title: Origin of the tetragonal-to-orthorhombic phase transition in FeSe: a combined thermodynamic and NMR study of nematicity.
abstract: The nature of the tetragonal-to-orthorhombic structural transition at T_{s}≈90  K in single crystalline FeSe is studied using shear-modulus, heat-capacity, magnetization, and nuclear magnetic resonance measurements. The transition is shown to be accompanied by a large shear-modulus softening, which is practically identical to that of underdoped Ba(Fe,Co)_{2}As_{2}, suggesting a very similar strength of the electron-lattice coupling. On the other hand, a spin-fluctuation contribution to the spin-lattice relaxation rate is only observed below T_{s}. This indicates that the structural, or "nematic," phase transition in FeSe is not driven by magnetic fluctuations.
authors: Institut für Festkörperphysik, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany.
authors: A E
authors: AE
authors: Böhmer
authors: Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors: T
authors: T
authors: Arai
authors: Institut für Festkörperphysik, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany.
authors: F
authors: F
authors: Hardy
authors: Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors: T
authors: T
authors: Hattori
authors: Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors: T
authors: T
authors: Iye
authors: Institut für Festkörperphysik, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany.
authors: T
authors: T
authors: Wolf
authors: Institut für Festkörperphysik, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany.
authors: H V
authors: HV
authors: Löhneysen
authors: Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors: K
authors: K
authors: Ishida
authors: Institut für Festkörperphysik, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany.
authors: C
authors: C
authors: Meingast