How Do Heavy Fermions Get Polarized And Die?
In paramagnetic heavy fermion systems the f-spins dissolve into Kondo singlets and reappear within the Fermi volume, producing a “large” Fermi surface populated by heavy quasiparticles. According to theory, when a very large magnetic field is applied to such a system the Kondo singlets are broken and the fully polarized bare f-spins vanish from the Fermi volume, leaving behind a “small” Fermi surface populated by light quasiparticles. How the system passes from the low-field to the high-field limit is not clear. This talk will discuss recent transport and de Haas van Alphen studies of the archetypal heavy fermion systems $\rm CeRu_2Si_2$ [1] and $\rm YbRh_2Si_2$ [2], which are interpreted as showing that the f-electron disappears from the Fermi volume via two successive Lifshitz transitions: in the first transition a majority spin band sinks below the Fermi level, while in the second a new minority spin band appears at the Fermi level. While this interpretation is in accord with rece
