Optical Sum Rule Anomalies in the High-T c Cuprates

We provide a brief summary of the observed sum rule anomalies in the high-T _c cuprate materials. A recent issue has been the impact of a non-infinite frequency cutoff in the experiment. In the normal state, the observed anomalously high temperature dependence can be explained as a ‘cutoff effect’. The anomalous rise in the optical spectral weight below the superconducting transition, however, remains as a solid experimental observation, even with the use of a cutoff frequency.