Drastic change of the Fermi surface across the metamagnetic transition in CeRh₂Si₂

We report high field de Haas-van Alphen (dHvA) effect measurements in CeRh$_2$Si$_2$ both below and above the first-order 26 T metamagnetic transition from an antiferromagnetic to a polarized paramagnetic state. The dHvA frequencies observed above the transition are much higher than those observed below, implying a drastic change of the Fermi-surface size. The dHvA frequencies above the transition and their angular dependence are in good agreement with band-structure calculations for LaRh$_2$Si$_2$, which correspond to CeRh$_2$Si$_2$ with localized $f$ electrons. Given that the $f$ electrons are also localized at low fields in CeRh$_2$Si$_2$, the Fermi-surface reconstruction is due to the suppression of antiferromagnetism and the restoration of the crystallographic Brillouin zone rather than the delocalization of the $f$ electrons. This example suggests that the intuitive notation of "small" and "large" Fermi surfaces commonly used for localized and itinerant $f$ electrons, respectively, requires careful consideration, taking into account the modification of the Brillouin zone in the antiferromagnetic state, when interpreting experimental results.