Joint features of pressure effect and specific heat of RBa2Cu3Ox at distinct n(h) values

Investigations of specific heat and T-c under pressure are presented for YB a2Cu3Ox (Y123), NdBa2Cu3Ox (Nd 123) and Y1-yCayBa2Cu3Ox (YCa123) for variou s oxygen contents. In Y123, at the maximum of the specific-heat jump DeltaC /T-c the pressure dependence of the transition temperature dT(c)/dp shows a zero crossing. Inversely, at the maximum of dT(c)/dp the jump in the speci fic heat becomes minimal. With Ca doping these joint features shift to lowe r oxygen contents x, whereas Nd123 causes a shift into the opposite directi on. Considering the hole doping by Ca and the larger chain fragmentation in Nd123, we rescaled our results with respect to the hole content ni, in the CuO2 planes. In this plot the joint features coalesce in two fixed hole co ncentrations, n(h)approximate to0.11 and n(h)approximate to0.17, irrespecti ve of the substitution and doping. The maximum in DeltaC/T-c may be related to the appearance of a quantum critical point due to the disappearance of a pseudogap for hole contents above n(h)approximate to0.17. The features at n(h)approximate to0.11 point to a drastic change in system properties at t his hole content that may be connected to various anomalies found in other properties reported in the literature.