UC Davis

Nuclear magnetic resonance studies of 75As under uniaxial stress were conducted on theparent and Co-doped BaFe2As2 iron-based superconductors. An NMR strain probe, that incorporates piezoelectric-based apparatus from Razorbill Instruments, was designed to apply the uniaxial stress. Nuclear quadrupolar splittings of the parent compound were measured as a function of strain. The electric eld gradient tensor responds linearly to the presence of a strain eld in the paramagnetic phase. The nematic susceptibility was extracted from the slope of this linear response as a function of temperature and it diverges near the structural transition. The detailed spin-lattice relaxation rate dependence on strain was measured for the parent BaFe2As2. The magnetic uctuation spectrum in the paramagnetic phase acquires an anisotropic response in spin-space upon application of a tetragonal symmetry-breaking strain eld. This result unveils an internal spin structure of the nematic order parameter, indicating that electronic nematic materials may oer a route to magneto-mechanical control. A second horseshoe device was used to apply strain, and the in-plane anisotropy of spin-lattice relaxation rate under uniaxial stress was measured in Co-doped BaFe2As2. The anisotropy reaches a maximum of 30% at TN, and the recovery data reveal that the glassy behavior of the spin uctuations present in the twinned state persist in the fully detwinned crystal. xi