1206.2938 (S. Arsenijević et al.)

Spin fluctuation driven enhancement of thermopower near the quantum
critical point in Ba(Fe(1-x)Co(x))2As2    [PDF]

S. Arsenijević, H. Hodovanets, R. Gaál, L. Forró, S. L. Bud'ko, P. C. Canfield

We demonstrate that the thermopower (S) can be used to probe the spin fluctuations (SF) in the proximity to the quantum critical point (QCP) in Fe-based superconductors. The sensitivity of S to the entropy of charge carriers allows us to observe an increase of S/T in Ba(Fe(1-x)Co(x))2As2 close to the spin-density-wave (SDW) QCP. This behavior is due to the coupling of low-energy conduction electrons to two-dimensional SF, similar to the heavy-fermion systems. The low-temperature enhancement of S/T in the doping range 0.02 < x < 0.1 is bordered by the two Lifshitz transitions, and it corresponds to the superconducting doping region, where similarity between the electron and nonreconstructed hole pockets exists. The maximal S/T is observed in the proximity of commensurate-to-incommensurate SDW transition, for critical x_c ~ 0.06, close to the highest superconducting T_c. This analysis indicates that the low-T thermopower is influenced by the critical spin fluctuations which are important for the superconducting mechanism.

View original: http://arxiv.org/abs/1206.2938