Hall number inYbRh2Si2

Abstract

Recent experimental studies have revealed an abrupt change in the Hall number at a field tuned quantum critical point in the heavy fermion magnet ${\mathrm{YbRh}}_2{\mathrm{Si}}_2$. We investigate this by calculating the local density band structure for this metal and the appropriate transport integrals. We find the Fermi surface to be multisheeted with the two largest sheets having opposite sign contributions to the Hall number. Small changes in the $f$ electron occupation are sufficient to reproduce the observed large change in the Hall number. This suggests that ${\mathrm{YbRh}}_2{\mathrm{Si}}_2$ may be an example of a quantum critical valence fluctuator.