THEORY OF ELECTRON-HOLE ASYMMETRY IN DOPED CUO2 PLANES

The magnetic phase diagrams, and other physical characteristics, of th e hole-doped La2-xSrxCuO4 and electron-doped Nd2-xCexCuO4 high-tempera ture superconductors are profoundly different. Given that it is envisa ged that the simplest Hamiltonians describing these systems are the sa me, viz., the t-t'-J model, this is surprising. Here we relate these p hysical differences to their ground states' single-hole quasiparticles , the spin distortions they produce, and the spatial distribution of c arriers for the multiply doped systems. As is well known, the low dopi ng limit of the hole-doped material corresponds to k = (pi/2, pi/2) qu asiparticles, states that generate so-called Shraiman-Siggia long-rang ed dipolar spin distortions via backflow. These quasiparticles have be en proposed to lead to an incommensurate spiral phase, an unusual scal ing of the magnetic susceptibility, as well as the scaling of the corr elation length defined by xi(-1)(x, T) = xi(-1)(x, 0) + xi(-1)(0, T), all consistent with experiment. We suggest that for the electron-doped materials the single-hole ground state corresponds to k = (pi, 0) qua siparticles; we show that the spin distortions generated by such carri ers are shortranged. Then, we demonstrate the effect of this single-ca rrier difference in many-carrier ground states via exact diagonalizati on results by evaluating S(q) for up to four carriers in small cluster s. Consistent with experiment, for the hole-doped materials short-rang ed incommensurate spin orderings are induced, whereas for the electron -doped system only commensurate spin correlations are found. Further, we propose that there is an important difference between the spatial d istributions of mobile carriers for these two systems: for the hole-do ped material the quasiparticles tend to stay far apart from one anothe r, whereas for the electron-doped material we find tendencies consiste nt with the clustering of carriers, and possibly of low-energy fluctua tions into an electronic phase-separated state. Phase separation in th is material is consistent with the midgap states found by recent angle -resolved photoemission spectroscopy studies. Last, we propose the ext rapolation of an approach based on the t-t'-J model to the hole-doped 123 system.