### 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.H8.6

### Abstract: H8.00006 : Breakdown of phase-locked states and limit of the upper critical field controlled by interband scattering in two-gap superconductors.

9:24 AM–9:36 AM

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#### Author:

Alexander Gurevich
(National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA)

The effect of weak interband scattering on the maximum upper critical field $H_{c2}$, which can be achieved in a two-band superconductor by increasing intraband impurity scattering is considered. Using the two-gap Usadel equations, we show how weak interband scattering provides the crossover from the orbitally limited to the paramagnetically limited $H_{c2}$, both in bulk samples and thin films. The results are applied to describe high $H_{c2}$ values in carbon-doped MgB$_2$ films. It is shown that interband scattering produces mixed gradient terms $\propto Re(\Pi^{*}\Psi_\sigma^{*}\Pi\Psi_\pi)$ in the free energy, where $\Pi = \nabla +2\pi A/\phi_0$, and $\Psi_\sigma=\Delta_\sigma\exp(i\theta_\sigma)$ and $\Psi_\pi = \Delta_\pi\exp(i\theta_\pi)$ are intraband order parameters. The mixed gradient coupling can provide parametric excitation of the plasmon Legget mode or large-amplitude interband phase textures by ac currents.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2007.MAR.H8.6