The possibility of phonon induced antiferromagnetic magnons in cuprate superconductors at low temperatures

Abstract

The strongly correlated electronic structures of cuprate high- T c superconductors are between that of the antiferromagnetic insulting parent and highly doped paramagnetic metals. And high T c is attainable only for a narrow range of oxidation states. This may be an indication that the electronic states of these superconductors are in the vicinity of the threshold for the creation of antiferromagnetic magnetic moments. Since the superexchange integrals are functions of the CuCu separations, lattice vibrations of the Cu atoms possibly induce local antiferromagmetic magnetic moments and magnons. A modified magnon (spin wave) formalism, based on small disturbances of antiferromagnetic magnetic moments in a non-magnetic system, has been done for these superconductors. The bare magnon spectrum is found to disperse linearly for small wave vectors like the conventional antiferromagnetic magnons. Phonon-magnon interactions are found to reduce short-wave-length magnon excitation energies so that these magnons may exist even at low temperatures.