Evidence for strongly coupled charge-density-wave ordering in three-dimensional R5Ir4Si10 compounds from optical measurements

We report optical spectra of Lu5Ir4Si10 and Er5Ir4Si10, exhibiting the phenomenon of coexisting superconductivity or antiferromagnetism and charge-density wave (CDW) order. We measure the maximum value of the charge-density wave gap present on part of the Fermi surface of Lu5Ir4Si10, corresponding to a ratio 2 Delta/k(B)T(CDW)similar or equal to 10, well above the value in the limit of weak electron-phonon coupling. Strong electron-phonon coupling was confirmed by analyzing the optical conductivity with the Holstein model describing the electronphonon interactions, indicating the coupling to phonons centered at 30 meV, with a coupling constant lambda approximate to 2.6. Finally we provide evidence that approximately 16% of the Fermi surface of Lu5Ir4Si10 becomes gapped in the CDW state.