Pseudogap studied by optical conductivity spectra of Zn-substituted YBa$_{2}$Cu$_{3}$O$_{y}$

The pseudogap and the superconducting gap cause a similar suppression of the low energy optical conductivity, but the behaviors of the spectral weight transfers are different, which enables us to distinguish these two gaps. In the \textit{c}-axis spectra of YBa$_{2}$Cu$_{3}$O$_{y}$, however, it is difficult to discuss these spectral weight transfers because of the additional structures due to a transverse Josephson plasma mode [1]. To overcome this problem, we substituted Zn for Cu, which is known to suppress those supplementary structures [2]. In this study, we performed temperature dependent reflectivity measurements in Zn-substituted YBa$_{2}$Cu$_{3}$O$_{y} $ system. We have revealed the continuous transfer of the low energy spectral weight to the higher energy region even below Tc, which suggests the coexistence of the pseudogap and the superconducting gap. [1]C. Bernhard et al. Phys. Rev. B, 61 (2000) 618. [2]R. Hauff et al., Phys. Rev. Lett., 77 (1996) 4620.