Observation of a 500meV Collective Mode in La2-xSrxCuO4 and Nd2CuO4
Abstract
Utilizing resonant inelastic x-ray scattering, we report a previously unobserved mode in the excitation spectrum of La2-xSrxCuO4 at 500 meV. The mode is peaked around the (π,0) point in reciprocal space and is observed to soften, and broaden, away from this point. Samples with x=0, 0.01, 0.05, and 0.17 were studied. The new mode is found to be rapidly suppressed with increasing Sr content and is absent at x=0.17, where it is replaced by a continuum of excitations. The peak is only observed when the incident x-ray polarization is normal to the CuO planes and is also present in Nd2CuO4. We suggest possible explanations for this excitation.
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