Thermoelectric Coefficients of the Quantum Critical β-YbAlB4

Abstract

We report the low-temperature thermoelectric power S ( T ) on high-quality single crystals of β-YbAlB 4 down to 40 mK. β-YbAlB 4 is the first Yb-based heavy fermion superconductor with the transition temperature of T c ∼ 80 mK, and stoichiometrically quantum critical at ambient pressure and under zero magnetic field. In the vicinity of a quantum critical point, S ( T )/ T exhibits a dramatic enhancement and takes large negative values at low temperatures. By contrast, when the system goes into the Fermi liquid state by applying the magnetic field, S ( T )/ T becomes constant. From the comparative study using the different quality samples, we confirm that the thermoelectric power is a good probe to elucidate the low-energy electronic excitations of the strongly correlated metals. The apparently different behaviors of the dimensionless ratio q of the thermoelectric power S and the specific heat C between β-YbAlB 4 and YbRh 2 Si 2 toward the QCP suggest that the systems belong to distinct classes of the quantum criticality.