Field-induced Fermi surface reconstruction and adiabatic continuity between antiferromagnetism and hidden-order state in URu$_2$Si$_2$

Shubnikov-de Haas oscillations at very low temperatures and high magnetic fields reveal an abrupt reconstruction of the Fermi surface within the hidden-order phase of URu$_{2}$Si$_{2}$. Taken together with reported Hall effect results, this implies an increase in the effective carrier density and suggests spectrum of itinerant quasiparticles. While hydrostatic pressure favors antiferromagnetism in detriment to the hidden-order state, we found that it has a modest effect on the complex $H-T$ phase diagram. This suggests adiabatic continuity between the hidden-order and antiferromagnetism.