EXTENDED S-WAVE AND GAPLESS SUPERCONDUCTIVITY DUE TO ANTIFERROMAGNETISM A MODEL INSPIRED BY HTS

We present a model of a superconductor (SC) in the presence of spiral or antiferromagnetic (AF) order with a quasiparticle spectrum corresponding to high-temperature superconductors (HTS's). In the case of s wave pairing (in the absence of the magnetic order) it is found that when the exchange energy h(ex) is larger than the SC order parameter Delta, i.e. h(ex)greater than or equal to Delta, the superconductivity is of the extended s wave type and the quasiparticle spectrum is gapless with nodes on either side of the (pi, pi) diagonal in k space, This gives rise to power-law behavior with respect to temperature and frequency of various quantities. The Knight shift, the electronic Raman scattering, the ultrasound attenuation and the specific heat are calculated. The phase change of the pairing amplitude on the Fermi surface and its possible consequence for the Josephson effect is discussed briefly. This theory might also be applicable to the heavy-fermion systems like U Pt-3, U Be-13, U Ru2Si2, U Pd2Al3, U Ni2Al3, and to the rare-earth borocarbides HoNi2B2C.