Observation of Orbital Currents in CuO

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Science  07 Apr 2011:
DOI: 10.1126/science.1201061


Orbital currents are proposed to be the order parameter of the pseudo-gap phase of cuprate high-Tc superconductors. We use resonant x-ray diffraction to observe orbital currents in a copper-oxygen plaquette, the basic building block of cuprate superconductors. The confirmation of the existence of orbital currents is an important step towards the understanding of the cuprates as well as materials lacking inversion symmetry, such as magnetically induced multiferroics. While observed in the antiferromagnetic state of cupric oxide, it is shown that orbital currents can occur even in the absence of long-range magnetic moment ordering.