Non-universal pairing symmetry and pseudogap phenomena in hole- and electron-doped cuprate superconductors

Experimental studies of the pairing state of cuprate superconductors reveal asymmetric behaviors of the hole-doped (p-type) and electron-doped (n-type) cuprates. The pairing symmetry, pseudogap phenomenon, low-energy spin excitations and the spatial homogeneity of the superconducting order parameter appear to be non-universal among the cuprates, which may be attributed to competing orders. We propose that the non-universal pseudogap and nano-scale variations in the quasiparticle spectra may be the result of a charge nematic (CN) phase stabilized by disorder in highly two-dimensional (2D) p-type cuprates. The CN phase is accompanied by gapped spin excitations and competes with superconductivity (SC). In contrast, gapless spin excitations may be responsible for the absence of pseudogap and the presence of excess sub-gap spectral weight in the momentum-independent quasiparticle spectra of n-type cuprates. The physical implications and further verifications for these conjectures are discussed.