Excitations and dynamical structure factor of J1-J2 spin-3/2 and spin-5/2 Heisenberg spin chains
Aman Sharma (École Polytechnique Fédérale de Lausanne, Student TU Delft)
Mithilesh Nayak (University of Fribourg, The University of Tennessee Knoxville)
Natalia Chepiga (Kavli institute of nanoscience Delft, TU Delft - Applied Sciences)
Frédéric Mila (École Polytechnique Fédérale de Lausanne)
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Abstract
We study the dynamical structure factor of the frustrated spin-3/2 J1-J2 Heisenberg chains, with particular focus on the partially dimerized phase that emerges between two Kosterlitz-Thouless transitions. Using a valence bond solid Ansatz corroborated by density-matrix renormalization-group simulations, we investigate the nature of magnon and spinon excitations through the single-mode approximation. We show that the magnon develops an incommensurate dispersion at J2 ≈ 0.32J1, while the spinons, viewed as domain walls between degenerate valence bond solid states, become incommensurate at J2 ≈ 0.4J1 beyond the Lifshitz point (J2 ≈ 0.388J1). The dynamical structure factor exhibits rich spectral features shaped by the interplay between these excitations, with magnons appearing as resonances embedded in the spinon continuum. The spinon gap shows a nonmonotonic behavior, reaching a peak near the center of the partially dimerized phase and closing at the boundaries, suggesting the appearance of a floating phase as a result of the condensation of incommensurate spinons. Comparative analysis with the spin-5/2 case confirms the universality of these phenomena across half-integer higher-spin systems. Our results provide detailed insight into how fractionalization and incommensurate condensation govern the spectral properties of frustrated spin chains, offering a unified picture across different spin magnitudes.