Optical spectroscopy study of charge density wave order in Sr3Rh4Sn13 and (Sr0.5Ca0.5)(3)Rh4Sn13

We perform optical spectroscopy measurement on single-crystal samples of Sr3Rh4Sn13 and (Sr0.5Ca0.5)(3)Rh4Sn13. Formation of CDW energy gap was clearly observed for both single-crystal samples when they undergo the phase transitions. The existence of residual Drude components in sigma(1)(omega) below T-CDW indicates that the Fermi surface is only partially gapped in the CDW state. The obtained value of 2 Delta/k(B)T(CDW) is roughly 13 for both Sr3Rh4Sn13 and (Sr0.5Ca0.5)(3)Rh4Sn13 compounds, which is considerably larger than the mean-field value based on the weak-coupling BCS theory. The measurements provide optical evidence for the strong coupling characteristics of the CDW phase transition.National Natural Science Foundation of China [11327806, GZ1123]; National Key Research and Development Program of China [2016YFA0300902]; Ministry of Science and Technology of Taiwan [MOST-103-2112-M-006-014-MY3]SCI(E)ARTICLE46