Abstract
MgB2 with Tc ≈ 40 K, is a record-breaking compound among the s-p metals and alloys. It appears that this material is a rare example of the two band electronic structures, which are weakly connected with each other. Experimental results clearly reveal that boron sub-lattice conduction band is mainly responsible for superconductivity in this simple compound. Experiments such as tunneling spectroscopy, specific heat measurements, and high resolution spectroscopy show that there are two superconducting gaps. Considering a canonical two band BCS Hamiltonian containing a Fermi Surface of π- and σ-bands and following Green’s function technique and equation of motion method, we have shown that MgB2 possess two superconducting gaps. It is also pointed out that the system admits a precursor phase of Cooper pair droplets that undergoes a phase locking transition at a critical temperature below the mean field solution. Study of specific heat and density of states is also presented. The agreement between theory and experimental results for specific heat is quite convincing. The paper is organized in five sections: Introduction, Model Hamiltonian, Physical properties, Numerical calculations, Discussion and conclusions.
Highlights
The surprising discovery of superconductivity in the novel system MgB2 with Tc = 39 K by Nagamatsu et al [1] has stimulated new excitement in condensed matter physics
Considering a canonical two band BCS Hamiltonian containing a Fermi Surface of π- and σ-bands and following Green’s function technique and equation of motion method, we have shown that MgB2 possess two superconducting gaps
We study the basic MgB2 superconductivity characteristics, specific heat and density of states and compare the theoretical results qualitatively with the available experimental data
Summary
The magnesium atoms are arranged between the boron layers in the centers of the hexagons This has allowed to perform consistent calculations of its electronic structure. Band structure calculations of MgB2 show that there are at least two types of nearly separated bands with two superconducting gaps in the excitation spectrum at the Fermi surface. Ummarino et al [12] proposed that MgB2 is a weak coupling two band phononic system where the Coulomb pseudopotential and the interchannel paring mechanism are key terms to interpret the superconducting state. It is quite natural to describe a two-gap superconductor by means of a two-band model with interband coupling [14,15]. Liu et al [4] pointed the role of the electron-phonon interaction between effective σ- and π-bands in the two gap system MgB2. We study the basic MgB2 superconductivity characteristics, specific heat and density of states and compare the theoretical results qualitatively with the available experimental data
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