Level Repulsion and Inhomogeneous Broadening: Ambrose and Sievers Find a Cusp (52)

Pat Ambrose and Al Sievers came by one day early in December with the weirdest line shape: instead of the Gaussian shape normally seen for absorption lines in solids theirs had a funny cusp right in the middle. The Central Limit Theorem tells us that the sum of lots of random strain fields should look Gaussian. Because their defect had a degenerate state in the absence of strain, it exhibited level repulsion: two different components of strain had to vanish simultaneously to get absorption in the middle. Someday I'd like to connect this to the universal level statistics seen in random matrix theory.

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Last modified: December 12, 1994

James P. Sethna,

Statistical Mechanics: Entropy, Order Parameters, and Complexity, now available at Oxford University Press (USA, Europe).