Nuclear Acoustic Resonance Measurements of the Electron-Phonon Interaction in bcc Transition Metals
From pair-potential-model based analyses it has been deduced /1/ that in metals a substantial fraction of the outer electrons of atoms are highly incompressible but shape deformable. It is therefore expected that phononinduced changes in the shape of the electron spatial charge distribution will play the dominant role in the volume conserving part of the electron-phonon interaction. Confining ourselves to cubic metals, it is easy to realize that changes in the shape of the electron cloud may only be accomplished by the shear part \( \widehat \in \) (i.e. the volume conserving part) of the strain field e, whereas changes in volume will originate from the isotropic so-called hydrostatic part 1 · Tr є. If, on the other hand, the Wigner-Seitz cells of a cubic metal are (homogenously) strained by a long-wavelength (λ ≫ λDebye) ultrasonic shear mode, then the lowest electric multi-pole field of each Wigner-Seitz cell is no longer the 16-pole field — as in the undistorted (or “hydrostatically”strained) cubic crystal — but the strain-induced dynamic electric field gradient (DEFG) tensor \( \widehat V \) whose components can be determined in a nuclear acoustic resonance (NAR) experiment. NAP measurements of the DEFG in transition metals should therefore provide detailed informations about the electron-phonon interaction — in particular that of d electrons — which otherwise are hard to obtain.
KeywordsShape Deformable Shear Part Transition Metal Series Hydrostatic Part Nuclear Acoustic Resonance
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