Nematic Glassy Behavior Probed by NMR under Strain in Iron Pnictide Superconductors

NMR studies of Ba(M_xFe_1-x)2As2 (M = Co, Cu) have uncovered
inhomogeneous glassy dynamics via stretched exponential relaxation and
wipeout of the NMR signal. These signatures emerge below approximately
100-150 K, depending on the doping level, and reach a maximum onset
temperature around the nematic quantum critical point. Here we
present NMR data under uniaxial strain in Ba(CoxFe1-x)2As2 (x=0.08) at
the nematic quantum critical point. The relaxation behavior reveals
inhomogeneous relaxation that is strongly temperature-dependent and
hysteretic with strain. The stretching exponent, which probes the
degree of inhomogeneity, remains unchanged under strain. These results
suggest that the inhomogeneous relaxation observed by NMR reflects a
nematic glass, in which large random strain fields are present and
frustrate long-range nematic order.