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Jeudi 23 Octobre 2014, 14h
Amphi Holweck, Esc C, 1ème etage
Nematicity in iron-based superconductors
Yann Gallais
Matériaux et Phénomènes Quantiques (UMR CNRS 7162), Université Paris Diderot, Paris, France
Electronic analogues of nematic states, in which rotational symmetry is broken but translational invariance is preserved, have been proposed in a variety of correlated materials, such as quantum Hall systems, cuprates, ruthenates, heavy fermions , and, more recently, iron based superconductors [1]. In the iron-based superconductors several experiments have collected evidence that the tetragonal- to-orthorhombic structural transition is driven not by the lattice, but by electronic nematicity [2]. However it remains a challenge to disentangle the roles of the spin, charge, and orbital degrees of freedom in the nematic instability. In my talk I will discuss our recent electronic Raman scattering measurements which demonstrate the presence of charge nematic fluctuations in the tetragonal phase of both hole and electron doped systems [3]. In addition we observe an asymmetry in the behavior of nematic fluctuations between electron and hole doped BaFe2As2 which parallels the significantly reduced transport anisotropy found in the hole doped side. I will discuss the implications of our results for the mechanism of the nematic/orthorhombic transition in these systems.
[1] E. Fradkin et al. Ann. Rev. Cond Matter. Phys. 1, 197 (2010)
[2] R. M. Fernandes et al. Nature Phys. 10, 97 (2014)
[3] Y. Gallais et al., Phys. Rev. Lett., 111, 267001 (2013)
Work performed in collaboration with : P. Massat, L. Chauvière, Y.-X. Yang, R. M. Fernandes, I. Paul, M. A. Méasson, M. Cazayous, A. Sacuto, H.H. Wen, D. Colson, A. Forget, A. F. Wang and X. H. Chen.