Spin-waves in the mid-infrared spectrum of antiferromagnetic YBa ₂ Cu ₃ O _6.0

Abstract

The mid-infrared spin-wave spectrum of antiferromagnetic\nYBa$_2$Cu$_3$O$_{6.0}$\\ was determined by infrared transmission and reflection\nmeasurements ($\\bbox{k} \\!\\! \\parallel $c) at $T\\!=\\!10\\!$~K.\\@ Excitation of\nsingle magnons of the optical branch was observed at\n$E_{\\text{op}}\\!=\\!178.0\\!$~meV.\\@ Two further peaks at $346\\!$~meV\n($\\approx\\!1.94\\,E_{\\text{op}}$) and $470\\!$~meV\n($\\approx\\!2.6\\,E_{\\text{op}}$) both belong to the two-magnon spectrum. Linear\nspin wave theory is in good agreement with the measured two-magnon spectrum,\nand allows to determine the exchange constant $J$ to be about $120\\!$~meV,\nwhereas the intrabilayer coupling $J_{12}$ is approximately $0.55\\,J$.\n