Crossover of high-energy spin fluctuations from collective triplons to localized magnetic excitations in Sr&lt;sub&gt;14−x&lt;/sub&gt;Ca&lt;sub&gt;x&lt;/sub&gt;Cu&lt;sub&gt;24&lt;/sub&gt;O&lt;sub&gt;41&lt;/sub&gt; ladders

Tseng, Y.; Thomas, J.; Zhang, W.; Paris, E.; Puphal, P.; Bag, R.; Deng, G.; Asmara, T.C.; Strocov, V.N.; Singh, S.; Pomjakushina, E.; Kumar, U.; Nocera, A.; Rønnow, H.M.; Johnston, S.; Schmitt, T.

doi:10.1038/s41535-022-00502-1

Crossover of high-energy spin fluctuations from collective triplons to localized magnetic excitations in Sr_14−xCa_xCu₂₄O₄₁ ladders

Tseng Y, Thomas J, Zhang W, Paris E, Puphal P, Bag R, Deng G, Asmara TC, Strocov VN, Singh S, Pomjakushina E, Kumar U, Nocera A, Rønnow HM, Johnston S & Schmitt T

Citation

Tseng, Y., Thomas, J., Zhang, W., Paris, E., Puphal, P., Bag, R., … Schmitt, T. (2022). Crossover of high-energy spin fluctuations from collective triplons to localized magnetic excitations in Sr_14−xCa_xCu₂₄O₄₁ ladders. npj Quantum Materials, 7, 92 (9 pp.). https://doi.org/10.1038/s41535-022-00502-1

Persistent URL https://www.dora.lib4ri.ch/psi/islandora/object/psi:45357

We studied the magnetic excitations in the quasi-one-dimensional (q-1D) ladder subsystem of Sr_14−xCa_xCu₂₄O₄₁ (SCCO) using Cu L₃-edge resonant inelastic X-ray scattering (RIXS). By comparing momentum-resolved RIXS spectra with high (x = 12.2) and without (x = 0) Ca content, we track the evolution of the magnetic excitations from collective two-triplon (2 T) excitations (x = 0) to weakly-dispersive gapped modes at an energy of 280 meV (x = 12.2). Density matrix renormalization group (DMRG) calculations of the RIXS response in the doped ladders suggest that the flat magnetic dispersion and damped excitation profile observed at x = 12.2 originates from enhanced hole localization. This interpretation is supported by polarization-dependent RIXS measurements, where we disentangle the spin-conserving ΔS = 0 scattering from the predominant ΔS = 1 spin-flip signal in the RIXS spectra. The results show that the low-energy weight in the ΔS = 0 channel is depleted when Sr is replaced by Ca, consistent with a reduced carrier mobility. Our results demonstrate that off-ladder impurities can affect both the low-energy magnetic excitations and superconducting correlations in the CuO₄ plaquettes. Finally, our study characterizes the magnetic and charge fluctuations in the phase from which superconductivity emerges in SCCO at elevated pressures.