theoretical framework for the emergence of superconducting and charge-ordered phases from a U(1) Dirac spin liquid with fermionic spinons, as well as from its gapped $\mathbb{Z}_2$ and chiral descendants. Numerical studies have provided substantial evidence for these spin-liquid states. The spin-liquid phase hosts fractionalized Dirac spinons coupled to an emergent gauge field, whereas the superconducting and charge-ordered phases are conventional, with neither fractionalized excitations nor emergent gauge dynamics. The transition between these phases is driven by the Higgs condensation of spinless charge-$e$ bosonic chargons (``doublons'' and ``holons''). We show that the projective symmetry group of the Dirac spinons uniquely determines the symmetry and dispersion of the chargons, allowing us to construct an effective low-energy theory near the chargon band minima. Gauge-invariant composites of the chargon Higgs fields provide the order parameters characterizing the phases. The resulting phase diagram contains a rich variety of ordered states, including $d+id$ superconductivity, charge-density waves, bond-density waves, and pair-density waves.

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Andreas Feuerpfeil, Ronny Thomale, Subir Sachdev, Pietro M. Bonetti. 2026-08-05. Superconducting and charge-ordered phases from Dirac quantum spin liquids on the triangular lattice. https://arxiv.org/abs/2608.05277

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