Spin Spiral vs. Spin Stripe in La_2−xBa_xCuO₄ (x = $\frac{1}{8}$): Analysis of μSR Data

There are two models that explain the incommensurate elastic neutron scattering from ${\mathrm{La}}_{2-x}{\mathrm{Ba}}_x{\mathrm{CuO}}_4$ ($x={\displaystyle \frac{1}{8}}$), (i) spin spiral and (ii) collinear spin stripe. I show that available $\mu$SR data taken with a polycrystalline sample is consistent with the generic (arbitrary parameters) coplanar spin spiral. On the other hand for consistency with the collinear spin stripe one needs fine tuning of the parameters of the model. I also propose a further $\mu$SR experiment with a single crystal aimed specifically at the window of parameters where the spin stripe model is still consistent with the data. In the proposed experiment, the expected signals for these two models are dramatically different. Such an experiment would finally reject one of the models.