Fractional and composite excitations of antiferromagnetic quantum spin trimer chains
Sandvik, Anders W.
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Citation (published version)J.-.Q. Cheng, J. Li, Z. Xiong, H.-.Q. Wu, A.W. Sandvik, D.-.X. Yao. 2022. "Fractional and composite excitations of antiferromagnetic quantum spin trimer chains." npj Quantum Materials, Volume 7, Issue 1, https://doi.org/10.1038/s41535-021-00416-4
Using quantum Monte Carlo, exact diagonalization, and perturbation theory, we study the spectrum of the S = 1/2 antiferromagnetic Heisenberg trimer chain by varying the ratio g = J2/J1 of the intertrimer and intratrimer coupling strengths. The doublet ground states of trimers form effective interacting S = 1/2 degrees of freedom described by a Heisenberg chain. Therefore, the conventional two-spinon continuum of width ∝ J1 when g = 1 evolves into to a similar continuum of width ∝ J2 when g → 0. The intermediate-energy and high-energy modes are termed doublons and quartons which fractionalize with increasing g to form the conventional spinon continuum. In particular, at g ≈ 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 and J2 < J1 can be identified. Our results may open a window for exploring the high-energy fractional excitations.
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