Band Structure of Noble Metal Alloys: Optical Absorption in Cu-Ge Alloys at 4.2°K

Abstract

Calorimetric optical absorption measurements at 4.2\ifmmode^\circ\else\textdegree\fi{}K have been made on a representative series of copper-germanium alloys, over the wavelength range 0.23 to 4 microns, using electropolished bulk specimens. The variation of the infrared absorptivity with residual resistance for the dilute alloys confirms that the impurity relaxation time for copper is anisotropic. Changes in the absorption spectrum below 6000 A are inconsistent with the rigid band model, but may be reconciled with the theory of Cohen and Heine. The shift in the main absorption edge is analyzed to give information about the screening of the solute atoms in these alloys.