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 correspo nding to high-temperature superconductors (HTS's). In the case of s wa ve pairing (in the absence of the magnetic order) it is found that whe n the exchange energy h(ex) is larger than the SC order parameter Delt a, 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 gi ves rise to power-law behavior with respect to temperature and frequen cy of various quantities. The Knight shift, the electronic Raman scatt ering, the ultrasound attenuation and the specific heat are calculated . The phase change of the pairing amplitude on the Fermi surface and i ts possible consequence for the Josephson effect is discussed briefly. This theory might also be applicable to the heavy-fermion systems lik e U Pt-3, U Be-13, U Ru2Si2, U Pd2Al3, U Ni2Al3, and to the rare-earth borocarbides HoNi2B2C.