Optical observation of intercalation-induced symmetry breaking in Fe$_{\mathrm{x}}$-TaS$_{\mathrm{2}}$

Fe$_{\mathrm{\thinspace }}$intercalated TaS$_{\mathrm{2}}$ single crystals exhibit interesting domain patterns at room temperature with the concentration of 1/4 and 1/3. In this work, we measured the optical spectrum and Raman response of Fe$_{\mathrm{1/4}}$TaS$_{\mathrm{2\thinspace }}$and Fe$_{\mathrm{1/3}}$TaS$_{\mathrm{2}}$, and compared this data with the parent compound 2H-TaS$_{\mathrm{2.\thinspace }}$The optical conductivity data indicates a strong free carrier response, and Fe intercalation induced both $d-d$ excitations and new phonon modes compared to the parent compound that are strongly related to the symmetry breaking of the parent compound. Our findings were in good agreement with first principle calculations.