1207.3852 (A. F. Wang et al.)

Electronic Nematicity in Pseudogap-like Phase diagram of
NaFe$_{1-x}$Co$_x$As    [PDF]

A. F. Wang, J. J. Ying, X. G. Luo, Y. J. Yan, D. Y. Liu, Z. J. Xiang, P. Cheng, G. J. Ye, L. J. Zou, Z. Sun, X. H. Chen

Electronic nematicity, which breaks the C$_4$ rotational symmetry of underlying lattice, has been observed by various techniques in underdoped ferropnictides, accompanying the structural transition from tetragonal to orthorhombic. Recent magnetic torque measurements suggest that the electronic nematicity develops above the structural and superconducting transitions. However, there lacks evidence directly related to electronic excitations for the nematic transition. Symmetry breaking in electronic states can change low-lying electronic excitations and manifest itself in transport properties. Here we report electronic transport measurements on single crystals of NaFe$_{1-x}$Co$_x$As system. We found that the cotangent of Hall angle, cot$\theta_{\rm H}$, follows $T^3$-dependence in all the superconducting samples. A deviation develops below a characteristic temperature $T^*$ well above the structural and superconducting transitions, accompanied by a departure from power-law temperature dependence and the emergence of in-plane anisotropy in resistivity. These properties signify the emergence of electronic nematicity, which is found to exist in the whole superconducting regime. The doping dependence of $T^*$ resembles the crossover line of pseudogap phase in cuprates. Our finding suggests that the electronic nematicity plays an important role for superconductivity.

View original: http://arxiv.org/abs/1207.3852