Effect of uniaxial strains on the electronic structure of YBa2Cu3O7

Local density approximation calculations of changes in the electronic structure of YBa2Cu3O7 under unaxial strain in each of the three orthorhombic directions are reported. Results are correlated viith known values of the uniaxial strain dependencies dT(c)/de(alpha) (alpha = x, y, z) of the superconducting critical temperature T-c. which are large and of opposite sign for strains within the (a) over cap-(b) over cap plane containing the CuO2 layers (i.e. strong non-tetragonality), and an order of magnitude smaller for (c) over cap-axis strain. The uniaxal strain dependencies of internal strains, zone center A(g) phonon frequencies, band structure, density of states, and charge transfer are obtained for finite (2%) strains. Internal strains show strong non-tetragonaiity, and the frequency of the highest A(g) mode is highly sensitive to (b) over cap-axis strain. Charge transfer between the chains and the layers is found to be negligible in comparison to the charge rearrangements within the layers themselves, which have a strong dipolar character and are directed oppositely for (a) over cap and (b) over cap-axis strains. This charge redistribution, which alters the Madelung potentials within the CuO2 layer and the ratio of Cu2 and O2, O3 character of states at the Fermi surface, is the most notable feature that correlates positively with the values of dT(c)/d(a), and dT(c)/d epsilon(b). (C) 1997 Elsevier Science B.V.