FIELD-DEPENDENCE OF THE SPECIFIC-HEAT OF SINGLE-CRYSTAL HGBA2CA2CU3O8+DELTA

Using a sensitive sc technique, we have measured the specific heat (C) of a small single crystal of HgBa2Ca2Cu3O8+delta in fields up to 7 T. In zero field the superconducting anomaly has the form of a quasiloga rithmic peak, which is almost symmetric about T-c. In increasing field s the anomaly is strongly suppressed and is shifted to lower temperatu res (with a slope of similar to -0.8 K/T). This unusual behavior is qu alitatively different from that of YBa2Cu3O6.95, and seems to be intri nsic to the quasi-two-dimensional, high-T-c superconductors. We find t hat the three-dimensional XY model of critical fluctuations best descr ibes our data.