Magnetic Torque Evidence for Broken Rotational Symmetry in the Tetragonal Phase of BaFe$_{2}$(As$_{1-x}$P$_{x})_{2}$ Single Crystals

The emergence of broken four-fold symmetry is found in the tetragonal phase of BaFe$_{2}$(As$_{1-x}$P$_{x})_{2}$ single crystals [1] by in-plane anisotropy measurements of magnetic susceptibility. Magnetic torque detects a spontaneous growth of two-fold oscillations under in-plane field rotations, whose amplitude is linked to an order parameter of an electronic ``nematic'' phase. Our findings reveal that the spontaneous rotational symmetry breaking sets in far above the tetragonal to orthorhombic structural transition, which might be also linked to the unconventional superconductivity of this system [2,3]. \\[4pt] [1] S. Kasahara, et al., Phys. Rev. B 81, 184519 (2010). \\[0pt] [2] K. Hashimoto, et al., Phys. Rev. B 81, 220501(R) (2010). \\[0pt] [3] Y. Nakai, et al., Phys. Rev. B 81, 020503(R) (2010).