Contribution of Electromagnetic Field to Atomic Spin |
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Authors: | DU Tao LIANG Wen-Feng WU Xiao-Hua |
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Institution: | Department of Physics, Sichuan University, Chengdu 610064, China |
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Abstract: | We examine the contribution of electromagnetic field to the atomic spin, by adopting two different, both gauge invariant definitions of the electromagnetic angular momentum: \vec{J}I ≡ ∫d3 x ε0 \vec{r} X (\vec{E} X \vec{B}) and \vec{J}II ≡ ∫d3 x ( ε0 \vec{E} X \vec{A}^\bot + ε0 Ei \vec{r} X \vec{\nabla }A^{\bot}i ). Notably, at the classical level, \vec{J}II gives an exactly null result while \vec{J}I gives a finite value. This suggests that \vec{J}II leads to a simpler and more reasonable picture of the atomic spin, therefore qualifies as a more appropriate definition of the electromagnetic angular momentum. Our observation gives important hint on the delicate issue of gluon contribution to the nucleon spin. |
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Keywords: | spin structure electromagnetic angular momentum |
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