Uniaxial Strain Dependence of $T_c$ in ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{O}_7$: Internal Strain Induced Intralayer Charge Transfer

Results of ab initio calculations on uniaxially strained ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ are correlated with known values of the uniaxial strain dependencies ${\mathrm{dT}}_c/d{\epsilon }_{\alpha }$ $(\alpha =x,y,z)$ of the superconducting critical temperature $T_c$. Internal strains are found to dominate the strain dependence, with the strong nontetragonality correlating directly with the measured nontetragonality of ${\mathrm{dT}}_c/d{\epsilon }_{\alpha }$. Charge rearrangements within the ${\mathrm{CuO}}_2$ layers overwhelm any chain-to-layer charge transfer and strongly suggest that the relative amount of Cu and O character within the layers determines the strain dependence of $T_c$.