Pressure dependence of the electric-field gradients in YBa2Cu4O8

C.O. RODRIGUEZ; G. FABRICIUS; M.G. STACHIOTTI; N.E. CHRISTENSEN

PHYSICA C - SUPERCONDUTIVITY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1997 vol. 282 p. 1619 - 1620

0921-4534

The behaviour of the electric field gradients (EFGs) at all nuclear sites for YBa2Cu4O8 (Y124) under pressure have been obtained within the Local Density Approximation (LDA) to density functional (DFT), using the FP-LAPW method. The need for using an extended basis to deal with errors due to extended core states or linearization of narrow states is demonstrated by comparing our results to those obtained using the more standard two panel scheme. The calculated EFGs at ambient pressure for plane and chain Cu and O sites agree with already published theoretical values, but those of Y and Ba are quite different. The EFG's for which there exist experimental determinations are reproduced except for plane-Cu, where a factor 3 discrepancy is found. This is similar to the case of Y123, where the EFG's of the plane-Cu were off by a factor of 2. The smaller predicted anisotropy has been attributed to a real failure of LDA. As pressure is increased the calculated EFGs at plane-sites remain practically constant. Since many properties of Y124, including Tc, are very sensitive to pressure we propose that experimental evaluation of the EFGs under pressure could be used to give insight to charge redistributions in the CuO2 planes and to examine further the validity of predictions based of LDA calculations for High Tc materials(HTSC)