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.
Your institute does not have access to this article
Open Access articles citing this article.
npj Quantum Materials Open Access 01 April 2022
Scientific Reports Open Access 27 December 2019
npj Computational Materials Open Access 03 May 2019
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
Nagamatsu, J., Nakagawa, N., Muranaka, T., Zenitani, Y. & Akimitsu, J. Superconductivity at 39 K in magnesium diboride. Nature 410, 63–64 (2001)
Hinks, D. G., Claus, H. & Jorgensen, J. D. The complex nature of superconductivity in MgB2 as revealed by the reduced total isotope effect. Nature 411, 457–460 (2001)
Wang, Y., Plackowski, T. & Junod, A. Specific heat in the superconducting and normal state (2-300 K, 0-16 T), and magnetic susceptibility of the 38 K superconductor MgB2 . Physica C 355, 179–193 (2001)
Bouquet, F., Fisher, R. A., Phillips, N. E., Hinks, D. G. & Jorgensen, J. D. Specific heat of Mg11B2: evidence for a second energy gap. Phys. Rev. Lett. 87, 047001-1–047001-4 (2001)
Yang, H. D. et al. Order parameter of MgB2: a fully gapped superconductor. Phys. Rev. Lett. 87, 167003-1–167003-4 (2001)
Szabo, P. et al. Evidence for two superconducting energy gaps in MgB2 by point-contact spectroscopy. Phys. Rev. Lett. 87, 137005-1–137005-4 (2001)
Giubileo, F. et al. Two-gap state density in MgB2: a true bulk property or a proximity effect? Phys. Rev. Lett. 87, 177008-1–177008-4 (2001)
Chen, X. K., Konstantinovi, M. J., Irwin, J. C., Lawrie, D. D. & Franck, J. P. Evidence for two superconducting gaps in MgB2 . Phys. Rev. Lett. 87, 157002-1–157002-4 (2001)
Tsuda, S. et al. Evidence for a multiple superconducting gap in MgB2 from high-resolution photoemission spectroscopy. Phys. Rev. Lett. 87, 177006-1–177006-4 (2001)
Kortus, J., Mazin, I. I., Belashchenko, K. D., Antropov, V. P. & Boyer, L. L. Superconductivity of metallic boron in MgB2 . Phys. Rev. Lett. 86, 4656–4659 (2001)
An, J. M. & Pickett, W. E. Superconductivity of MgB2: covalent bonds driven metallic. Phys. Rev. Lett. 86, 4366–4369 (2001)
Bohnen, K.-P., Heid, R. & Renker, B. Phonon dispersion and electron-phonon coupling in MgB2 and AlB2 . Phys. Rev. Lett. 86, 5771–5774 (2001)
Yildirim, T. et al. Giant anharmonicity and nonlinear electron-phonon coupling in MgB2: a combined first-principles calculation and neutron scattering study. Phys. Rev. Lett. 87, 037001-1–037001-4 (2001)
Liu, A. Y., Mazin, I. I. & Kortus, J. Beyond Eliashberg superconductivity in MgB2: anharmonicity, two-phonon scattering, and multiple gaps. Phys. Rev. Lett. 87, 087005-1–087005-4 (2001)
Kong, Y., Dolgov, O. V., Jepsen, O. & Andersen, O. K. Electron-phonon interaction in the normal and superconducting states of MgB2 . Phys. Rev. B 64, 020501-1–020501-4 (2001)
Choi, H. J., Roundy, D., Sun, H., Cohen, M. L. & Louie, S. G. First-principles calculation of the superconducting transition in MgB2 within the anisotropic Eliashberg formalism. Phys. Rev. B 66, 020513-1–020513-4 (2002)
Eliashberg, G. M. Interactions between electrons and lattice vibrations in a superconductor. Zh. Eksp. Teor. Fiz. 38, 966–976 (1960); Sov. Phys. JETP 11, 696–702 (1960).
Allen, P. B. & Mitrović, B. in Solid State Physics (eds Ehrenreich, H., Seitz, F. & Turnbull, D.) Vol. 37 1–92 (Academic, New York, 1982)
Carbotte, J. P. Properties of boson-exchange superconductors. Rev. Mod. Phys. 62, 1027–1157 (1990)
Marsiglio, F., Schossmann, M. & Carbotte, J. P. Iterative analytic continuation of the electron self-energy to the real axis. Phys. Rev. B 37, 4965–4969 (1988)
Karapetrov, G., Iavarone, M., Kwok, W. K., Crabtree, G. W. & Hinks, D. G. Scanning tunneling spectroscopy in MgB2 . Phys. Rev. Lett. 86, 4374–4377 (2001)
Sharoni, A., Felner, I. & Millo, O. Tunneling spectroscopy and magnetization measurements of the superconducting properties of MgB2 . Phys. Rev. B 63, 220508-1–220508-4 (2001)
Rubio-Bollinger, G., Suderow, H. & Vieira, S. Tunneling spectroscopy in small grains of superconducting MgB2 . Phys. Rev. Lett. 86, 5582–5584 (2001)
Schmidt, H., Zasadzinski, J. F., Gray, K. E. & Hinks, D. G. Energy gap from tunneling and metallic contacts onto MgB2: possible evidence for a weakened surface layer. Phys. Rev. B 63, 220504-1–220504-4 (2001)
Takahashi, T., Sato, T., Souma, S., Muranaka, T. & Akimitsu, J. High-resolution photoemission study of MgB2 . Phys. Rev. Lett. 86, 4915–4917 (2001)
Buzea, C. & Yamashita, T. Review of superconducting properties of MgB2 . Supercond. Sci. Technol. 14, R115–R146 (2001)
Suhl, H., Matthias, B. T. & Walker, L. R. Bardeen-Cooper-Schrieffer theory of superconductivity in the case of overlapping bands. Phys. Rev. Lett. 3, 552–554 (1959)
Bardeen, J. & Stephen, M. Free-energy difference between normal and superconducting states. Phys. Rev. A 136, 1485–1487 (1964)
This work was supported by the National Science Foundation and by the Director, Office of Science, Office of Basic Energy Sciences of the US Department of Energy. Computational resources have been provided by the National Science Foundation at the National Center for Supercomputing Applications and by the National Energy Research Scientific Computing Center. H. S. acknowledges financial support from the Berkeley Scholar Program funded by the Tang Family Foundation.
The authors declare that they have no competing financial interests.
About this article
Cite this article
Choi, H., Roundy, D., Sun, H. et al. The origin of the anomalous superconducting properties of MgB2. Nature 418, 758–760 (2002). https://doi.org/10.1038/nature00898
npj Quantum Materials (2022)
npj Computational Materials (2019)
Scientific Reports (2019)
Effects of Ageing on the Microwave Surface Resistance of MgB2 Superconductor Films Stored in Low Vacuum
Electronic Materials Letters (2019)
Scientific Reports (2018)