Uniaxial pressure dependence of ${\mathit{T}}_{\mathit{c}}$ from high-resolution dilatometry of untwinned ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_4$ single crystals

We have carried out high-resolution dilatometry experiments on a series of high-quality single crystals of ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$ with various Sr content on both the under- and overdoped side of the ${\mathit{T}}_{\mathit{c}}$(x) phase diagram. A simple in situ technique was applied to prevent the usual twinning of the samples in the low-temperature orthorhombic (LTO) phase, which allows us to study the full anisotropy of the thermal expansion of the LTO phase. From the anomalies in the linear expansivities Δ${\mathrm{\alpha }}_{\mathit{i}}$ (i=a,b,c) at ${\mathit{T}}_{\mathit{c}}$ we deduce all three uniaxial stress (${\mathit{dT}}_{\mathit{c}}$/${\mathit{dp}}_{\mathit{i}}$) and strain (${\mathit{dT}}_{\mathit{c}}$/d${\mathrm{\varepsilon }}_{\mathit{i}}$) dependences, which turn out to be large and almost cancel for hydrostatic pressure.