Scientific Computing Seminar

Date:
Monday, March 7, 2005
Time:
10:30am-11:30am
Location:
50B-4205
Seminar Speaker:
Joshua Schrier
Dept. of Chemistry, UC Berkeley
jschrier (AT) berkeley (DOT) edu
Title:
Spins in Tight Places: Theoretical studies of spin properties in nanocrystals and fullerenes
Abstract:
Colloidal semiconductor nanocrystals have attracted attention not only because of their size tunable optical properties, but also because of the long-lived spin coherences resulting from three-dimensional confinement. Time-resolved Faraday rotation experiments have enabled measurement of the spin properties in isolated nanocrystals, and more recently, coherent spin transfer between molecularly linked nanocrystals. I will discuss work on the development of atomistic semi-empirical tight-binding methods for calculating the Lande g-factor of electrons, holes, and excitons in nanometer sized colloidal II-VI nanocrystals. The methods will be developed from perturbative theory through finite field treatments, and will describe the role of nanocrystal aspect ratio on the g-factor. I will then discuss work on an atomistic method for calculatng the spin transfer between the linked nanocrystals. Besides reproducing the experimental results, we study the role of surface site attachment (obscured in ensemble experimental studies), and predict an "on-off" behavior due to quantum interference in the linking molecule, which may server as a possible test of the coherent transfer hypothesis.

I will conclude with some recent work on the spin properties of atoms confined within fullerenes. First, I will discuss density-functional studies of Gd@C82 which describe a Gd position unlike the other lanthanide metallofullerenes, which explains previous discrepancies between theory and experimentally measured magnetic properties and oxidation states. Second, I will describe a simple model theory for the effect of endohedral confinement on the hyperfine coupling constant of nitrogen, which enables a rationalization of experimental measurements, and allows study of the comparative influences of fullerene size and pi-electron number on the hyperfine coupling constant.

Sponsor of Seminar:
Lin-Wang Wang
Scientific Computing

Contact Esmond G. Ng EGNg@lbl.gov