Evolution of Quasiparticle Properties inUGe2with Hydrostatic Pressure Studied via the de Haas–van Alphen Effect

We report measurements of the de Haas–van Alphen effect in $\mathrm{UGe}{}_2$ under hydrostatic pressures up to 17.6 kbar, exceeding the critical pressure $P_c$ for the suppression of ferromagnetism. A discontinuous change of the Fermi surface is found to occur across $P_c$. Substantially enhanced effective masses $\left(\sim {40m}_e\right)$ are found near $P_c$ on both the ferromagnetic and the paramagnetic sides.