Emergence of Orbital Nematicity in the Tetragonal Phase of BaFe2(As1-xPx)(2)

We report on As-75-NMR measurements in single crystalline BaFe2(As0.96P0.04)(2) for magnetic fields parallel to the orthorhombic [110](o) and [100](o) directions above the structural transition temperature T-S similar or equal to 121 K. A large difference in the linewidth between the two field directions reveals in-plane anisotropy of the electric field gradient, even in the tetragonal phase. This provides microscopic evidence of population imbalance between As-4p(x) and 4p(y) orbitals, which reaches vertical bar n(x) - n(y)vertical bar/vertical bar n(x) + n(y)vertical bar similar to 15% at T -> T-S and is a natural consequence of the orbital ordering of Fe-3d(xz) and d(yz) electrons. Surprisingly, this orbital polarization is found to be already static near room temperature, suggesting that it arises from the pinning of anisotropic orbital fluctuations by disorder. The effect is found to be stronger below similar to 160 K, which coincides with the appearance of nematicity in previous torque and photoemission measurements. These results impose strong constraints on microscopic models of the nematic state.