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

Abstract

We performed an optical spectroscopy study of single crystals of ${\mathrm{Pr}}_{0.85}{\mathrm{LaCe}}_{0.15}{\mathrm{CuO}}_{4\ensuremath{-}\ensuremath{\delta}}$ (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 overoxygenated samples---were prepared, which have superconducting transition temperatures ${T}_{c}=0$, 15, 24, and 18 K, respectively. We observed that the 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 their hole-doped counterpart ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$. Accordingly, estimated effective carrier numbers ${N}_{\mathrm{eff}}$ per Cu atom of superconducting samples are also very small, despite their relatively high critical temperatures. A complementary photoemission study reveals that the low-energy quasiparticle spectral weight of PLCCO is much smaller than that of ${\mathrm{Nd}}_{1.85}{\mathrm{Ce}}_{0.15}{\mathrm{CuO}}_{4\ensuremath{-}\ensuremath{\delta}}$, consistent with the optical results. Our observations demonstrate that PLCCO provides the electron-hole symmetry in the quasiparticle spectral weight and highlight the importance of Cu $3d$--O $2p$ hybridization to understand the low-energy spectral weight transfer in doped cuprates.