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${}_{4-\delta }$ (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 ($N_{\mathrm{eff}}$/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${}_{4-\delta }$ (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 Cu3$d$-O2$p$ hybridization to understand the low-energy spectral weight transfer in doped cuprates.

17 pages, 4 figures