Unconventional charge-density wave in Sr3Ir4Sn13 cubic superconductor revealed by optical spectroscopy study

Sr₃Ir₄Sn₁₃ is an interesting compound showing the coexistence of structural phase transition and superconductivity. The structural phase transition at 147 K leads to the formation of a superlattice. We perform optical spectroscopy measurements across the structural phase transition on single-crystal samples of Sr₃Ir₄Sn₁₃. The optical spectroscopy study reveals an unusual temperature-induced spectral weight transfer over a broad energy scale, yielding evidence for the presence of electron correlation effects. Below the structural phase transition temperature an energy gap-like suppression in optical conductivity was observed, leading to the removal of partial itinerant carriers near the Fermi level. Unexpectedly, the suppression appears at a much higher energy scale than expected for the usual charge-density-wave phase transition.