Infrared Spectroscopy Study Of The Topological Nodal-line Semimetals ZrSiS

Topological quantum materials have many classifications,including topological insulators,topological superconductors and topological semimetals.In these materials,the nodal-line semimetals is very special.By broking time reversal or spatial inversion symmetry,the nodal-line semimetals can be transformed into other semimetals such as Dirac semimetals and Wely semimetals.It is considered as the parent materials of other semimetals,so the study of topological nodal-line semimetals is especially important.Infrared spectroscopy is an experimental technique that accurately measures charge excitation in materials and provides us with a wealth information of charge dynamics and energy band structure.Infrared photons are to excite the electrons in the occupied state to the unoccupied state.The optical response of the free electrons can be clearly obtained.At the same time,the transition behavior of electrons in the bulk state of the material can be detected,and the corresponding band structure and energy gap characteristics can be obtained.In this thesis,ZrSiS single crystals were growed by the chemical vapor transport（CVT）.The DC transport measurement proved that this material is a good metal with extremely low resistivity.ZrSiS has the lowest resistivity of any sulfide known.We used infrared spectroscopy to study the optical properties of topological nodal-line semimetals ZrSiS.The reflectivity of ZrSiS near the zero frequency is almost equal to 1.0 at each temperature,indicating that ZrSiS has metallic properties.It is temperature dependence over a wide frequency range of 60 cm^-1 to25000 cm^-1.We proved that ZrSiS has a quasi-two-dimensional flat optical conductivity similar to graphene,also pointed out that corresponding band transitions in the energy band structure of 12000 cm^-1,14200 cm^-1 and 16900 cm^-1 vicinity in the high frequency region.