[Physics Journal Club] -2017.04.11
시간: 4월 11일 낮 12시
제목: Superfluid plasma frequency and condensation gap evolution in excitonic insulator, Ta2NiSe5
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 (ωsf ~ 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.