Emergent Quasiparticles \& Field-Tuned RIXS Spectra in a Trimerized Spin-1/2 Chain

TL;DR

This study uses advanced numerical methods to analyze RIXS spectra in a trimerized spin-1/2 chain, revealing emergent quasiparticles, fractionalized excitations, and field-tuned spectral evolution with potential for Bose condensation.

Contribution

It introduces a detailed theoretical analysis of RIXS spectra in a trimerized chain, highlighting emergent quasiparticles and the effects of magnetic fields on spectral features.

Findings

Emergent gapless modes governed by trimer periodicity.

Identification of fractionalized spinons and composite quasiparticles.

Field-induced evolution of spectra toward spin-polarized and gapless excitations.

Abstract

We investigate spin-flip excitations in the spin-1/2 trimer chain $\rm{Cu_3(P_2O_6OH)_2}$, featuring an antiferromagnetic exchange motif $J_1$-$J_1$-$J_2$ with $J_1 < J_2$. Using density matrix renormalization group (DMRG) simulations, we demonstrate that single-spin-flip processes induced by resonant inelastic X-ray scattering (RIXS) generate emergent gapless modes governed by the underlying trimer periodicity alongside distinct high-energy excitations. By combining exact diagonalization and real-space renormalization group (RG) techniques, we attribute these features to fractionalized spinons and composite quasiparticles arising from one- and two-trimer excitations. Furthermore, we show that multi-spin RIXS excitations yield experimentally distinguishable spectral signatures of composite modes absent in single-spin-flip spectra. At the field-induced 1/3 magnetization plateau, single-spin-flip RIXS spectra evolves with the magnetic field to favor spin-polarized composite quasiparticles. This trend culminates in a gapless spectrum of spin-1 excitations beyond the plateau, paving the way for field-tuned Bose condensation of composite modes.