A universally strong renormalization of the thermodynamic effective mass by electron-electron interactions in the high-T_c cuprates

The strength of the pairing interactions and the degree of effective mass renormalization in a superconductor are inextricably linked. In the high transition temperature T_c superconducting cuprates, it is debated whether the thermodynamic effective mass is moderately renormalized as in a conventional Bardeen-Schrieffer-Cooper (BCS) superconductor, or more strongly renormalized as is the case in liquid ³He. While existing estimates of the effective mass renormalization in the cuprates are based largely on photoemission measurements, questions remain as to whether this represents the elementary excitations of the many body state. To obtain the thermodynamic effective mass that is most relevant to thermodynamic properties of the superconducting state, one must refer to measurements of physical quantities that are a thermodynamic function of state such the magnetic quantum oscillation amplitude and the specific heat. The discovery of magnetic quantum oscillations in as many a seven distinct cuprate families makes such a thermodynamic endeavor much more viable today than it was when high temperature superconductivity was first discovered. Here, using the orbitally-averaged Fermi velocity as a means for combining quantum oscillation and calorimetry data (both at low and high temperatures) with new hole doping-dependent and magnetic field orientation-dependent measurements of the single layer mercury cuprate Hg1201, we arrive at a clear answer to the question of the overall thermodynamic effective mass renormalization in the cuprates.