Uncovering a pressure-tuned electronic transition in BiSrYCu2O8 using   Raman scattering and x-ray diffraction
  We report pressure tuned Raman and x-ray diffraction data of Bi1.98Sr2.06Y0.68Cu2O8 revealing a critical pressure at 21 GPa with anomalies in six physical quantities: electronic Raman background, electron-phonon coupling, spectral weight transfer from high to low frequency, density dependent behaviour of phonon and magnon frequencies, and a compressibility change in the c-axis. For the first time in a cuprate, mobile charge carriers, lattice, and magnetism all show anomalies at a distinct critical pressure in the same experimental setting. Furthermore, the Raman spectral changes are similar to that seen traversing the superconducting dome with doping, suggesting that the critical pressure at 21 GPa is related to the much discussed critical point at optimal doping. 
T. Cuk, V. Struzhkin, T.P. Devereaux, A. Goncharov, C. Kendziora, H.   Eisaki, H. Mao, and Z.-X. Shen