Phase stability in SmB 6

We investigate flux-grown Sm-deficient ${\mathrm{Sm}}_{x}{\mathrm{B}}_{6}$ ($xl1$) by global and local tools, including x-ray diffraction (XRD), electronic transport, and scanning tunneling microscopy (STM) and spectroscopy (STS). All these tools indicate a remarkable persistence of the ${\mathrm{SmB}}_{6}$ local structure in the flux-grown samples even for nominal Sm concentrations as low as $x=0.75$. As a consequence, the overall electronic properties of ${\mathrm{Sm}}_{x}{\mathrm{B}}_{6}$, and particularly the surface conductance at low temperature, are only affected locally by the Sm deficiency.