Phase stability in SmB${}_6$

We investigate flux-grown Sm-deficient Sm${}_x$B${}_6$ ($x<1$) 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 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 Sm${}_x$B${}_6$, and particularly the surface conductance at low temperature, is only affected locally by the Sm-deficiency.