Tunneling Modes and Local Structural Order in Amorphous Arsenic

Abstract

Pulsed nuclear-quadrupole-resonance (NQR) measurements have been performed in rhombohedral, orthorhombic, and amorphous ($a\ensuremath{-}$) arsenic. Measurements of ${T}_{1}$ provide evidence of low-frequency disorder modes in $a$-As, while the NQR frequencies indicate that the bonding is predominately $p$-like in all three materials. The asymmetric NQR line shape of $a$-As indicates that bond-angle distributions inferred from x-ray scattering and continuous-random-network models do not result primarily from a distribution in bond hydridizations.