Thermopower investigations of YbRh2Si2 in the vicinity of an antiferromagnetic quantum critical point

The stoichiometric heavy-fermion compound YbRh2Si2 exhibits an antiferromagnetic (AFM) phase transition at an extremely low temperature of TN = 72 mK. Upon applying a tiny magnetic field the AFM ordering is suppressed and the system is driven towards a quantum critical point (QCP). Furthermore, an additional energy scale at T* indicating the crossover from local to itinerant character of the 4f electron vanishes at the QCP. Here, we report on measurements of the thermoelectric power S of high quality single crystals from 6 K down to 50 mK in fields up to 2 T. S(T) was measured within the easy ab plane of the system, that exhibits a critical field of only 50 mT. In the critical region S/T diverges upon approaching the QCP, while it exhibits a constant value in the Fermi liquid regime at higher fields. The low temperature behavior of the thermopower in YbRh2Si2 is discussed in detail and compared to available theoretical predictions. Whether the T* line observed in Hall effect and magnetostriction measurements can also be resolved in the thermopower is a matter of great interest