We report results of resistivity measurements at ambient and hydrostatic pressures of up to ≈ 6 kbar. Large resistivity anisotropy sets in below the phase-transition temperature of 0.4 K. In some directions the resistivity increases below 0.4 K, which we interpret as partial gapping of the Fermi surface. Hydrostatic pressure of less than 1 kbar suppresses the low-temperature phase entirely. © 1994.

The compound YbBiPt exhibits an extremely large low-temperature C/T (γ∼8 J K-2 mol-1/Yb) which, if due solely to a renormalized effective mass, would make this material the heaviest correlated electron system known to date. In the Kondo model, the very large γ corresponds to a small characteristic energy scale that is expected to be pressure dependent. We have studied the effect of chemical pressure on YbBiPt single crystals by heat-capacity measurements on Y and Lu-doped samples. We have also made preliminary low-temperature measurements under hydrostatic pressure of the heat capacity (300 mK≤T≤2 K, up to 8 kbar) and resistance (30 mK≤T≤1 K, at 16 kbar).