Collective spin excitations in a quantum spin ladder probed by high-resolution Resonant Inelastic X-ray Scattering

TL;DR

This study uses high-resolution RIXS to probe magnetic excitations in a quantum spin ladder, revealing collective spin excitations and a two-triplon energy gap, with results supported by Hubbard model calculations.

Contribution

It demonstrates RIXS's effectiveness in detecting collective spin excitations in a quantum spin-liquid state, providing new insights beyond neutron scattering.

Findings

RIXS couples to collective spin excitations with high sensitivity.

Two-triplon energy gap measured at 100±30 meV.

Results supported by Hubbard model calculations.

Abstract

We investigate magnetic excitations in the spin-ladder compound Sr$_{14}$Cu$_{24}$O$_{41}$ using high-resolution Cu $L_3$-edge Resonant Inelastic X-ray Scattering (RIXS). Our findings demonstrate that RIXS couples to collective spin excitations from a quantum spin-liquid ground state. In contrast to Inelastic Neutron Scattering (INS), the RIXS cross section changes only moderately over the entire Brillouin Zone (BZ), revealing a high sensitivity also at small momentum transfers. The two-triplon energy gap is found to be $100\pm 30$ meV. Our results are supported by calculations within an effective Hubbard model for a finite-size cluster.