L-edge x-ray absorption in fcc and bcc Cu metal: Comparison of experimental and first-principles theoretical results

High resolution Cu ${\mathit{L}}_{2,3}$ x-ray absorption spectra of bulk fcc Cu metal are compared with those of thin Cu layers in Cu/Fe multilayers. Comparison of the measured fine structure with that obtained from a fully relativistic first-principles calculation for fcc and bcc Cu reveals that Cu is bcc in Cu(3 Å)/Fe(10 Å) and fcc in Cu(10 Å)/Fe(3 Å) multilayers. This result indicates that the thicker layer simply acts as a template for the structure of the thinner layer. The excellent agreement between experimental and theoretical spectra also demonstrates the validity of the theoretical approach. The theoretical spectra are discussed in terms of their angular momentum composition and the energy dependence of the radial transition matrix elements. © 1996 The American Physical Society.