Electron-hole symmetry in quasiparticle spectral weight of cuprates observed via infrared and photoemission spectroscopy

Abstract

We performed an optical spectroscopy study on single crystals of Pr 0.85 LaCe 0.15 CuO 4−δ (PLCCO) to revisit the electron-hole asymmetry, which has been understood as a fundamental property of cuprates. Four differently annealed samples -as-grown, reduced, optimally oxygenated, and over-oxygenated samples -were prepared, which have superconducting transition temperatures, T c = 0, 15, 24, and 18 K, respectively. We observed that low-energy quasiparticle spectral weights of all the PLCCO samples are significantly small in comparison with those of other electron-doped cuprate families. Instead, they are rather close to those of hole-doped counterpart La 2−x Sr x CuO 4 (LSCO). Accordingly, estimated effective carrier numbers per Cu atom (N eff /Cu) of superconducting samples are also considerably small, despite their relatively high critical temperatures. Complementary photoemission study reveals that the low-energy quasiparticle spectral weight of PLCCO is much smaller than that of Nd 1.85 Ce 0.15 CuO 4−δ (NCCO), consistent with the optical results. Our observations demonstrate that PLCCO provides the electron-hole symmetry in quasiparticle spectral weight, and highlight the importance of Cu3d-O2p hybridization to understand the low-energy spectral weight transfer in doped cuprates.