Tunneling in Two-Band Superconductor MgB₂

Figure - Scanning electron micrograph, STM topography, and tunneling spectroscopy on c-axis ordered thin film (top) and disordered thin film (bottom) of MgB₂ at 4.2 K in ambient magnetic field. When tunneling along the a-b plane (bottom) the 2D superconducting gap is pronounced in the tunneling spectra.

The discovery of superconductivity in MgB₂ at 39K sparked great interest in the fundamental physics and practical applications of this material. The existence of two gaps in this material is one of the most peculiar features in this binary superconductor. We study the anisotropic superconductor using a combination of scanning tunneling microscopy and spectroscopy and we find the existence of two distinct superconducting energy gaps at 2.3 meV and 7.1 meV.

Different spectral weights of the partial superconducting density of states are a reflection of different tunneling directions in this multi-band system. Our experimental observations are consistent with the existence of two-band superconductivity in the presence of interband superconducting pair interaction and quasiparticle scattering. We have conducted extended studies on this system in single crystalline and thin film form with and without presence of disorder.

Recent Publications:

• Characterization of off-axis MgB₂ Epitaxial Thin Films for Planar Junctions, M. Iavarone, G. Karapetrov, A. Menzel, V. Komanicky, H. You, W.K. Kwok,P. Orgiani, V. Ferrando, X.X. Xi, Appl. Phys. Lett. 87 , p. 242506 (2005)
• Effect of Disorder in MgB₂ Thin Films, M. Iavarone, A. Koshelev, W.K. Kwok, R. DiCapua, R. Vaglio, A. Pogrebnyakov, X.X. Xi, S.I. Lee, Phys. Rev. B 71 , p.214502 (2005)
• Phase Diagram of Single Crystal MgB2G. Karapetrov, U. Welp, A. Rydh, M. Iavarone, W. K. Kwok, G. W. Crabtree, Ch. Marcenat, L. Paulius, T. Klein, J. Marcus, K. H. P. Kim, C. U. Jung, H.-S. Lee, B. Kang, S.-I. Lee, J. Low Temp. Phys. 131 p.1237-1244 (2003)
• Two-band Superconductivity in MgB2, M. Iavarone, G. Karapetrov, W.K.Kwok, G.W. Crabtree, D.G. Hinks, W. N. Kang, Eun-Mi Choi, Hyun Jung Kim, Hyeong-Jin Kim and S. I. Lee, Phys. Rev. Lett. 89, p.187002 (2002)