Abstract

The heavy fermion compound YbRh2Si2 has a rich temperature – magnetic field phase diagram, including an antiferromagnetic field-induced quantum critical point. The nature of the YbRh2Si2 Fermi surface, particularly its inclusion or exclusion of the Yb 4f quasihole degrees of freedom in various regions of the phase diagram, is of central importance to understanding the physics of this material.

In order to directly determine the field dependence of the YbRh2Si2 Fermi surface, we have performed de Haas-van Alphen effect measurements in the magnetic field range 8 T <= H <= 16 T [1, 2]. Our data reveal a continuous change of the extremal Fermi surface areas through H0 ~ 10 T, supporting the theory of a Lifshitz transition at H0. In such a scenario, a low-field “large” Fermi surface, including the 4f degrees of freedom, is increasingly spin split until a majority-spin branch disappears [3]. Combined with Luttinger’s theorem, our measurements are inconsistent with the proposal of 4f localization in this field range, in which the 4f degrees of freedom drop out of the Fermi surface at H0.

[1] P.M.C. Rourke et al., Phys. Rev. Lett. 101, 237205 (2008). [2] P.M.C. Rourke et al., J. Phys.: Conf. Ser. 150, 042165 (2009). [3] S. Viola Kusminskiy et al., Phys. Rev. B 77 , 094419 (2008).