Europhys. Lett.
Volume 61, Number 2, January 2003
Page(s) 254 - 260
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 01 January 2003
DOI: 10.1209/epl/i2003-00102-1
Europhys. Lett., 61 (2) , pp. 254-260 (2003)

${\mu^+}$SR study of carbon-doped $\chem{MgB_2}$ superconductors

K. Papagelis1, J. Arvanitidis1, K. Prassides1, A. Schenck2, T. Takenobu3 and Y. Iwasa3

1  School of Chemistry, Physics and Environmental Science, University of Sussex Brighton BN1 9QJ, UK
2  Institute for Particle Physics, ETH Zurich - CH-5232 Villigen PSI, Switzerland
3  Institute for Materials Research, Tohoku University - Sendai 980-8577, Japan and CREST, Japan Science and Technology Corporation - Kawaguchi 332-0012, Japan

(Received 24 July 2002; accepted 7 November 2002)

The evolution of the superconducting properties of the carbon-doped $\chem{MgB_2}$ superconductors, $\chem{MgB}$ 2-x $\chem{C}$ x ( x= 0.02, 0.04, 0.06) have been investigated by the transverse-field muon spin rotation (TF- ${\mu^+}$SR) technique. The low-temperature depolarisation rate, $\sigma(0)$ at 0.6 $\un{T}$ which is proportional to the second moment of the field distribution of the vortex lattice decreases monotonically with increasing electron doping and decreasing $T_\ab{c}$. In addition, the temperature dependence of $\sigma(T)$ has been analysed in terms of a two-gap model. The size of the two superconducting gaps decreases linearly as the carbon content increases.

76.75.+i - Muon spin rotation and relaxation.
74.70.Ad - Metals, alloys and binary compounds (including A15, Laves phases, etc.).
74.20.-z - Theories and models of superconducting state.

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