Specific heat in a mean-field-like solid: KDP above the critical electric field

Measurements of the specific heat in KDP (KH 2 PO 4 ) at ambient pressure and electric fields above the critical field E c are presented and analysed. The specific heat at E>E c shows a remarkably strong anomaly which is shifted upwards in temperature and reduced in sharpness with increasing electric field. The results can be satisfactorily accounted for by Landau theory provided terms are included in the free-energy expansion to describe the strong saturation behaviour at large polarisation. This use of mean-field theory is fully consistent with theoretical analysis which has shown that KDP has an upper critical dimensionality below three.