For website front pageAuthors: S.-F. Wu, W.-L. Zhang, D. Hu, H.-H. Kung, A. Lee, H.-C. Mao, P.-C. Dai, H. Ding, P. Richard and G. Blumberg

Abstract:

We use electronic Raman scattering to study the low-energy excitations in BaFe2(As0.5P0.5)2 (Tc≈16 K) samples. In addition to a superconducting pair breaking peak (2Δ=6.7 meV) in the A1g channel with a linear tail towards zero energy, suggesting a nodal gap structure, we detect spectral features associated to Pomeranchuk oscillations in the A1g, B1g and B2g channels. We argue that the small Fermi energy of the system is an essential condition for these Pomeranchuk oscillations to be underdamped. The Pomeranchuk oscillations have the same frequencies in the B1g and B2g channels, which we explain by the mixing of these symmetries resulting from the removal of the σv and σd symmetry planes due to a large As/P disorder. Interestingly, we show that the temperature at which the peaks corresponding to the Pomeranchuk oscillations get underdamped is consistent with the non-Fermi liquid to Fermi liquid crossover determined by transport, suggesting that the Pomeranchuk instability plays an important role in the low-energy physics of the Fe-based superconductors.

 

fig1aAuthors: W.-L. Zhang, Athena S. Sefat, H. Ding, P. Richard, and G. Blumberg

Abstract:

We use polarized Raman scattering to study the structural phase transition in EuFe2As2, the parent compound of the 122-ferropnictide superconductors. The in-plane lattice anisotropy is characterized by measurements of the side surface with different strains induced by different preparation methods. We show that while a fine surface polishing leaves the samples free of residual internal strain, in which case the onset of the C4 symmetry breaking is observed at the nominal structural phase transition temperature TS, cutting the side surface induce a permanent fourfold rotational symmetry breaking spanning tens of degrees above TS.