발표자: 서유성

시간: 4월 11일 낮 12시

장소: 31317호

제목: Superfluid plasma frequency and condensation gap evolution in excitonic insulator, Ta2NiSe5

초록:

Ta₂NiSe₅ is an interesting anisotropic material, well known as one of the few excitonic insulators proposed over 50 years ago. Ta₂NiSe₅ has quasi-one dimensional chains along the a-axis. In this study, we have investigated the anisotropic optical properties of a single crystal Ta₂NiSe₅ along the a- and c-axes. The measured a- and c-axis optical conductivities exhibit large anisotropic electronic and phononic properties. With regard to the a-axis optical conductivity, a sharp peak near 3050 cm^-1 at 9 K, with a well-defined optical gap (∆^EI  ~1800 cm^-1) and a strong temperature dependence, is observed. With an increase in temperature, this peak broadens and the optical energy gap closes around ~ 325 K (Tc). The spectral weight redistribution with respect to the frequency and temperature indicates that the normalized optical energy gap (∆^EI(T)/ ∆^EI(0)) is 1- (T/Tc )². For the first time, the temperature-dependent superfluid plasma frequency of the excitonic condensation in Ta₂NiSe₅ (ω_sf  ~ 7180 cm^-1 at 9 K) has been determined from measured optical data. Our findings may pave the way for exciting new avenues for future research on excitonic insulators.