Near-surface properties of SrTiO$_{3}$ (001) from resonant soft x-ray reflectance*

Resonant reflectivity $R$(\textit{h$\nu $}, $q)$ has been measured from several SrTiO$_{3}$ (001) single crystals across the Ti $L_{2,3}$ edges: we find that this approach senses the near-surface region differently than other techniques including resonant XAS via total electron yield. Modeling $R$(\textit{h$\nu $}) provides absolute resonant optical properties $n$ = 1 -- \textit{$\delta $} -- \textit{i$\beta $} indicating short skin depths ($<$ 10 nm) when tuned to the $t_{2g}$ and $e_{g}$ peaks. We observe unexpected linear dichroism (LD) at 300 K primarily in the $e_{g}$ states, consistent with tetragonal symmetry and possible weak ferroelectric polarization. Below the bulk antiferrodistortive transition at 105 K both $t_{2g}$ and $e_{g}$ states exhibit LD. Resonant $R(q)$ exhibits clear structure indicating a subsurface layer several nm thick having different properties from the bulk, suggesting that the 300 K LD is associated with this layer. We discuss these new results in the context of established studies of the STO surface and their relevance to dielectric and ferroelectric properties of STO surfaces and thin films.