We know some supercondutors show multi-gaps feature in superconducting energy gap (for example, two gaps in the MgB2), but other are singe-gap. Why they are different? Under what circumstances will single-gap and multiple-gaps be formed? Are there some references about it? And how can I distinguish them from some theories or properties? I'm very eager to know this question！
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Superconductors with two gaps will usually exhibit two separate superconducting phase transitions. In MgB2, there are two peaks in the specific heat at different temperatures. The transitions occur in two different bands.
Probably the most important difference to superconductors that exhibit only one transition is that superconductors with two gaps can exhibit a kind of internal Josephson effect and a so-called Leggett collective mode as a result. This has been claimed to have been observed in MgB2 with Raman spectroscopy.
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$\begingroup$ Thank you! Can you give me some ideas about Why the multi-gaps can be formed? Or what materials would be multi-gap? What would be sigle-gap? Are there some theories to Prejudge it before experiments and calculations? $\endgroup$– ming xiaCommented Jan 29 at 7:06
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$\begingroup$ Not that I know of... These kinds of properties of superconductors are very difficult to predict. Usually two-gap superconductors are experimentally discovered. $\endgroup$– XcheckrCommented Jan 29 at 11:13