Wednesday, January 5, 2011
Varma's Current
The short review [http://arxiv.org/PS_cache/arxiv/pdf/1012/1012.5461v1.pdf] of the history of High Tc superconductivity by J.Zannen has mentioned the work by C. M.Varma, who proposed the so-called circulating current phase as a candidate explanation of the observed pseudogap phase [http://prl.aps.org/pdf/PRL/v83/i17/p3538_1]. As beautiful as it seems, one should take caution with this: such current is incompatible with the formation of Zhang-Rice singlets. The only claimed experimental support of this phase comes from Neutron scattering and optical experiments which detected a time-reversal symmetry breaking state. However, it might be too hasty to identify this phase with the Varma's phase. Let's wait and see how the holy grail will be won !
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As far as I'm concerned, the experiments by Bourges and Kapitulnik, using polarized neutrons and light respectively, only point at a time reversal symmetry breaking phase, which cannot be a priori nailed down as the Varma's current phase. Actually, the so-called checkerboard phase, which was found by Kohsaka et al. in the pseudogap regime, also claims time reversal symmetry breaking.
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