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<p>Deconfined quantum criticality represents an exotic state of matter that is characterized by emergent symmetry and fractionalized spin excitations. However, its stabilization in frustrated quantum magnets and corresponding spectral signatures have remained elusive. Here, we investigate the spin excitation spectra of the highly frustrated <i>S</i> = 1/2 antiferromagnetic (AFM) Shastry-Sutherland model, tracing the evolution of low-energy collective modes across the transition from the Néel AFM phase to the plaquette valence bond solid (PVBS) phase. We show that the magnon bands in the AFM state exhibit opposite chiralities and a non-relativistic splitting, arising from the altermagnetic nature as dictated by the underlying lattice symmetry. We further uncover two remarkable low-lying excitations: a Higgs mode in the longitudinal excitation channel and an <i>S</i> = 0 excitation with vanishing spectral weight. Upon approaching the AFM-to-PVBS transition, both these modes soften concurrently with the lowest-energy triplet and singlet modes of the PVBS state. The energy gap closing of the Higgs mode, together with the nearly degenerate velocities of <i>S</i> = 1 and <i>S</i> = 0 excitations, provides direct spectral evidence that the AFM-to-PVBS transition is proximate to a deconfined quantum critical point with emergent <i>O</i>(4) symmetry. Our results help clarify the spectral fingerprint of deconfined quantum criticality and advance the understanding of symmetry-enhanced quantum phase transitions more broadly.</p>

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Emergent symmetry and deconfined quantum criticality in the Shastry-Sutherland model: A spin excitation diagnosis

  • 期刊论文

  • 发表日期：

    2026年6月24日

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  • Hongyu Chen,
  • Guijing Duan,
  • Yi Cui,
  • Weiqiang Yu,
  • Z. Y. Xie,
  • Changle Liu,
  • Rong Yu

摘要

Deconfined quantum criticality represents an exotic state of matter that is characterized by emergent symmetry and fractionalized spin excitations. However, its stabilization in frustrated quantum magnets and corresponding spectral signatures have remained elusive. Here, we investigate the spin excitation spectra of the highly frustrated S = 1/2 antiferromagnetic (AFM) Shastry-Sutherland model, tracing the evolution of low-energy collective modes across the transition from the Néel AFM phase to the plaquette valence bond solid (PVBS) phase. We show that the magnon bands in the AFM state exhibit opposite chiralities and a non-relativistic splitting, arising from the altermagnetic nature as dictated by the underlying lattice symmetry. We further uncover two remarkable low-lying excitations: a Higgs mode in the longitudinal excitation channel and an S = 0 excitation with vanishing spectral weight. Upon approaching the AFM-to-PVBS transition, both these modes soften concurrently with the lowest-energy triplet and singlet modes of the PVBS state. The energy gap closing of the Higgs mode, together with the nearly degenerate velocities of S = 1 and S = 0 excitations, provides direct spectral evidence that the AFM-to-PVBS transition is proximate to a deconfined quantum critical point with emergent O(4) symmetry. Our results help clarify the spectral fingerprint of deconfined quantum criticality and advance the understanding of symmetry-enhanced quantum phase transitions more broadly.