The g factor of electrons and holes in crystals and het erostructures of silicon\, germanium\, galium arsenide\, etc.\, is a k ey parameter in designing spin qubits. I will begin by discussing two different but interrelated definitions of the g factor. Authors have d isagreed from the beginning about whether or not g is a symmetric seco nd-rank tensor. I will discuss that g\, which is specific to each eige nstate\, whether extended or localized\, is best discussed in terms of three singular values associated with eigendirections\, with a separa te discussion about its sign. Luttinger gave a correct formula for the g factors of band electrons\, including the orbital contributions ari sing from the spin-orbit interaction. But it was not until fifty years later\, with the advent of Berry-curvature concepts\, that his formul a could be given a clear physical interpretation. I will show results of a survey we have done of band g factors in silicon and germanium\, emphasizing new topological aspects. It is interesting that even silic on\, with its very weak spin-orbit interaction\, can\, because of a co mbination of topology and symmetry\, exhibit g factors very far from 2 .

\nThis event starts at 3:30pm with refreshments\, followed at 3:45pm by a short presentation by Merritt Losert (PhD student Mark Fr iesen group)\, titled "Valley Splitting and Spin Shuttling in Si/SiGe Heterostructures". The invited presentation starts at 4pm. \n

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