Electronic structure of disordered solids – David A. Drabold

Date: Mon. April 16th, 2012, 12:30 pm-1:30 pm
Location: Rockefeller 221

Understanding the physics of structurally disordered materials is a challenge to experimentalists and theorists alike. In this talk, I discuss the character of electronic states in disordered materials and emphasize the interplay between structure and electronic properties. I begin by discussing the consequences of atomic structural disorder on electron states. As shown long ago by Anderson, disorder in atomic coordinates creates spatially confined or “localized” electron eigenstates near the Fermi level. I explore these states with large and realistic structural models and suitable electronic structure techniques. I begin with the structure of electron states in large and realistic models of a-Si, glassy silica and amorphous graphene, and find that important aspects of the states are universal (similar in different materials, and even for different physical quantities, such as classical vibrations). Next, we demonstrate the existence of subtle spatial correlations in the atomic coordinates of realistic models of a-Si (filaments or strings of connected long or short bonds) and show that these structures are responsible for the electronic band tails measured in photoemission and optical absorption experiments (also the states of greatest technological interest). The impact of the electronic structure on the atomic structure is discussed next, and I show that the electron states near the Fermi level determine the range of interatomic interactions, and thus play an important role in determining the structure itself.