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Charge-Transfer Excitations in the Model Superconductor HgBa$_2$CuO$_{\bf 4+δ}$

L. Lu·X. Zhao·G. Chabot-Couture·J. N. Hancock·N. Kaneko·O. P. Vajk·G. Yu·S. Grenier·Y. J. Kim·D. Casa·T. Gog·M. Greven
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Abstract

We report a Cu $K$-edge resonant inelastic x-ray scattering (RIXS) study of charge-transfer excitations in the 2-8 eV range in the structurally simple compound HgBa$_2$CuO$_{4+δ}$ at optimal doping ($T_{\rm c} = 96.5 $ K). The spectra exhibit a significant dependence on the incident photon energy which we carefully utilize to resolve a multiplet of weakly-dispersive ($ < 0.5$ eV) electron-hole excitations, including a mode at 2 eV. The observation of this 2 eV excitation suggests the existence of a charge-transfer pseudogap deep in the superconducting phase. Quite generally, our data demonstrate the importance of exploring the incident photon energy dependence of the RIXS cross section.

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L. Lu, X. Zhao, G. Chabot-Couture, J. N. Hancock, N. Kaneko, O. P. Vajk, G. Yu, S. Grenier, Y. J. Kim, D. Casa, T. Gog, M. Greven. 2005-09-08. Charge-Transfer Excitations in the Model Superconductor HgBa$_2$CuO$_{\bf 4+δ}$. https://doi.org/10.1103/physrevlett.95.217003

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