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Title: Fractional and composite excitations of antiferromagnetic quantum spin trimer chains

Using quantum Monte Carlo, exact diagonalization, and perturbation theory, we study the spectrum of theS = 1/2 antiferromagnetic Heisenberg trimer chain by varying the ratiog = J2/J1of the intertrimer and intratrimer coupling strengths. The doublet ground states of trimers form effective interactingS = 1/2 degrees of freedom described by a Heisenberg chain. Therefore, the conventional two-spinon continuum of width ∝ J1wheng = 1 evolves into to a similar continuum of width ∝ J2wheng → 0. The intermediate-energy and high-energy modes are termeddoublonsandquartonswhich fractionalize with increasinggto form the conventional spinon continuum. In particular, atg ≈ 0.716, the gap between the low-energy spinon branch and the high-energy band with mixed doublons, quartons, and spinons closes. These features should be observable in inelastic neutron scattering experiments if a quasi-one-dimensional quantum magnet with the linear trimer structure andJ2 < J1can be identified. Our results may open a window for exploring the high-energy fractional excitations.

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Publication Date:
Journal Name:
npj Quantum Materials
Nature Publishing Group
Sponsoring Org:
National Science Foundation
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