Search for orbital moments in underdoped cuprate metals

Abstract

Polarized neutron-diffraction experiments have been performed in search of the orbital magnetic moments recently predicted in a theory for the cuprate metals. Both ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4} [\mathrm{LSCO}(x)]$ and ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+x} [\mathrm{YBCO}(x)]$ compounds were investigated. No definitive evidence for the existence of such a three-dimensionally ordered moment was found in any of these samples within experimental uncertainty, which was as low as $0.01{\ensuremath{\mu}}_{B}.$ We have also investigated the possibility that a magnetic rod exists parallel to the c axis in the case of two- or quasi-two-dimensional ordering in the $(a,b)$ plane and have set an upper limit for the total moment to be $0.1{\ensuremath{\mu}}_{B}$ in LSCO $(x=0.1).$