Optical spectroscopy study of charge density wave order in Sr_3 Rh_4 Sn_(13) and (Sr_(0.5) Ca_(0.5) )_3 Rh_4 Sn_(13)

We perform optical spectroscopy measurement on single-crystal samples of Sr_3 Rh_4 Sn_(13) and (Sr_(0 . 5) Ca_(0 . 5) )_3 Rh_4 Sn_(13) . 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 σ_1 ( ω ) below T CDW indicates that the Fermi surface is only partially gapped in the CDW state. The obtained value of 2 ?/ k_B T_(CDW) is roughly 13 for both Sr_3 Rh_4 Sn_(13) and (Sr_(0 . 5) Ca_(0 . 5) )_3 Rh_4 Sn_(13) 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.supported by the National Natural Science Foundation of China,the National Key Research and Development Program of China,the Ministry of Science and Technology of Taiwan中国科学引文数据库(CSCD)4047011-1-047011-66