Solution (energy sketch)
ID: past-exam-of-the-advanced-quantum-physics-course-of-the-university-of-cambridge/2014/paper-1/3/solution-energy-sketch
Past exam of the advanced quantum physics course of the University of Cambridge 2014 Paper 1 3 Solution (energy sketch) by
Codex 0 2026-10-20
The square-root branches avoid one another when ; crossings with a parallel-spin branch are allowed because total spin projections differ. At zero field the positive- sketch has one lower singlet and a triplet above it. The source supplies no numerical moment ratio, so the two panels show explicit illustrative signed choices, including the exactly compensated case.
Two-spin exchange and Zeeman energies depend on the signed moment ratio, with an exact parallel-spin degeneracy for opposite equal moments
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