LOW-TEMPERATURE PHASE-DIAGRAM OF YBBIPT

Resistivity measurements are reported on the cubic heavy-fermion compo und YbBiPt at ambient and hydrostatic pressures to approximate to 19 k bar and in magnetic fields to 1 T. The phase transition at T-c=0.4 K i s identified by a sharp rise in resistivity. That feature is used to b uild low-temperature H-T and P-T phase diagrams. The phase boundary in the H-T plane follows the weak-coupling BCS expression remarkably wel l from T-c to T-c/4, while small hydrostatic pressure of approximate t o 1 kbar suppresses the low-temperature phase entirely. These effects of hydrostatic pressure and magnetic field on the phase transition are consistent with an spin-density-wave (SDW) formation in a very heavy electron band at T=0.4 K. Outside of the SDW phase at low temperature, hydrostatic pressure increases the T-2 coefficient of resistivity, si gnaling an increase in heavy-fermion correlations with hydrostatic pre ssure. The residual resistivity decreases with pressure, contrary to t rends in other Yb heavy-fermion compounds.