The origin of the anomalous superconducting properties of MgB2

Hyoung Joon Choi, David Roundy, Hong Sun, Marvin L. Cohen and Steven G. Louie ()
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Hyoung Joon Choi: University of California at Berkeley
David Roundy: University of California at Berkeley
Hong Sun: University of California at Berkeley
Marvin L. Cohen: University of California at Berkeley
Steven G. Louie: University of California at Berkeley

Nature, 2002, vol. 418, issue 6899, 758-760

Abstract: Abstract Magnesium diboride1 differs from ordinary metallic superconductors in several important ways, including the failure of conventional models2 to predict accurately its unusually high transition temperature, the effects of isotope substitution on the critical transition temperature, and its anomalous specific heat3,4,5. A detailed examination of the energy associated with the formation of charge-carrying pairs, referred to as the ‘superconducting energy gap’, should clarify why MgB2 is different. Some early experimental studies have indicated that MgB2 has multiple gaps3,4,5,6,7,8,9, but past theoretical studies10,11,12,13,14,15,16 have not explained from first principles the origin of these gaps and their effects. Here we report an ab initio calculation of the superconducting gaps in MgB2 and their effects on measurable quantities. An important feature is that the electronic states dominated by orbitals in the boron plane couple strongly to specific phonon modes, making pair formation favourable. This explains the high transition temperature, the anomalous structure in the specific heat, and the existence of multiple gaps in this material. Our analysis suggests comparable or higher transition temperatures may result in layered materials based on B, C and N with partially filled planar orbitals.

Date: 2002
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DOI: 10.1038/nature00898

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