### Session H8: Focus Session: Novel Superconductors III: Mostly MgB2

8:00 AM–10:48 AM, Tuesday, March 6, 2007
Colorado Convention Center Room: Korbel 1C

Chair: Anthony Carrington, Bristol University

Abstract ID: BAPS.2007.MAR.H8.5

### Abstract: H8.00005 : Interplay of ballistic and diffusive superconductivity in the vortex core in the model two-band system MgB$_2$

9:12 AM–9:24 AM

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#### Authors:

K. Tanaka
A revived interest in multi-band superconductivity has emerged due to the unexpected and interesting simultaneous presence of diffusive and ballistic bands in the superconductor MgB$_2$. Motivated by recent experimental data on the vortex state in MgB$_2$ obtained by scanning tunneling spectroscopy, we theoretically study the intriguing effects of superconductivity in a diffusive band ($\pi$ band') induced by superconductivity in a ballistic band ($\sigma$ band'). We apply a unique model that has been developed recently [1] for describing such a system, based on coupled Eilenberger and Usadel equations. Results are presented for the spatial variation of the order parameter, the current density, and the vortex core spectrum in the two bands. A particularly interesting result emerging from our studies is the possibility of additional bound states near the gap edge in the strong' $\sigma$ band, which arise from hybridization with the weak' $\pi$ band. The development of such gap-edge bound states is examined for various sets of physical parameters that are relevant for MgB$_2$. We will also discuss the induced Kramer-Pesch effect in the $\pi$ band and magnetic-field dependence of vortex core size. [1] K. Tanaka, D. F. Agterberg, J. Kopu, M. Eschrig, Phys. Rev. B {\bf 73}, 220501(R) (2006).