The electric field gradient (EFG) tensor at the As75 site couples to the orbital occupations of the As p orbitals and is a sensitive probe of local nematicity in BaFe2As2. We use nuclear magnetic resonance to measure the nuclear quadrupolar splittings and find that the EFG asymmetry responds linearly to the presence of a strain field in the paramagnetic phase. We extract the nematic susceptibility from the slope of this linear response as a function of temperature and find that it diverges near the structural transition, in agreement with other measures of the bulk nematic susceptibility. Our work establishes an alternative method to extract the nematic susceptibility which, in contrast to transport methods, can be extended inside the superconducting state.
Bibliographical noteFunding Information:
We thank S. Hillbrand, K. Delong, D. Hemer, and P. Klavins for assistance in the laboratory, and E. Carlson and I. R. Fisher for stimulating discussions. Work at UC Davis was supported by the NSF under Grant No. DMR-1506961 (T.K., M.L., B.T.B., and N.J.C.), NSF Grant No. DMR-1607139 (W.F.G.), and DOE NNSA Grant No. DE-NA0002908 (W.E.P.). R.M.F. is supported by the US Department of Energy, Office of Science, Basic Energy Sciences, under Award No. DE-SC0012336. R.S. was partially supported by the DFG through SFB 1143 for the project C02. Work done at Ames Lab (S.L.B., P.C.C., M.T., R.P., and E.I.T.) was supported by the US Department of Energy, Office of Basic Energy Science, Division of Materials Sciences and Engineering. Ames Laboratory is operated for the US Department of Energy by Iowa State University under Contract No. DE-AC02-07CH11358.