Does the Fermi volume of YbRh2Si2 jump at its critical field

In YbRh2Si2 at $T \to 0$ across the critical field $B_c \sim 600\,\mathrm{G}$ (field in the ab plane), determine whether the Fermi volume changes discontinuously from large (including the 4f hole) to small, as inferred from the Hall crossover whose width scales with $T$. An answer is a $T = 0$ extrapolation of the crossover width of Fermi-volume-sensitive transport (Hall coefficient, thermopower) in crystals with residual resistivity ratio of order 100 or more, or a Fermi-surface measurement at fields close to $B_c$, for example on chemically substituted samples whose critical field lies in the range accessible to quantum oscillations.

Hall and thermopower crossover widths measured below 10 mK on the cleanest crystals and extrapolated to $T = 0$, together with Fermi-surface data on substituted samples whose critical field is high enough for quantum oscillations.